feat(machine/stm32): add STM32H7 and NUCLEO-H753ZI support

GNUmakefile

@@ -807,6 +807,8 @@ endif
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=pico -gc=leaking    examples/blinky1
 	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=pico-w              examples/blinky1
+	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=nano-33-ble         examples/blinky1
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=nano-rp2040         examples/blinky1
@@ -845,8 +847,14 @@ endif
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=pico2               examples/blinky1
 	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=pico2-w             examples/blinky1
+	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=tiny2350            examples/blinky1
 	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=badger2350          examples/blinky1
+	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=blinky2350          examples/blinky1
+	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=pico-plus2          examples/blinky1
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=metro-rp2350        examples/blinky1
@@ -888,6 +896,8 @@ ifneq ($(STM32), 0)
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=nucleo-f722ze       examples/blinky1
 	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=nucleo-h753zi       examples/blinky1
+	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=nucleo-l031k6       examples/blinky1
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=nucleo-l432kc       examples/blinky1

src/examples/pwm/nucleo-h753zi.go

@@ -0,0 +1,11 @@
+//go:build stm32h7
+
+package main
+
+import "machine"
+
+var (
+	pwm  = &machine.TIM1
+	pinA = machine.PA8
+	pinB = machine.PA9
+)

src/examples/wwdg/main.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"machine"
+	"time"
+)
+
+func main() {
+	time.Sleep(2 * time.Second)
+
+	println("configuring window watchdog")
+	config := machine.WindowWatchdogConfig{
+		TimeoutMicros: 100000, // 100ms
+		WindowPercent: 50,     // 50ms to 100ms refresh window
+	}
+
+	machine.WindowWatchdog.Configure(config)
+	machine.WindowWatchdog.Start()
+
+	println("updating wwdg for 1 second")
+	for i := 0; i < 10; i++ {
+		time.Sleep(75 * time.Millisecond) // middle of the window
+		machine.WindowWatchdog.Update()
+		println("alive")
+	}
+
+	println("entering tight loop (will reset)")
+	for {
+		time.Sleep(10 * time.Millisecond)
+	}
+}

src/machine/board_nucleoh753zi.go

@@ -0,0 +1,105 @@
+//go:build nucleoh753zi
+
+package machine
+
+import (
+	"device/stm32"
+	"runtime/interrupt"
+)
+
+const xtalHz = 8_000_000
+const hseBypass = true
+
+const (
+	// Arduino Pins
+	A0 = PA3
+	A1 = PC0
+	A2 = PC3
+	A3 = PB1
+	A4 = PC2
+	A5 = PF10
+
+	D0  = PG9
+	D1  = PG14
+	D2  = PF15
+	D3  = PE13
+	D4  = PF14
+	D5  = PE11
+	D6  = PE9
+	D7  = PF13
+	D8  = PF12
+	D9  = PD15
+	D10 = PD14
+	D11 = PA7
+	D12 = PA6
+	D13 = PA5
+	D14 = PB9
+	D15 = PB8
+)
+
+const (
+	LED         = LED_BUILTIN
+	LED_BUILTIN = LED_GREEN
+	LED_GREEN   = PB0
+	LED_YELLOW  = PE1
+	LED_RED     = PB14
+)
+
+const (
+	BUTTON      = BUTTON_USER
+	BUTTON_USER = PC13
+)
+
+// UART pins
+const (
+	// PD8 and PD9 are connected to the ST-Link Virtual Com Port (VCP)
+	UART_TX_PIN = PD8
+	UART_RX_PIN = PD9
+	UART_ALT_FN = AF7_SPI2_3_USART1_2_3_UART5_SPDIFRX
+)
+
+var (
+	// USART3 is the hardware serial port connected to the onboard ST-LINK
+	// debugger to be exposed as virtual COM port over USB on Nucleo boards.
+	UART1  = &_UART1
+	_UART1 = UART{
+		Buffer:            NewRingBuffer(),
+		Bus:               stm32.USART3,
+		TxAltFuncSelector: UART_ALT_FN,
+		RxAltFuncSelector: UART_ALT_FN,
+	}
+	DefaultUART = UART1
+)
+
+func init() {
+	UART1.Interrupt = interrupt.New(stm32.IRQ_USART3, _UART1.handleInterrupt)
+}
+
+// SPI pins
+const (
+	SPI0_SCK_PIN = PA5
+	SPI0_SDI_PIN = PA6
+	SPI0_SDO_PIN = PA7
+)
+
+var (
+	SPI1 = &SPI{
+		Bus:             stm32.SPI1,
+		AltFuncSelector: AF5_SPI1_2_3_4_5_6_I2S,
+	}
+	SPI0 = SPI1
+)
+
+// I2C pins
+const (
+	I2C0_SCL_PIN = PB8
+	I2C0_SDA_PIN = PB9
+)
+
+var (
+	I2C1 = &I2C{
+		Bus:             stm32.I2C1,
+		AltFuncSelector: AF4_I2C1_2_3_4_USART1,
+	}
+	I2C0 = I2C1
+)

src/machine/machine_stm32.go

@@ -86,12 +86,6 @@ func (p Pin) PortMaskClear() (*uint32, uint32) {
 	return &port.BSRR.Reg, 1 << (pin + 16)
 }
 
-// EnterBootloader resets the chip into the bootloader.
-// This is currently a stub for STM32, required to satisfy machine.EnterBootloader
-// called by machine/usb/cdc.
-func EnterBootloader() {
-}
-
 var deviceID [12]byte
 
 // DeviceID returns an identifier that is unique within

src/machine/machine_stm32_adc_h7.go

@@ -0,0 +1,184 @@
+//go:build stm32h7
+
+package machine
+
+import (
+	"device/arm"
+	"device/stm32"
+)
+
+// InitADC initializes the registers needed for ADC1 and ADC3.
+func InitADC() {
+	// 1. Enable ADC bus clocks
+	stm32.RCC.AHB1ENR.SetBits(stm32.RCC_AHB1ENR_ADC12EN)
+	stm32.RCC.AHB4ENR.SetBits(stm32.RCC_AHB4ENR_ADC3EN)
+
+	// 2. Configure ADC clock mode (Async from kernel clock)
+	// CCR is at offset 0x308 from ADC base.
+	stm32.ADC12_Common.CR.ReplaceBits(0x0, 0x3, 16) // CKMODE = 00
+	stm32.ADC3_Common.CR.ReplaceBits(0x0, 0x3, 16)  // CKMODE = 00
+
+	// 3. Exit deep power-down mode
+	stm32.ADC1.CR.ClearBits(stm32.ADC_CR_DEEPPWD)
+	stm32.ADC3.CR.ClearBits(stm32.ADC_CR_DEEPPWD)
+
+	// 4. Enable voltage regulators
+	stm32.ADC1.CR.SetBits(stm32.ADC_CR_ADVREGEN)
+	stm32.ADC3.CR.SetBits(stm32.ADC_CR_ADVREGEN)
+	// Wait for T_ADCVREG_STUP (min 10us). The nop keeps the compiler from
+	// eliminating the loop as free of side effects.
+	for i := 0; i < 10000; i++ {
+		arm.Asm("nop")
+	}
+
+	// Set BOOST[1:0]=0b11 for ADC kernel clock >25MHz (RM0433 §25.4.3 Table 121).
+	// The kernel clock is 80MHz (PLL2_P), so BOOST must be enabled.
+	stm32.ADC1.CR.ReplaceBits(0b11, 0x3, stm32.ADC_CR_BOOST_Pos)
+	stm32.ADC3.CR.ReplaceBits(0b11, 0x3, stm32.ADC_CR_BOOST_Pos)
+
+	// 5. Calibration
+	// ADC1
+	stm32.ADC1.CR.SetBits(stm32.ADC_CR_ADCAL | stm32.ADC_CR_ADCALLIN)
+	for stm32.ADC1.CR.HasBits(stm32.ADC_CR_ADCAL) {
+	}
+	// ADC3
+	stm32.ADC3.CR.SetBits(stm32.ADC_CR_ADCAL | stm32.ADC_CR_ADCALLIN)
+	for stm32.ADC3.CR.HasBits(stm32.ADC_CR_ADCAL) {
+	}
+
+	// 6. Enable ADCs
+	// ADC1
+	stm32.ADC1.ISR.SetBits(stm32.ADC_ISR_ADRDY) // Clear ADRDY by writing 1
+	stm32.ADC1.CR.SetBits(stm32.ADC_CR_ADEN)
+	for !stm32.ADC1.ISR.HasBits(stm32.ADC_ISR_ADRDY) {
+	}
+	// ADC3
+	stm32.ADC3.ISR.SetBits(stm32.ADC_ISR_ADRDY) // Clear ADRDY by writing 1
+	stm32.ADC3.CR.SetBits(stm32.ADC_CR_ADEN)
+	for !stm32.ADC3.ISR.HasBits(stm32.ADC_ISR_ADRDY) {
+	}
+
+	// 7. Configure resolution (16-bit)
+	// RES[2:0] is at bits 4:2 in CFGR. 000: 16-bit.
+	stm32.ADC1.CFGR.ReplaceBits(0x0, 0x7, 2)
+	stm32.ADC3.CFGR.ReplaceBits(0x0, 0x7, 2)
+}
+
+// Configure configures an ADC pin to be able to read analog data.
+func (a ADC) Configure(config ADCConfig) {
+	a.Pin.Configure(PinConfig{Mode: PinInputAnalog})
+
+	// Set sampling time.
+	// H7 has SMPR1 (channels 0-9) and SMPR2 (channels 10-19).
+	// Each channel has 3 bits.
+	ch := a.getChannel()
+	adc, _ := a.getPeripheral()
+	const smpVal = 0x2 // 8.5 cycles
+	if ch <= 9 {
+		adc.SMPR1.ReplaceBits(uint32(smpVal), 0x7, uint8(ch)*3)
+	} else {
+		adc.SMPR2.ReplaceBits(uint32(smpVal), 0x7, uint8(ch-10)*3)
+	}
+}
+
+// Get returns the current value of an ADC pin in the range 0..0xffff.
+func (a ADC) Get() uint16 {
+	ch := uint32(a.getChannel())
+	adc, ok := a.getPeripheral()
+	if !ok {
+		return 0
+	}
+
+	// Select channel (PCSEL register)
+	// Refer to RM0433 §25.4.12: Only one PCSELx bit must be set at a time.
+	adc.PCSEL.Set(1 << ch)
+
+	// Set rank 1 to channel
+	// SQ1[4:0] at bits 10:6. L[3:0] at bits 3:0.
+	adc.SQR1.ReplaceBits(ch, 0x1F, 6)
+	adc.SQR1.ReplaceBits(0x0, 0xF, 0) // L=0 (1 conversion)
+
+	// Start conversion
+	adc.CR.SetBits(stm32.ADC_CR_ADSTART)
+
+	// Wait for end of conversion
+	for !adc.ISR.HasBits(stm32.ADC_ISR_EOC) {
+	}
+
+	// Read 16-bit result
+	result := uint16(adc.DR.Get())
+
+	// Clear EOC
+	adc.ISR.SetBits(stm32.ADC_ISR_EOC)
+
+	// Deselect channel
+	adc.PCSEL.Set(0)
+
+	return result
+}
+
+func (a ADC) getPeripheral() (*stm32.ADC_Type, bool) {
+	switch a.Pin {
+	case PF3, PF4, PF5, PF6, PF7, PF8, PF9, PF10:
+		return stm32.ADC3, true
+	default:
+		// Assume ADC1 for PA/PB/PC pins
+		return stm32.ADC1, true
+	}
+}
+
+// getChannel returns the ADC channel number for a given GPIO pin.
+// Mapping for STM32H743 per RM0433 and DS12110.
+func (a ADC) getChannel() uint8 {
+	switch a.Pin {
+	case PA0:
+		return 16
+	case PA1:
+		return 17
+	case PA2:
+		return 14
+	case PA3:
+		return 15
+	case PA4:
+		return 18
+	case PA5:
+		return 19
+	case PA6:
+		return 3
+	case PA7:
+		return 7
+	case PB0:
+		return 9
+	case PB1:
+		return 5
+	case PC0:
+		return 10
+	case PC1:
+		return 11
+	case PC2:
+		return 12
+	case PC3:
+		return 13
+	case PC4:
+		return 4
+	case PC5:
+		return 8
+	case PF3:
+		return 5
+	case PF4:
+		return 9
+	case PF5:
+		return 4
+	case PF6:
+		return 8
+	case PF7:
+		return 3
+	case PF8:
+		return 7
+	case PF9:
+		return 2
+	case PF10:
+		return 6
+	}
+	return 0
+}

src/machine/machine_stm32_bootloader.go

@@ -0,0 +1,9 @@
+//go:build stm32 && !stm32h7
+
+package machine
+
+// EnterBootloader resets the chip into the bootloader.
+// This is currently a stub for STM32, required to satisfy machine.EnterBootloader
+// called by machine/usb/cdc.
+func EnterBootloader() {
+}

src/machine/machine_stm32_exti_syscfg.go

@@ -1,4 +1,4 @@
-//go:build stm32 && !stm32f1 && !stm32l5 && !stm32wlx && !stm32g0 && !stm32u5 && !stm32u0
+//go:build stm32 && !stm32f1 && !stm32l5 && !stm32wlx && !stm32g0 && !stm32u5 && !stm32u0 && !stm32h7
 
 package machine
 

src/machine/machine_stm32_gpio_reva.go

@@ -1,4 +1,4 @@
-//go:build stm32 && !stm32l4 && !stm32l5 && !stm32wlx && !stm32g0 && !stm32u5 && !stm32u0
+//go:build stm32 && !stm32l4 && !stm32l5 && !stm32wlx && !stm32g0 && !stm32u5 && !stm32u0 && !stm32h7
 
 package machine
 

src/machine/machine_stm32_i2c_revb.go

@@ -1,4 +1,4 @@
-//go:build stm32l5 || stm32f7 || stm32l4 || stm32l0 || stm32wlx || stm32g0 || stm32u0 || stm32u5
+//go:build stm32l5 || stm32f7 || stm32l4 || stm32l0 || stm32wlx || stm32g0 || stm32u0 || stm32u5 || stm32h7
 
 package machine
 

src/machine/machine_stm32_moder_gpio.go

@@ -36,6 +36,9 @@ const (
 
 	// for PWM
 	PinModePWMOutput PinMode = 12
+
+	// for USB (DP/DM lines)
+	PinModeUSB PinMode = 13
 )
 
 // Define several bitfields that have different names across chip families but
@@ -144,6 +147,13 @@ func (p Pin) ConfigureAltFunc(config PinConfig, altFunc uint8) {
 		port.PUPDR.ReplaceBits(gpioPullFloating, gpioPullMask, pos)
 		p.SetAltFunc(altFunc)
 
+	// USB
+	case PinModeUSB:
+		port.MODER.ReplaceBits(gpioModeAlternate, gpioModeMask, pos)
+		port.OSPEEDR.ReplaceBits(gpioOutputSpeedVeryHigh, gpioOutputSpeedMask, pos)
+		port.PUPDR.ReplaceBits(gpioPullFloating, gpioPullMask, pos)
+		p.SetAltFunc(altFunc)
+
 	// ADC
 	case PinInputAnalog:
 		port.MODER.ReplaceBits(gpioModeAnalog, gpioModeMask, pos)

src/machine/machine_stm32_spi.go

@@ -1,4 +1,4 @@
-//go:build stm32 && !stm32f7x2 && !stm32l5x2 && !stm32g0 && !stm32u5 && !stm32u0
+//go:build stm32 && !stm32f7x2 && !stm32l5x2 && !stm32g0 && !stm32u5 && !stm32u0 && !stm32h7
 
 package machine
 

src/machine/machine_stm32_tim.go

@@ -79,6 +79,25 @@ func (t *TIM) Count() uint32 {
 	return uint32(t.Device.CNT.Get())
 }
 
+// SetOnePulseMode enables or disables the one-pulse mode.
+// When enabled, the timer will automatically stop at the next update event.
+func (t *TIM) SetOnePulseMode(enable bool) {
+	if enable {
+		t.Device.CR1.SetBits(stm32.TIM_CR1_OPM)
+	} else {
+		t.Device.CR1.ClearBits(stm32.TIM_CR1_OPM)
+	}
+}
+
+// SetEnabled enables or disables the timer.
+func (t *TIM) SetEnabled(enable bool) {
+	if enable {
+		t.Device.CR1.SetBits(stm32.TIM_CR1_CEN)
+	} else {
+		t.Device.CR1.ClearBits(stm32.TIM_CR1_CEN)
+	}
+}
+
 // SetWraparoundInterrupt configures a callback to be called each
 // time the timer 'wraps-around'.
 //

src/machine/machine_stm32h7.go

@@ -0,0 +1,558 @@
+//go:build stm32 && stm32h7
+
+package machine
+
+import (
+	"device/arm"
+	"device/stm32"
+	"runtime/interrupt"
+	"runtime/volatile"
+	"unsafe"
+)
+
+var deviceIDAddr = []uintptr{0x1FF1E800, 0x1FF1E804, 0x1FF1E808}
+
+// Default USB identifiers; board files with USB support should override these.
+const (
+	usb_STRING_PRODUCT      = "STM32H7"
+	usb_STRING_MANUFACTURER = "TinyGo"
+
+	usb_VID uint16 = 0x239A
+	usb_PID uint16 = 0x0001
+)
+
+// EnterBootloader resets the chip. Jumping to the H7 system bootloader
+// (0x1FF09800) is not implemented; a plain reset restarts the application.
+func EnterBootloader() {
+	arm.SystemReset()
+}
+
+// HSI_KER_FREQ is the fixed-frequency internal RC oscillator (RM0433 §8.2),
+// unaffected by the board's HSE crystal.
+const HSI_KER_FREQ = 64_000_000
+
+// sysClockFreq returns SYSCLK (PLL1P output) for the board's configured
+// xtalHz, per the M/N/P dividers initCLK() programs into PLL1.
+func sysClockFreq() uint32 {
+	pll := PLLParams400MHz()
+	return xtalHz / pll.M * pll.N / pll.P
+}
+
+// pll1QFreq returns the PLL1Q output (SPI1/2/3 kernel clock source).
+func pll1QFreq() uint32 {
+	pll := PLLParams400MHz()
+	return xtalHz / pll.M * pll.N / pll.Q
+}
+
+// hclkFreq, pclk1Freq..pclk4Freq return the AHB/APBx bus clocks. initCLK()
+// hardcodes HPRE/D2PPRE1/D2PPRE2/D1PPRE/D3PPRE to Div2, so these are fixed
+// ratios of SYSCLK regardless of xtal.
+func hclkFreq() uint32  { return sysClockFreq() / 2 }
+func pclk1Freq() uint32 { return hclkFreq() / 2 }
+func pclk2Freq() uint32 { return hclkFreq() / 2 }
+func pclk3Freq() uint32 { return hclkFreq() / 2 }
+func pclk4Freq() uint32 { return hclkFreq() / 2 }
+
+// Peripheral kernel clocks as configured by initCLK().
+func spi123KerFreq() uint32       { return pll1QFreq() } // D2CCIP1R.SPI123SEL = PLL1_Q
+func spi45KerFreq() uint32        { return pclk2Freq() } // D2CCIP1R.SPI45SEL  = APB
+func spi6KerFreq() uint32         { return pclk4Freq() } // D3CCIPR.SPI6SEL    = PCLK4
+const I2C_KER_FREQ = HSI_KER_FREQ // D2CCIP2R.I2C123SEL = HSI_KER
+
+func CPUFrequency() uint32 {
+	return sysClockFreq()
+}
+
+// initRNG gates the AHB2 bus clock for the RNG and enables the peripheral.
+// HSI48 is started and selected as the RNG kernel clock in initCLK().
+func initRNG() {
+	stm32.RCC.AHB2ENR.SetBits(stm32.RCC_AHB2ENR_RNGEN)
+	stm32.RNG.CR.SetBits(stm32.RNG_CR_RNGEN)
+}
+
+// Alternate function pin selection.
+const (
+	AF0_SYSTEM                          = 0
+	AF1_TIM1_2_16_17_HRTIM              = 1
+	AF2_TIM3_4_5_HRTIM                  = 2
+	AF3_TIM8_LPTIM1_DFSDM_HRTIM         = 3
+	AF4_I2C1_2_3_4_USART1               = 4
+	AF5_SPI1_2_3_4_5_6_I2S              = 5
+	AF6_SPI2_3_SAI1_I2S_UART4_DFSDM     = 6
+	AF7_SPI2_3_USART1_2_3_UART5_SPDIFRX = 7
+	AF8_SAI2_UART4_5_8_SPDIFRX_LPUART   = 8
+	AF9_FDCAN1_2_TIM13_14_QUADSPI_FMC   = 9
+	AF10_OTG_HS_FS_SAI2_QUADSPI_SDMMC2  = 10
+	AF11_SDMMC2_ETH_MDIO_UART7_SWPMI    = 11
+	AF12_FMC_SDMMC1_MDIOS_OTG_FS_UART7  = 12
+	AF13_DCMI_DSI_COMP_LTDC             = 13
+	AF14_LTDC                           = 14
+	AF15_EVENTOUT                       = 15
+)
+
+// Timer clock = 2×PCLK when both HPRE and PPREx prescalers are active (RM0433 §8.5.5).
+func apb1TimFreq() uint64 { return 2 * uint64(pclk1Freq()) }
+func apb2TimFreq() uint64 { return 2 * uint64(pclk2Freq()) }
+
+//---------- Timer related code
+
+var (
+	TIM1 = TIM{
+		EnableRegister: &stm32.RCC.APB2ENR,
+		EnableFlag:     stm32.RCC_APB2ENR_TIM1EN,
+		Device:         stm32.TIM1,
+		Channels: [4]TimerChannel{
+			TimerChannel{Pins: []PinFunction{{PA8, AF1_TIM1_2_16_17_HRTIM}, {PE9, AF1_TIM1_2_16_17_HRTIM}}},
+			TimerChannel{Pins: []PinFunction{{PA9, AF1_TIM1_2_16_17_HRTIM}, {PE11, AF1_TIM1_2_16_17_HRTIM}}},
+			TimerChannel{Pins: []PinFunction{{PA10, AF1_TIM1_2_16_17_HRTIM}, {PE13, AF1_TIM1_2_16_17_HRTIM}}},
+			TimerChannel{Pins: []PinFunction{{PA11, AF1_TIM1_2_16_17_HRTIM}, {PE14, AF1_TIM1_2_16_17_HRTIM}}},
+		},
+		busFreq: apb2TimFreq(),
+	}
+
+	TIM2 = TIM{
+		EnableRegister: &stm32.RCC.APB1LENR,
+		EnableFlag:     stm32.RCC_APB1LENR_TIM2EN,
+		Device:         stm32.TIM2,
+		Channels: [4]TimerChannel{
+			TimerChannel{Pins: []PinFunction{{PA0, AF1_TIM1_2_16_17_HRTIM}, {PA5, AF1_TIM1_2_16_17_HRTIM}, {PA15, AF1_TIM1_2_16_17_HRTIM}}},
+			TimerChannel{Pins: []PinFunction{{PA1, AF1_TIM1_2_16_17_HRTIM}, {PB3, AF1_TIM1_2_16_17_HRTIM}}},
+			TimerChannel{Pins: []PinFunction{{PA2, AF1_TIM1_2_16_17_HRTIM}, {PB10, AF1_TIM1_2_16_17_HRTIM}}},
+			TimerChannel{Pins: []PinFunction{{PA3, AF1_TIM1_2_16_17_HRTIM}, {PB11, AF1_TIM1_2_16_17_HRTIM}}},
+		},
+		busFreq: apb1TimFreq(),
+	}
+
+	TIM3 = TIM{
+		EnableRegister: &stm32.RCC.APB1LENR,
+		EnableFlag:     stm32.RCC_APB1LENR_TIM3EN,
+		Device:         stm32.TIM3,
+		Channels: [4]TimerChannel{
+			TimerChannel{Pins: []PinFunction{}},
+			TimerChannel{Pins: []PinFunction{}},
+			TimerChannel{Pins: []PinFunction{}},
+			TimerChannel{Pins: []PinFunction{}},
+		},
+		busFreq: apb1TimFreq(),
+	}
+
+	TIM4 = TIM{
+		EnableRegister: &stm32.RCC.APB1LENR,
+		EnableFlag:     stm32.RCC_APB1LENR_TIM4EN,
+		Device:         stm32.TIM4,
+		Channels: [4]TimerChannel{
+			TimerChannel{Pins: []PinFunction{{PB6, AF2_TIM3_4_5_HRTIM}, {PD12, AF2_TIM3_4_5_HRTIM}}},
+			TimerChannel{Pins: []PinFunction{{PB7, AF2_TIM3_4_5_HRTIM}, {PD13, AF2_TIM3_4_5_HRTIM}}},
+			TimerChannel{Pins: []PinFunction{{PB8, AF2_TIM3_4_5_HRTIM}, {PD14, AF2_TIM3_4_5_HRTIM}}},
+			TimerChannel{Pins: []PinFunction{{PB9, AF2_TIM3_4_5_HRTIM}, {PD15, AF2_TIM3_4_5_HRTIM}}},
+		},
+		busFreq: apb1TimFreq(),
+	}
+
+	TIM5 = TIM{
+		EnableRegister: &stm32.RCC.APB1LENR,
+		EnableFlag:     stm32.RCC_APB1LENR_TIM5EN,
+		Device:         stm32.TIM5,
+		Channels: [4]TimerChannel{
+			TimerChannel{Pins: []PinFunction{{PA0, AF2_TIM3_4_5_HRTIM}, {PH10, AF2_TIM3_4_5_HRTIM}}},
+			TimerChannel{Pins: []PinFunction{{PA1, AF2_TIM3_4_5_HRTIM}, {PH11, AF2_TIM3_4_5_HRTIM}}},
+			TimerChannel{Pins: []PinFunction{{PA2, AF2_TIM3_4_5_HRTIM}, {PH12, AF2_TIM3_4_5_HRTIM}}},
+			TimerChannel{Pins: []PinFunction{{PA3, AF2_TIM3_4_5_HRTIM}, {PI0, AF2_TIM3_4_5_HRTIM}}},
+		},
+		busFreq: apb1TimFreq(),
+	}
+
+	TIM8 = TIM{
+		EnableRegister: &stm32.RCC.APB2ENR,
+		EnableFlag:     stm32.RCC_APB2ENR_TIM8EN,
+		Device:         stm32.TIM8,
+		Channels: [4]TimerChannel{
+			TimerChannel{Pins: []PinFunction{{PC6, AF3_TIM8_LPTIM1_DFSDM_HRTIM}, {PI5, AF3_TIM8_LPTIM1_DFSDM_HRTIM}}},
+			TimerChannel{Pins: []PinFunction{{PC7, AF3_TIM8_LPTIM1_DFSDM_HRTIM}, {PI6, AF3_TIM8_LPTIM1_DFSDM_HRTIM}}},
+			TimerChannel{Pins: []PinFunction{{PC8, AF3_TIM8_LPTIM1_DFSDM_HRTIM}, {PI7, AF3_TIM8_LPTIM1_DFSDM_HRTIM}}},
+			TimerChannel{Pins: []PinFunction{{PC9, AF3_TIM8_LPTIM1_DFSDM_HRTIM}, {PI2, AF3_TIM8_LPTIM1_DFSDM_HRTIM}}},
+		},
+		busFreq: apb2TimFreq(),
+	}
+)
+
+func (t *TIM) registerUPInterrupt() interrupt.Interrupt {
+	switch t {
+	case &TIM1:
+		return interrupt.New(stm32.IRQ_TIM1_UP, TIM1.handleUPInterrupt)
+	case &TIM2:
+		return interrupt.New(stm32.IRQ_TIM2, TIM2.handleUPInterrupt)
+	case &TIM3:
+		return interrupt.New(stm32.IRQ_TIM3, TIM3.handleUPInterrupt)
+	case &TIM4:
+		return interrupt.New(stm32.IRQ_TIM4, TIM4.handleUPInterrupt)
+	case &TIM5:
+		return interrupt.New(stm32.IRQ_TIM5, TIM5.handleUPInterrupt)
+	case &TIM8:
+		return interrupt.New(stm32.IRQ_TIM8_UP_TIM13, TIM8.handleUPInterrupt)
+	}
+	return interrupt.Interrupt{}
+}
+
+func (t *TIM) registerOCInterrupt() interrupt.Interrupt {
+	switch t {
+	case &TIM1:
+		return interrupt.New(stm32.IRQ_TIM_CC, TIM1.handleOCInterrupt)
+	case &TIM2:
+		return interrupt.New(stm32.IRQ_TIM2, TIM2.handleOCInterrupt)
+	case &TIM3:
+		return interrupt.New(stm32.IRQ_TIM3, TIM3.handleOCInterrupt)
+	case &TIM4:
+		return interrupt.New(stm32.IRQ_TIM4, TIM4.handleOCInterrupt)
+	case &TIM5:
+		return interrupt.New(stm32.IRQ_TIM5, TIM5.handleOCInterrupt)
+	case &TIM8:
+		return interrupt.New(stm32.IRQ_TIM8_CC, TIM8.handleOCInterrupt)
+	}
+	return interrupt.Interrupt{}
+}
+
+func (t *TIM) enableMainOutput() {
+	if t.Device == stm32.TIM1 || t.Device == stm32.TIM8 {
+		t.Device.BDTR.SetBits(stm32.TIM_BDTR_MOE)
+	}
+}
+
+type psctype = uint32
+type arrtype = uint32
+type arrRegType = volatile.Register32
+
+const ARR_MAX = 0x10000
+const PSC_MAX = 0x10000
+
+//---------- UART related code
+
+// Configure the UART.
+func (uart *UART) configurePins(config UARTConfig) {
+	config.TX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTTX}, uart.TxAltFuncSelector)
+	config.RX.ConfigureAltFunc(PinConfig{Mode: PinModeUARTRX}, uart.RxAltFuncSelector)
+}
+
+func (uart *UART) getBaudRateDivisor(baudRate uint32) uint32 {
+	// Default USART kernel clock is the peripheral's own APB clock:
+	// USART1/6 sit on APB2, the rest on APB1.
+	clock := pclk1Freq()
+	if uart.Bus == stm32.USART1 || uart.Bus == stm32.USART6 {
+		clock = pclk2Freq()
+	}
+	return clock / baudRate
+}
+
+func (uart *UART) setRegisters() {
+	uart.rxReg = &uart.Bus.RDR
+	uart.txReg = &uart.Bus.TDR
+	uart.statusReg = &uart.Bus.ISR
+	uart.txEmptyFlag = stm32.USART_ISR_TXE
+	uart.errClearReg = &uart.Bus.ICR
+}
+
+func enableAltFuncClock(bus unsafe.Pointer) {
+	switch bus {
+	case unsafe.Pointer(stm32.USART1):
+		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_USART1EN)
+	case unsafe.Pointer(stm32.USART2):
+		stm32.RCC.APB1LENR.SetBits(stm32.RCC_APB1LENR_USART2EN)
+	case unsafe.Pointer(stm32.USART3):
+		stm32.RCC.APB1LENR.SetBits(stm32.RCC_APB1LENR_USART3EN)
+	case unsafe.Pointer(stm32.UART4):
+		stm32.RCC.APB1LENR.SetBits(stm32.RCC_APB1LENR_UART4EN)
+	case unsafe.Pointer(stm32.UART5):
+		stm32.RCC.APB1LENR.SetBits(stm32.RCC_APB1LENR_UART5EN)
+	case unsafe.Pointer(stm32.USART6):
+		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_USART6EN)
+	case unsafe.Pointer(stm32.UART7):
+		stm32.RCC.APB1LENR.SetBits(stm32.RCC_APB1LENR_UART7EN)
+	case unsafe.Pointer(stm32.UART8):
+		stm32.RCC.APB1LENR.SetBits(stm32.RCC_APB1LENR_UART8EN)
+	case unsafe.Pointer(stm32.LPUART1):
+		stm32.RCC.APB4ENR.SetBits(stm32.RCC_APB4ENR_LPUART1EN)
+	case unsafe.Pointer(stm32.I2C1):
+		stm32.RCC.APB1LENR.SetBits(stm32.RCC_APB1LENR_I2C1EN)
+	case unsafe.Pointer(stm32.I2C2):
+		stm32.RCC.APB1LENR.SetBits(stm32.RCC_APB1LENR_I2C2EN)
+	case unsafe.Pointer(stm32.I2C3):
+		stm32.RCC.APB1LENR.SetBits(stm32.RCC_APB1LENR_I2C3EN)
+	case unsafe.Pointer(stm32.I2C4):
+		stm32.RCC.APB4ENR.SetBits(stm32.RCC_APB4ENR_I2C4EN)
+	case unsafe.Pointer(stm32.SPI1):
+		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_SPI1EN)
+	case unsafe.Pointer(stm32.SPI2):
+		stm32.RCC.APB1LENR.SetBits(stm32.RCC_APB1LENR_SPI2EN)
+	case unsafe.Pointer(stm32.SPI3):
+		stm32.RCC.APB1LENR.SetBits(stm32.RCC_APB1LENR_SPI3EN)
+	case unsafe.Pointer(stm32.SPI4):
+		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_SPI4EN)
+	case unsafe.Pointer(stm32.SPI5):
+		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_SPI5EN)
+	case unsafe.Pointer(stm32.SPI6):
+		stm32.RCC.APB4ENR.SetBits(stm32.RCC_APB4ENR_SPI6EN)
+	case unsafe.Pointer(stm32.WWDG):
+		stm32.RCC.APB3ENR.SetBits(stm32.RCC_APB3ENR_WWDG1EN)
+	}
+}
+
+//---------- GPIO related code
+
+func (p Pin) getPort() *stm32.GPIO_Type {
+	switch p / 16 {
+	case 0:
+		return stm32.GPIOA
+	case 1:
+		return stm32.GPIOB
+	case 2:
+		return stm32.GPIOC
+	case 3:
+		return stm32.GPIOD
+	case 4:
+		return stm32.GPIOE
+	case 5:
+		return stm32.GPIOF
+	case 6:
+		return stm32.GPIOG
+	case 7:
+		return stm32.GPIOH
+	case 8:
+		return stm32.GPIOI
+	case 9:
+		return stm32.GPIOJ
+	case 10:
+		return stm32.GPIOK
+	default:
+		panic("machine: unknown port")
+	}
+}
+
+func (p Pin) enableClock() {
+	switch p.getPort() {
+	case stm32.GPIOA:
+		stm32.RCC.AHB4ENR.SetBits(stm32.RCC_AHB4ENR_GPIOAEN)
+	case stm32.GPIOB:
+		stm32.RCC.AHB4ENR.SetBits(stm32.RCC_AHB4ENR_GPIOBEN)
+	case stm32.GPIOC:
+		stm32.RCC.AHB4ENR.SetBits(stm32.RCC_AHB4ENR_GPIOCEN)
+	case stm32.GPIOD:
+		stm32.RCC.AHB4ENR.SetBits(stm32.RCC_AHB4ENR_GPIODEN)
+	case stm32.GPIOE:
+		stm32.RCC.AHB4ENR.SetBits(stm32.RCC_AHB4ENR_GPIOEEN)
+	case stm32.GPIOF:
+		stm32.RCC.AHB4ENR.SetBits(stm32.RCC_AHB4ENR_GPIOFEN)
+	case stm32.GPIOG:
+		stm32.RCC.AHB4ENR.SetBits(stm32.RCC_AHB4ENR_GPIOGEN)
+	case stm32.GPIOH:
+		stm32.RCC.AHB4ENR.SetBits(stm32.RCC_AHB4ENR_GPIOHEN)
+	case stm32.GPIOI:
+		stm32.RCC.AHB4ENR.SetBits(stm32.RCC_AHB4ENR_GPIOIEN)
+	case stm32.GPIOJ:
+		stm32.RCC.AHB4ENR.SetBits(stm32.RCC_AHB4ENR_GPIOJEN)
+	case stm32.GPIOK:
+		stm32.RCC.AHB4ENR.SetBits(stm32.RCC_AHB4ENR_GPIOKEN)
+	}
+}
+
+const (
+	PA0  = portA + 0
+	PA1  = portA + 1
+	PA2  = portA + 2
+	PA3  = portA + 3
+	PA4  = portA + 4
+	PA5  = portA + 5
+	PA6  = portA + 6
+	PA7  = portA + 7
+	PA8  = portA + 8
+	PA9  = portA + 9
+	PA10 = portA + 10
+	PA11 = portA + 11
+	PA12 = portA + 12
+	PA13 = portA + 13
+	PA14 = portA + 14
+	PA15 = portA + 15
+
+	PB0  = portB + 0
+	PB1  = portB + 1
+	PB2  = portB + 2
+	PB3  = portB + 3
+	PB4  = portB + 4
+	PB5  = portB + 5
+	PB6  = portB + 6
+	PB7  = portB + 7
+	PB8  = portB + 8
+	PB9  = portB + 9
+	PB10 = portB + 10
+	PB11 = portB + 11
+	PB12 = portB + 12
+	PB13 = portB + 13
+	PB14 = portB + 14
+	PB15 = portB + 15
+
+	PC0  = portC + 0
+	PC1  = portC + 1
+	PC2  = portC + 2
+	PC3  = portC + 3
+	PC4  = portC + 4
+	PC5  = portC + 5
+	PC6  = portC + 6
+	PC7  = portC + 7
+	PC8  = portC + 8
+	PC9  = portC + 9
+	PC10 = portC + 10
+	PC11 = portC + 11
+	PC12 = portC + 12
+	PC13 = portC + 13
+	PC14 = portC + 14
+	PC15 = portC + 15
+
+	PD0  = portD + 0
+	PD1  = portD + 1
+	PD2  = portD + 2
+	PD3  = portD + 3
+	PD4  = portD + 4
+	PD5  = portD + 5
+	PD6  = portD + 6
+	PD7  = portD + 7
+	PD8  = portD + 8
+	PD9  = portD + 9
+	PD10 = portD + 10
+	PD11 = portD + 11
+	PD12 = portD + 12
+	PD13 = portD + 13
+	PD14 = portD + 14
+	PD15 = portD + 15
+
+	PE0  = portE + 0
+	PE1  = portE + 1
+	PE2  = portE + 2
+	PE3  = portE + 3
+	PE4  = portE + 4
+	PE5  = portE + 5
+	PE6  = portE + 6
+	PE7  = portE + 7
+	PE8  = portE + 8
+	PE9  = portE + 9
+	PE10 = portE + 10
+	PE11 = portE + 11
+	PE12 = portE + 12
+	PE13 = portE + 13
+	PE14 = portE + 14
+	PE15 = portE + 15
+
+	PF0  = portF + 0
+	PF1  = portF + 1
+	PF2  = portF + 2
+	PF3  = portF + 3
+	PF4  = portF + 4
+	PF5  = portF + 5
+	PF6  = portF + 6
+	PF7  = portF + 7
+	PF8  = portF + 8
+	PF9  = portF + 9
+	PF10 = portF + 10
+	PF11 = portF + 11
+	PF12 = portF + 12
+	PF13 = portF + 13
+	PF14 = portF + 14
+	PF15 = portF + 15
+
+	PG0  = portG + 0
+	PG1  = portG + 1
+	PG2  = portG + 2
+	PG3  = portG + 3
+	PG4  = portG + 4
+	PG5  = portG + 5
+	PG6  = portG + 6
+	PG7  = portG + 7
+	PG8  = portG + 8
+	PG9  = portG + 9
+	PG10 = portG + 10
+	PG11 = portG + 11
+	PG12 = portG + 12
+	PG13 = portG + 13
+	PG14 = portG + 14
+	PG15 = portG + 15
+
+	PH0  = portH + 0
+	PH1  = portH + 1
+	PH2  = portH + 2
+	PH3  = portH + 3
+	PH4  = portH + 4
+	PH5  = portH + 5
+	PH6  = portH + 6
+	PH7  = portH + 7
+	PH8  = portH + 8
+	PH9  = portH + 9
+	PH10 = portH + 10
+	PH11 = portH + 11
+	PH12 = portH + 12
+	PH13 = portH + 13
+	PH14 = portH + 14
+	PH15 = portH + 15
+
+	PI0  = portI + 0
+	PI1  = portI + 1
+	PI2  = portI + 2
+	PI3  = portI + 3
+	PI4  = portI + 4
+	PI5  = portI + 5
+	PI6  = portI + 6
+	PI7  = portI + 7
+	PI8  = portI + 8
+	PI9  = portI + 9
+	PI10 = portI + 10
+	PI11 = portI + 11
+	PI12 = portI + 12
+	PI13 = portI + 13
+	PI14 = portI + 14
+	PI15 = portI + 15
+
+	PJ0  = portJ + 0
+	PJ1  = portJ + 1
+	PJ2  = portJ + 2
+	PJ3  = portJ + 3
+	PJ4  = portJ + 4
+	PJ5  = portJ + 5
+	PJ6  = portJ + 6
+	PJ7  = portJ + 7
+	PJ8  = portJ + 8
+	PJ9  = portJ + 9
+	PJ10 = portJ + 10
+	PJ11 = portJ + 11
+	PJ12 = portJ + 12
+	PJ13 = portJ + 13
+	PJ14 = portJ + 14
+	PJ15 = portJ + 15
+
+	PK0 = portK + 0
+	PK1 = portK + 1
+	PK2 = portK + 2
+	PK3 = portK + 3
+	PK4 = portK + 4
+	PK5 = portK + 5
+	PK6 = portK + 6
+	PK7 = portK + 7
+)
+
+//---------- I2C related code
+
+// getFreqRange returns the TIMINGR value for the given I2C frequency.
+// Values are for HSI_KER=64MHz (configured in initCLK).
+// Derived from ST I2C timing calculator.
+func (i2c *I2C) getFreqRange(br uint32) uint32 {
+	switch br {
+	case 10 * KHz:
+		return 0x30E0E7CF
+	case 100 * KHz:
+		return 0x10B0BFCF
+	case 400 * KHz:
+		return 0x00901E74
+	case 800 * KHz:
+		return 0x00401137
+	case 1_000 * KHz:
+		return 0x00401028
+	default:
+		return 0x10B0BFCF
+	}
+}

src/machine/machine_stm32h7_cache.go

@@ -0,0 +1,57 @@
+//go:build stm32 && stm32h7
+
+package machine
+
+import (
+	"device/arm"
+	"runtime/volatile"
+	"unsafe"
+)
+
+// Cortex-M7 cache maintenance by-address registers (ARMv7-M ARM Table B3-7).
+var (
+	scbDCIMVAC  = (*volatile.Register32)(unsafe.Pointer(uintptr(0xE000EF5C))) // Invalidate D-cache line by address (W)
+	scbDCCMVAC  = (*volatile.Register32)(unsafe.Pointer(uintptr(0xE000EF68))) // Clean D-cache line by address (W)
+	scbDCCIMVAC = (*volatile.Register32)(unsafe.Pointer(uintptr(0xE000EF70))) // Clean+Invalidate D-cache line by address (W)
+)
+
+const dCacheLineSize = 32 // bytes; fixed on Cortex-M7
+
+// DCacheClean writes dirty cache lines covering [addr, addr+size) back to
+// memory without invalidating them. Call before the CPU hands a buffer to a
+// DMA controller that only reads the buffer.
+func DCacheClean(addr uintptr, size uintptr) {
+	arm.Asm("dsb 0xF")
+	end := addr + size
+	for a := addr &^ (dCacheLineSize - 1); a < end; a += dCacheLineSize {
+		scbDCCMVAC.Set(uint32(a))
+	}
+	arm.Asm("dsb 0xF")
+	arm.Asm("isb 0xF")
+}
+
+// DCacheInvalidate marks cache lines covering [addr, addr+size) as invalid so
+// the next access re-fetches from memory. Call after a DMA write completes
+// before the CPU reads the buffer.
+func DCacheInvalidate(addr uintptr, size uintptr) {
+	arm.Asm("dsb 0xF")
+	end := addr + size
+	for a := addr &^ (dCacheLineSize - 1); a < end; a += dCacheLineSize {
+		scbDCIMVAC.Set(uint32(a))
+	}
+	arm.Asm("dsb 0xF")
+	arm.Asm("isb 0xF")
+}
+
+// DCacheFlush cleans and invalidates cache lines covering [addr, addr+size).
+// Use when the region is both written by the CPU and read by DMA (or vice
+// versa) and you want to synchronize in a single pass.
+func DCacheFlush(addr uintptr, size uintptr) {
+	arm.Asm("dsb 0xF")
+	end := addr + size
+	for a := addr &^ (dCacheLineSize - 1); a < end; a += dCacheLineSize {
+		scbDCCIMVAC.Set(uint32(a))
+	}
+	arm.Asm("dsb 0xF")
+	arm.Asm("isb 0xF")
+}

src/machine/machine_stm32h7_exti.go

@@ -0,0 +1,27 @@
+//go:build stm32 && stm32h7
+
+package machine
+
+import (
+	"device/stm32"
+	"runtime/volatile"
+)
+
+func getEXTIConfigRegister(pin uint8) *volatile.Register32 {
+	switch (pin & 0xf) / 4 {
+	case 0:
+		return &stm32.SYSCFG.EXTICR1
+	case 1:
+		return &stm32.SYSCFG.EXTICR2
+	case 2:
+		return &stm32.SYSCFG.EXTICR3
+	case 3:
+		return &stm32.SYSCFG.EXTICR4
+	}
+	return nil
+}
+
+func enableEXTIConfigRegisters() {
+	// Enable SYSCFG in APB4ENR
+	stm32.RCC.APB4ENR.SetBits(stm32.RCC_APB4ENR_SYSCFGEN)
+}

src/machine/machine_stm32h7_gpio.go

@@ -0,0 +1,111 @@
+//go:build stm32 && stm32h7
+
+package machine
+
+import (
+	"device/stm32"
+	"runtime/interrupt"
+)
+
+// Callbacks for pin interrupt events
+var pinCallbacks [16]func(Pin)
+
+// The pin currently associated with interrupt callback
+// for a given slot.
+var interruptPins [16]Pin
+
+// SetInterrupt sets an interrupt to be executed when a particular pin changes
+// state. The pin should already be configured as an input, including a pull up
+// or down if no external pull is provided.
+func (p Pin) SetInterrupt(change PinChange, callback func(Pin)) error {
+	port := uint32(uint8(p) / 16)
+	pin := uint8(p) % 16
+
+	enableEXTIConfigRegisters()
+
+	if callback == nil {
+		stm32.EXTI.CPUIMR1.ClearBits(1 << pin)
+		pinCallbacks[pin] = nil
+		return nil
+	}
+
+	if pinCallbacks[pin] != nil {
+		return ErrNoPinChangeChannel
+	}
+
+	pinCallbacks[pin] = callback
+	interruptPins[pin] = p
+
+	crReg := getEXTIConfigRegister(pin)
+	shift := (pin & 0x3) * 4
+	crReg.ReplaceBits(port, 0xf, shift)
+
+	if (change & PinRising) != 0 {
+		stm32.EXTI.RTSR1.SetBits(1 << pin)
+	}
+	if (change & PinFalling) != 0 {
+		stm32.EXTI.FTSR1.SetBits(1 << pin)
+	}
+	stm32.EXTI.CPUIMR1.SetBits(1 << pin)
+
+	intr := p.registerInterrupt()
+	intr.SetPriority(0)
+	intr.Enable()
+
+	return nil
+}
+
+func (p Pin) registerInterrupt() interrupt.Interrupt {
+	pin := uint8(p) % 16
+	switch pin {
+	case 0:
+		return interrupt.New(stm32.IRQ_EXTI0, handlePinInterrupt0)
+	case 1:
+		return interrupt.New(stm32.IRQ_EXTI1, handlePinInterrupt1)
+	case 2:
+		return interrupt.New(stm32.IRQ_EXTI2, handlePinInterrupt2)
+	case 3:
+		return interrupt.New(stm32.IRQ_EXTI3, handlePinInterrupt3)
+	case 4:
+		return interrupt.New(stm32.IRQ_EXTI4, handlePinInterrupt4)
+	case 5, 6, 7, 8, 9:
+		return interrupt.New(stm32.IRQ_EXTI9_5, handlePinInterrupt9_5)
+	case 10, 11, 12, 13, 14, 15:
+		return interrupt.New(stm32.IRQ_EXTI15_10, handlePinInterrupt15_10)
+	}
+	return interrupt.Interrupt{}
+}
+
+func handlePinInterrupt0(interrupt.Interrupt) { handlePinInterrupt(0) }
+func handlePinInterrupt1(interrupt.Interrupt) { handlePinInterrupt(1) }
+func handlePinInterrupt2(interrupt.Interrupt) { handlePinInterrupt(2) }
+func handlePinInterrupt3(interrupt.Interrupt) { handlePinInterrupt(3) }
+func handlePinInterrupt4(interrupt.Interrupt) { handlePinInterrupt(4) }
+func handlePinInterrupt9_5(interrupt.Interrupt) {
+	handlePinInterrupt(5)
+	handlePinInterrupt(6)
+	handlePinInterrupt(7)
+	handlePinInterrupt(8)
+	handlePinInterrupt(9)
+}
+func handlePinInterrupt15_10(interrupt.Interrupt) {
+	handlePinInterrupt(10)
+	handlePinInterrupt(11)
+	handlePinInterrupt(12)
+	handlePinInterrupt(13)
+	handlePinInterrupt(14)
+	handlePinInterrupt(15)
+}
+
+func handlePinInterrupt(pin uint8) {
+	if stm32.EXTI.CPUPR1.HasBits(1 << pin) {
+		// Writing 1 to the pending register clears the
+		// pending flag for that bit
+		stm32.EXTI.CPUPR1.Set(1 << pin)
+
+		callback := pinCallbacks[pin]
+		if callback != nil {
+			callback(interruptPins[pin])
+		}
+	}
+}

src/machine/machine_stm32h7_hsem.go

@@ -0,0 +1,173 @@
+//go:build stm32 && stm32h753
+
+package machine
+
+import (
+	"device/stm32"
+	"runtime/volatile"
+	"unsafe"
+)
+
+var (
+	HSEM_CORE1 = (*HSEM_CORE_Type)(unsafe.Pointer((uintptr(unsafe.Pointer(stm32.HSEM)) + 0x100)))
+	HSEM_CORE2 = (*HSEM_CORE_Type)(unsafe.Pointer((uintptr(unsafe.Pointer(stm32.HSEM)) + 0x110)))
+)
+
+// HSEM_CORE represents the registers for a core's hardware semaphore interrupts.
+type HSEM_CORE_Type struct {
+	IER  volatile.Register32 // HSEM Interrupt enable register         Address offset: HSEM + 0x100 + n*0x10 (Interrupt N (0 or 1))
+	ICR  volatile.Register32 // HSEM Interrupt clear register          Address offset: HSEM + 0x104 + n*0x10 (Interrupt N (0 or 1))
+	ISR  volatile.Register32 // HSEM Interrupt Status register         Address offset: HSEM + 0x108 + n*0x10 (Interrupt N (0 or 1))
+	MISR volatile.Register32 // HSEM Interrupt Masked Status register  Address offset: HSEM + 0x10C + n*0x10 (Interrupt N (0 or 1))
+}
+
+type HSEM_ID_Type uint8
+
+// Lock performs a 1-step (read) lock on the receiver semaphore ID.
+// Semaphores can be used to ensure synchronization between processes running on
+// different cores. Lock provides a non-blocking mechanism to lock semaphores
+// in an atomic way.
+// Returns true if and only if the semaphore lock is acquired or the given core
+// already has the semaphore locked.
+func (id HSEM_ID_Type) Lock(core uint32) bool {
+	switch id {
+	case 0:
+		return stm32.HSEM.RLR0.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 1:
+		return stm32.HSEM.RLR1.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 2:
+		return stm32.HSEM.RLR2.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 3:
+		return stm32.HSEM.RLR3.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 4:
+		return stm32.HSEM.RLR4.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 5:
+		return stm32.HSEM.RLR5.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 6:
+		return stm32.HSEM.RLR6.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 7:
+		return stm32.HSEM.RLR7.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 8:
+		return stm32.HSEM.RLR8.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 9:
+		return stm32.HSEM.RLR9.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 10:
+		return stm32.HSEM.RLR10.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 11:
+		return stm32.HSEM.RLR11.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 12:
+		return stm32.HSEM.RLR12.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 13:
+		return stm32.HSEM.RLR13.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 14:
+		return stm32.HSEM.RLR14.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 15:
+		return stm32.HSEM.RLR15.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 16:
+		return stm32.HSEM.RLR16.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 17:
+		return stm32.HSEM.RLR17.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 18:
+		return stm32.HSEM.RLR18.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 19:
+		return stm32.HSEM.RLR19.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 20:
+		return stm32.HSEM.RLR20.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 21:
+		return stm32.HSEM.RLR21.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 22:
+		return stm32.HSEM.RLR22.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 23:
+		return stm32.HSEM.RLR23.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 24:
+		return stm32.HSEM.RLR24.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 25:
+		return stm32.HSEM.RLR25.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 26:
+		return stm32.HSEM.RLR26.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 27:
+		return stm32.HSEM.RLR27.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 28:
+		return stm32.HSEM.RLR28.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 29:
+		return stm32.HSEM.RLR29.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 30:
+		return stm32.HSEM.RLR30.Get() == (stm32.HSEM_RLR_LOCK | core)
+	case 31:
+		return stm32.HSEM.RLR31.Get() == (stm32.HSEM_RLR_LOCK | core)
+	}
+	return false
+}
+
+// Unlock releases the lock on the receiver semaphore ID.
+// Semaphores can be used to ensure synchronization between processes running on
+// different cores. Unlock provides a non-blocking mechanism to unlock
+// semaphores in an atomic way.
+func (id HSEM_ID_Type) Unlock(core uint32) {
+	switch id {
+	case 0:
+		stm32.HSEM.R0.Set(core)
+	case 1:
+		stm32.HSEM.R1.Set(core)
+	case 2:
+		stm32.HSEM.R2.Set(core)
+	case 3:
+		stm32.HSEM.R3.Set(core)
+	case 4:
+		stm32.HSEM.R4.Set(core)
+	case 5:
+		stm32.HSEM.R5.Set(core)
+	case 6:
+		stm32.HSEM.R6.Set(core)
+	case 7:
+		stm32.HSEM.R7.Set(core)
+	case 8:
+		stm32.HSEM.R8.Set(core)
+	case 9:
+		stm32.HSEM.R9.Set(core)
+	case 10:
+		stm32.HSEM.R10.Set(core)
+	case 11:
+		stm32.HSEM.R11.Set(core)
+	case 12:
+		stm32.HSEM.R12.Set(core)
+	case 13:
+		stm32.HSEM.R13.Set(core)
+	case 14:
+		stm32.HSEM.R14.Set(core)
+	case 15:
+		stm32.HSEM.R15.Set(core)
+	case 16:
+		stm32.HSEM.R16.Set(core)
+	case 17:
+		stm32.HSEM.R17.Set(core)
+	case 18:
+		stm32.HSEM.R18.Set(core)
+	case 19:
+		stm32.HSEM.R19.Set(core)
+	case 20:
+		stm32.HSEM.R20.Set(core)
+	case 21:
+		stm32.HSEM.R21.Set(core)
+	case 22:
+		stm32.HSEM.R22.Set(core)
+	case 23:
+		stm32.HSEM.R23.Set(core)
+	case 24:
+		stm32.HSEM.R24.Set(core)
+	case 25:
+		stm32.HSEM.R25.Set(core)
+	case 26:
+		stm32.HSEM.R26.Set(core)
+	case 27:
+		stm32.HSEM.R27.Set(core)
+	case 28:
+		stm32.HSEM.R28.Set(core)
+	case 29:
+		stm32.HSEM.R29.Set(core)
+	case 30:
+		stm32.HSEM.R30.Set(core)
+	case 31:
+		stm32.HSEM.R31.Set(core)
+	}
+}

src/machine/machine_stm32h7_pll.go

@@ -0,0 +1,46 @@
+//go:build stm32 && stm32h7
+
+package machine
+
+import "device/stm32"
+
+// PLLParams400MHz returns the HSE PLL dividers needed to reach a 800MHz VCO
+// (400MHz SYSCLK, P=2, Q=4) for the configured crystal frequency.
+// It returns the appropriate PLL1RGE range value in the R field.
+func PLLParams400MHz() PLLParams {
+	var m, n, rge uint32
+	switch xtalHz {
+	case 8_000_000:
+		m = 1
+		n = 100
+	case 16_000_000:
+		m = 2
+		n = 100
+	case 24_000_000:
+		m = 3
+		n = 100
+	case 25_000_000:
+		m = 5
+		n = 160
+	default:
+		panic("unsupported xtal frequency")
+	}
+
+	vcoIn := xtalHz / m
+	if vcoIn < 2_000_000 {
+		rge = stm32.RCC_PLLCFGR_PLL1RGE_Range1
+	} else if vcoIn < 4_000_000 {
+		rge = stm32.RCC_PLLCFGR_PLL1RGE_Range2
+	} else if vcoIn < 8_000_000 {
+		rge = stm32.RCC_PLLCFGR_PLL1RGE_Range4
+	} else {
+		rge = stm32.RCC_PLLCFGR_PLL1RGE_Range8
+	}
+
+	return PLLParams{M: m, N: n, P: 2, Q: 4, R: rge}
+}
+
+// HSEBypass returns whether the HSE clock is configured in bypass mode (external MCO clock).
+func HSEBypass() bool {
+	return hseBypass
+}

src/machine/machine_stm32h7_spi.go

@@ -0,0 +1,148 @@
+//go:build stm32 && stm32h7
+
+package machine
+
+// Peripheral abstraction layer for SPI on the stm32h7 family
+
+import (
+	"device/stm32"
+	"errors"
+	"math/bits"
+	"runtime/volatile"
+	"unsafe"
+)
+
+var errSPIOverrun = errors.New("SPI overrun or mode fault")
+
+type SPI struct {
+	Bus             *stm32.SPI_Type
+	AltFuncSelector uint8
+}
+
+// SPIConfig is used to store config info for SPI.
+type SPIConfig struct {
+	Frequency uint32
+	SCK       Pin
+	SDO       Pin
+	SDI       Pin
+	LSBFirst  bool
+	Mode      uint8
+}
+
+// Configure is intended to setup the STM32 SPI interface.
+func (spi *SPI) Configure(config SPIConfig) error {
+	// disable SPI interface before any configuration changes
+	spi.Bus.CR1.ClearBits(stm32.SPI_CR1_SPE)
+
+	// enable clock for SPI
+	enableAltFuncClock(unsafe.Pointer(spi.Bus))
+
+	// init pins
+	if config.SCK == 0 && config.SDO == 0 && config.SDI == 0 {
+		config.SCK = SPI0_SCK_PIN
+		config.SDO = SPI0_SDO_PIN
+		config.SDI = SPI0_SDI_PIN
+	}
+	spi.configurePins(config)
+
+	// CFG1 configuration: MBR and DSIZE (8-bit)
+	cfg1 := spi.getBaudRate(config)
+	cfg1 |= (8 - 1) << stm32.SPI_CFG1_DSIZE_Pos // 8-bit data size
+	spi.Bus.CFG1.Set(cfg1)
+
+	// CFG2 configuration: CPOL, CPHA, MASTER, SSM, COMM
+	var cfg2 uint32 = stm32.SPI_CFG2_MASTER // bit mask, not field value
+	cfg2 |= stm32.SPI_CFG2_SSM              // software NSS; bit mask, not field value
+
+	if config.LSBFirst {
+		cfg2 |= 1 << 23 // LSBFRST is bit 23 in CFG2
+	}
+
+	// set polarity and phase
+	switch config.Mode {
+	case Mode1:
+		cfg2 |= stm32.SPI_CFG2_CPHA_SecondEdge << stm32.SPI_CFG2_CPHA_Pos
+	case Mode2:
+		cfg2 |= stm32.SPI_CFG2_CPOL_IdleHigh << stm32.SPI_CFG2_CPOL_Pos
+	case Mode3:
+		cfg2 |= stm32.SPI_CFG2_CPOL_IdleHigh << stm32.SPI_CFG2_CPOL_Pos
+		cfg2 |= stm32.SPI_CFG2_CPHA_SecondEdge << stm32.SPI_CFG2_CPHA_Pos
+	}
+	spi.Bus.CFG2.Set(cfg2)
+
+	// CR2: TSIZE = 0 (Endless mode)
+	spi.Bus.CR2.Set(0)
+
+	// CR1: SPE and SSI (use bit masks, not field values)
+	spi.Bus.CR1.Set(stm32.SPI_CR1_SSI | stm32.SPI_CR1_SPE)
+
+	return nil
+}
+
+func (spi *SPI) config8Bits() {
+	// Already handled in Configure via DSIZE
+}
+
+func (spi *SPI) configurePins(config SPIConfig) {
+	config.SCK.ConfigureAltFunc(PinConfig{Mode: PinModeSPICLK}, spi.AltFuncSelector)
+	config.SDO.ConfigureAltFunc(PinConfig{Mode: PinModeSPISDO}, spi.AltFuncSelector)
+	config.SDI.ConfigureAltFunc(PinConfig{Mode: PinModeSPISDI}, spi.AltFuncSelector)
+}
+
+func (spi *SPI) getBaudRate(config SPIConfig) uint32 {
+	clock := spi45KerFreq()
+	if spi.Bus == stm32.SPI1 || spi.Bus == stm32.SPI2 || spi.Bus == stm32.SPI3 {
+		clock = spi123KerFreq()
+	} else if spi.Bus == stm32.SPI6 {
+		clock = spi6KerFreq()
+	}
+
+	if config.Frequency == 0 {
+		config.Frequency = clock / 2
+	}
+
+	// limit requested frequency to bus frequency and min frequency (DIV256)
+	freq := config.Frequency
+	if min := clock / 256; freq < min {
+		freq = min
+	} else if freq > clock/2 {
+		freq = clock / 2
+	}
+
+	// Round up to the next power-of-two divisor so output never exceeds freq.
+	// MBR encodes actual divider as 2^(MBR+1), so MBR = ceil_log2(ratio) - 1.
+	div := bits.Len32(clock/freq-1) - 1
+	if div > 7 {
+		div = 7
+	}
+
+	return uint32(div) << stm32.SPI_CFG1_MBR_Pos
+}
+
+// Transfer writes/reads a single byte using the SPI interface.
+func (spi *SPI) Transfer(w byte) (byte, error) {
+	// RM0433 §50.4.9: set CSTART before writing TXDR.
+	spi.Bus.CR1.SetBits(stm32.SPI_CR1_CSTART)
+
+	// Wait for TXP (Transmit packet space available)
+	for !spi.Bus.SR.HasBits(stm32.SPI_SR_TXP) {
+	}
+
+	// Write to TXDR as 8-bit access to push exactly one byte into the FIFO.
+	(*volatile.Register8)(unsafe.Pointer(&spi.Bus.TXDR.Reg)).Set(w)
+
+	// Wait for RXP (Receive packet available)
+	for !spi.Bus.SR.HasBits(stm32.SPI_SR_RXP) {
+	}
+
+	// Check for overrun or mode fault before reading, to avoid returning stale data.
+	if sr := spi.Bus.SR.Get(); sr&(stm32.SPI_SR_OVR|stm32.SPI_SR_MODF) != 0 {
+		spi.Bus.IFCR.SetBits(stm32.SPI_IFCR_OVRC | stm32.SPI_IFCR_MODFC)
+		return 0, errSPIOverrun
+	}
+
+	// Read from RXDR
+	data := byte(spi.Bus.RXDR.Get())
+
+	return data, nil
+}

src/machine/machine_stm32h7_usb.go

@@ -0,0 +1,560 @@
+//go:build stm32 && stm32h7
+
+package machine
+
+import (
+	"device/arm"
+	"device/stm32"
+	"machine/usb"
+	"runtime/interrupt"
+	"runtime/volatile"
+	"unsafe"
+)
+
+// Synopsys DesignWare OTG registers
+// The SVD-generated Go device file is missing some device-mode registers,
+// so we define them here based on the Synopsys OTG IP.
+type usbOTGRegs struct {
+	// Global registers (0x000)
+	GOTGCTL   volatile.Register32 // 0x00
+	GOTGINT   volatile.Register32 // 0x04
+	GAHBCFG   volatile.Register32 // 0x08
+	GUSBCFG   volatile.Register32 // 0xC
+	GRSTCTL   volatile.Register32 // 0x10
+	GINTSTS   volatile.Register32 // 0x14
+	GINTMSK   volatile.Register32 // 0x18
+	GRXSTSR   volatile.Register32 // 0x1C
+	GRXSTSP   volatile.Register32 // 0x20
+	GRXFSIZ   volatile.Register32 // 0x24
+	GNPTXFSIZ volatile.Register32 // 0x28
+	GNPTXSTS  volatile.Register32 // 0x2C
+	_         [8]byte
+	GCCFG     volatile.Register32 // 0x38
+	CID       volatile.Register32 // 0x3C
+	_         [20]byte
+	GLPMCFG   volatile.Register32 // 0x54
+	GPWRDN    volatile.Register32 // 0x58
+	_         [4]byte
+	GDFIFO_S  volatile.Register32 // 0x60
+	_         [156]byte
+	HPTXFSIZ  volatile.Register32     // 0x100
+	DIEPTXF   [15]volatile.Register32 // 0x104
+	_         [1728]byte
+
+	// Device registers (0x800)
+	DCFG       volatile.Register32 // 0x800
+	DCTL       volatile.Register32 // 0x804
+	DSTS       volatile.Register32 // 0x808
+	_          [4]byte
+	DIEPMSK    volatile.Register32 // 0x810
+	DOEPMSK    volatile.Register32 // 0x814
+	DAINT      volatile.Register32 // 0x818
+	DAINTMSK   volatile.Register32 // 0x81C
+	_          [32]byte
+	DIEPEMPMSK volatile.Register32 // 0x840
+	_          [188]byte
+
+	// Endpoint registers
+	INEP [16]struct {
+		CTL    volatile.Register32 // 0x900 + n*0x20
+		_      [4]byte
+		INT    volatile.Register32 // 0x908 + n*0x20
+		_      [4]byte
+		TSIZ   volatile.Register32 // 0x910 + n*0x20
+		DMA    volatile.Register32 // 0x914 + n*0x20
+		TXFSTS volatile.Register32 // 0x918 + n*0x20
+		_      [4]byte
+	}
+	OUTEP [16]struct {
+		CTL  volatile.Register32 // 0xB00 + n*0x20
+		_    [4]byte
+		INT  volatile.Register32 // 0xB08 + n*0x20
+		_    [4]byte
+		TSIZ volatile.Register32 // 0xB10 + n*0x20
+		DMA  volatile.Register32 // 0xB14 + n*0x20
+		_    [8]byte
+	}
+
+	_ [256]byte
+
+	// Power and clock gating registers (0xE00)
+	PCGCCTL volatile.Register32 // 0xE00
+}
+
+// USB2 OTG_FS: the FS-only core wired to PA11/PA12 (Nucleo CN13).
+// USB1 OTG_HS at 0x40040000 uses ULPI or its own embedded PHY on PB14/PB15,
+// which is NOT routed to the user USB connector on this board.
+var usbOTG = (*usbOTGRegs)(unsafe.Pointer(uintptr(0x40080000)))
+
+const (
+	// GUSBCFG bits
+	GUSBCFG_PHYSEL   = 1 << 6
+	GUSBCFG_TRDT_Pos = 10
+	GUSBCFG_FDMOD    = 1 << 30
+
+	// GAHBCFG bits
+	GAHBCFG_GINT = 1 << 0
+
+	// GRSTCTL bits
+	GRSTCTL_CSRST      = 1 << 0
+	GRSTCTL_RXFFLSH    = 1 << 4
+	GRSTCTL_TXFFLSH    = 1 << 5
+	GRSTCTL_TXFNUM_ALL = 0x10 << 6
+	GRSTCTL_AHBIDL     = 1 << 31
+
+	// GINTSTS / GINTMSK bits
+	GINT_RXFLVL   = 1 << 4
+	GINT_GINAKEFF = 1 << 6
+	GINT_GONAKEFF = 1 << 7
+	GINT_USBSUSP  = 1 << 11
+	GINT_USBRST   = 1 << 12
+	GINT_ENUMDNE  = 1 << 13
+	GINT_IEPINT   = 1 << 18
+	GINT_OEPINT   = 1 << 19
+
+	// DCFG bits
+	DCFG_DSPD_FS = 0x3 << 0
+
+	// DCTL bits
+	DCTL_RWUSIG = 1 << 0
+	DCTL_SDIS   = 1 << 1
+	DCTL_GINSTS = 1 << 2
+	DCTL_GONSTS = 1 << 3
+
+	// DIEPCTL / DOEPCTL bits
+	DEPCTL_MPSIZ_Pos  = 0
+	DEPCTL_USBAEP     = 1 << 15
+	DEPCTL_EPTYP_Pos  = 18
+	DEPCTL_STALL      = 1 << 21
+	DEPCTL_CNAK       = 1 << 26
+	DEPCTL_SNAK       = 1 << 27
+	DEPCTL_TXFNUM_Pos = 22
+	DEPCTL_EPDIS      = 1 << 30
+	DEPCTL_EPENA      = 1 << 31
+
+	// DIEPINT / DOEPINT bits
+	DEPINT_XFERC  = 1 << 0
+	DEPINT_EPDISD = 1 << 1
+	DEPINT_SETUP  = 1 << 3
+
+	NumberOfUSBEndpoints = 9
+
+	// FIFO layout in 32-bit words: shared RX FIFO plus one 64-word TX FIFO
+	// for EP0 and each of the 8 IN endpoints (256 + 9*64 = 832 ≤ 1024).
+	rxFIFOWords = 256
+	txFIFOWords = 64
+)
+
+var (
+	// ep0OutReceived signals that an OUT packet was received on EP0.
+	// Volatile: written from the USB interrupt, busy-waited on from thread mode.
+	ep0OutReceived volatile.Register8
+)
+
+// Configure the USB peripheral.
+func (dev *USBDevice) Configure(config UARTConfig) {
+	if dev.initcomplete {
+		return
+	}
+
+	// 1. Enable clocks
+	stm32.RCC.AHB1ENR.SetBits(stm32.RCC_AHB1ENR_USB2OTGHSEN)
+	// The FS core has no ULPI clock, but AHB1LPENR resets with
+	// USB2OTGULPILPEN set, so in CPU Sleep mode (the scheduler's WFE) the RCC
+	// waits on a ULPI clock that never comes and the core's AHB interface
+	// stalls, killing USB whenever the CPU sleeps.
+	// Keep the OTG bus clock running in Sleep, drop the ULPI one.
+	stm32.RCC.AHB1LPENR.SetBits(stm32.RCC_AHB1LPENR_USB2OTGLPEN)
+	stm32.RCC.AHB1LPENR.ClearBits(stm32.RCC_AHB1LPENR_USB2OTGULPILPEN)
+	// Enable USB regulator (USB33DEN) for internal PHY.
+	// Already done in initCLK, but setting here as well for safety.
+	stm32.PWR.CR3.SetBits(stm32.PWR_CR3_USB33DEN)
+
+	// Pulse RCC reset to clear any stale state from a warm reset.
+	stm32.RCC.AHB1RSTR.SetBits(stm32.RCC_AHB1RSTR_USB2OTGRST)
+	stm32.RCC.AHB1RSTR.ClearBits(stm32.RCC_AHB1RSTR_USB2OTGRST)
+
+	// 2. Setup pins (PA11=DM, PA12=DP) for USB2 OTG_FS — AF10.
+	PA11.ConfigureAltFunc(PinConfig{Mode: PinModeUSB}, AF10_OTG_HS_FS_SAI2_QUADSPI_SDMMC2)
+	PA12.ConfigureAltFunc(PinConfig{Mode: PinModeUSB}, AF10_OTG_HS_FS_SAI2_QUADSPI_SDMMC2)
+
+	// 3. Select internal FS PHY BEFORE the core reset below — the reset FSM
+	// samples the PHY clock, which only runs once PHYSEL is set. Give the
+	// clock a few cycles to start or CSRST can hang / self-clear too early.
+	usbOTG.GUSBCFG.SetBits(GUSBCFG_PHYSEL)
+	for j := 0; j < 10_000; j++ {
+		arm.Asm("nop")
+	}
+
+	// 4. Core Reset — wait for AHB idle then pulse CSRST.
+	for usbOTG.GRSTCTL.Get()&GRSTCTL_AHBIDL == 0 {
+	}
+	usbOTG.GRSTCTL.SetBits(GRSTCTL_CSRST)
+	for usbOTG.GRSTCTL.Get()&GRSTCTL_CSRST != 0 {
+	}
+
+	// Power up the FS transceiver AFTER the core reset: CSRST wipes GCCFG,
+	// so setting PWRDWN earlier leaves the transceiver off and the DP
+	// pull-up never appears (host sees no cable).
+	// No HW VBUS sensing: CN13's VBUS pin is not wired to the MCU VBUS-sense
+	// input on this board, so leave GCCFG.VBDEN (bit 21) clear and force
+	// session/VBUS valid via GOTGCTL instead (below).
+	usbOTG.GCCFG.Set(1 << 16) // PWRDWN
+
+	// Make sure the PHY clock is not gated (e.g. by a bootloader).
+	usbOTG.PCGCCTL.Set(0)
+
+	// Stay soft-disconnected until configuration is complete; CSRST left
+	// DCTL at its default "connected" state.
+	usbOTG.DCTL.SetBits(DCTL_SDIS)
+
+	// 5. Force device mode now that the core is out of reset. The mode
+	// change takes effect only after up to 25 ms (RM0433); poll GINTSTS.CMOD
+	// (bit 0: 0 = device) with a generous busy-wait bound.
+	usbOTG.GUSBCFG.SetBits(GUSBCFG_FDMOD)
+	for j := 0; j < 20_000_000 && usbOTG.GINTSTS.Get()&0x1 != 0; j++ {
+		arm.Asm("nop")
+	}
+
+	// Override all session/VBUS valid bits regardless of hardware pin state.
+	// GOTGCTL[2]=VBVALOEN, [3]=VBVALOVAL, [6]=BVALOEN, [7]=BVALOVAL.
+	usbOTG.GOTGCTL.SetBits(0x4 | 0x8 | 0x40 | 0x80)
+
+	// Set turnaround time: HCLK=200MHz → TRDT=6 per RM0433 Table 362.
+	usbOTG.GUSBCFG.ReplaceBits(0x6<<GUSBCFG_TRDT_Pos, 0xF<<GUSBCFG_TRDT_Pos, 0)
+
+	// 6. FIFO Configuration (total 1024 words shared by RX + all TX FIFOs).
+	// initEndpoint assigns TX FIFO n to IN endpoint n, so every IN endpoint
+	// 1..8 needs a configured FIFO even if the current class uses only a few.
+	usbOTG.GRXFSIZ.Set(rxFIFOWords)
+	usbOTG.GNPTXFSIZ.Set(txFIFOWords<<16 | rxFIFOWords)
+	for i, offset := 0, uint32(rxFIFOWords+txFIFOWords); i < 8; i++ {
+		usbOTG.DIEPTXF[i].Set(txFIFOWords<<16 | offset) // DIEPTXF[i] = FIFO i+1
+		offset += txFIFOWords
+	}
+
+	// Flush all FIFOs after (re)sizing them.
+	usbOTG.GRSTCTL.SetBits(GRSTCTL_RXFFLSH)
+	for usbOTG.GRSTCTL.Get()&GRSTCTL_RXFFLSH != 0 {
+	}
+	usbOTG.GRSTCTL.SetBits(GRSTCTL_TXFFLSH | GRSTCTL_TXFNUM_ALL)
+	for usbOTG.GRSTCTL.Get()&GRSTCTL_TXFFLSH != 0 {
+	}
+
+	// 7. Device Configuration
+	// Device Speed (FS)
+	usbOTG.DCFG.ReplaceBits(DCFG_DSPD_FS, 0x3, 0)
+
+	// 8. Per-endpoint interrupt masks
+	usbOTG.DIEPMSK.Set(DEPINT_XFERC)
+	usbOTG.DOEPMSK.Set(DEPINT_XFERC | DEPINT_SETUP)
+
+	// 9. Interrupts
+	// Clear anything pending, then unmask Reset, Enumeration Done,
+	// RX FIFO Non-Empty, Setup Done (via OEPINT).
+	usbOTG.GINTSTS.Set(0xFFFFFFFF)
+	usbOTG.GINTMSK.SetBits(GINT_USBSUSP | GINT_USBRST | GINT_ENUMDNE | GINT_RXFLVL | GINT_IEPINT | GINT_OEPINT)
+	// Global Interrupt Enable
+	usbOTG.GAHBCFG.SetBits(GAHBCFG_GINT)
+
+	// 10. Enable IRQ
+	i := interrupt.New(stm32.IRQ_OTG_FS, handleUSBIRQ)
+	i.SetPriority(0)
+	i.Enable()
+
+	dev.initcomplete = true
+
+	// Release soft-disconnect: pulls D+ high, making device visible to host.
+	usbOTG.DCTL.ClearBits(DCTL_SDIS)
+}
+
+func initEndpoint(ep, config uint32) {
+	if ep == 0 {
+		// Control endpoint
+		// IN
+		usbOTG.INEP[0].CTL.ReplaceBits(0, 0x3, DEPCTL_MPSIZ_Pos) // Max packet size 64 (00)
+		usbOTG.INEP[0].INT.Set(0xFF)                             // Clear interrupts
+		// OUT
+		usbOTG.OUTEP[0].CTL.ReplaceBits(0, 0x3, DEPCTL_MPSIZ_Pos) // Max packet size 64 (00)
+		usbOTG.OUTEP[0].INT.Set(0xFF)                             // Clear interrupts
+
+		// Unmask interrupts for EP0
+		usbOTG.DAINTMSK.SetBits(0x10001) // EP0 IN and OUT
+	} else {
+		isIn := (config & uint32(usb.EndpointIn)) != 0
+		typ := config & 0x03
+
+		if isIn {
+			// Configure IN endpoint — do NOT set EPENA; set it only when queuing a transfer.
+			ctl := uint32(DEPCTL_USBAEP)
+			ctl |= (typ << DEPCTL_EPTYP_Pos)
+			ctl |= (ep << DEPCTL_TXFNUM_Pos)
+			ctl |= (64 << DEPCTL_MPSIZ_Pos) // MPS = 64 bytes
+			ctl |= DEPCTL_SNAK              // Start NAKing until data is ready
+			usbOTG.INEP[ep].CTL.Set(ctl)
+			usbOTG.INEP[ep].INT.Set(0xFF) // Clear any stale interrupts
+			usbOTG.DAINTMSK.SetBits(1 << ep)
+		} else {
+			// Configure OUT endpoint — do NOT set EPENA here; AckUsbOutTransfer arms it.
+			ctl := uint32(DEPCTL_USBAEP)
+			ctl |= (typ << DEPCTL_EPTYP_Pos)
+			ctl |= (64 << DEPCTL_MPSIZ_Pos) // MPS = 64 bytes
+			ctl |= DEPCTL_SNAK
+			usbOTG.OUTEP[ep].CTL.Set(ctl)
+			usbOTG.OUTEP[ep].INT.Set(0xFF) // Clear any stale interrupts
+			usbOTG.DAINTMSK.SetBits(1 << (ep + 16))
+			// Arm immediately so host can send data.
+			AckUsbOutTransfer(ep)
+		}
+	}
+}
+
+func handleUSBSetAddress(setup usb.Setup) bool {
+	addr := uint32(setup.WValueL)
+	usbOTG.DCFG.ReplaceBits(addr<<4, 0x7F<<4, 0)
+	SendZlp()
+	return true
+}
+
+func SendZlp() {
+	sendUSBPacket(0, nil)
+}
+
+func sendUSBPacket(ep uint32, data []byte) {
+	// 1. Wait until the TX FIFO has room for the whole transfer, so a packet
+	// queued while the previous one is still draining cannot corrupt the FIFO.
+	// DTXFSTS reports free space in words; bounded wait in case the endpoint
+	// is stuck (e.g. host stopped polling).
+	words := uint32((len(data) + 3) / 4)
+	for i := 0; i < 1_000_000 && usbOTG.INEP[ep].TXFSTS.Get()&0xFFFF < words; i++ {
+	}
+
+	// 2. Setup transfer size
+	pktCnt := uint32((len(data) + 63) / 64)
+	if len(data) == 0 {
+		pktCnt = 1
+	}
+	usbOTG.INEP[ep].TSIZ.Set(uint32(len(data)) | (pktCnt << 19))
+
+	// 3. Enable endpoint and clear NAK
+	usbOTG.INEP[ep].CTL.SetBits(DEPCTL_EPENA | DEPCTL_CNAK)
+
+	// 4. Write data to FIFO
+	// FIFOs are at 0x1000, 0x2000, ... from base
+	fifo := (*volatile.Register32)(unsafe.Pointer(uintptr(unsafe.Pointer(usbOTG)) + 0x1000 + uintptr(ep)*0x1000))
+	for i := 0; i < len(data); i += 4 {
+		var word uint32
+		for j := 0; j < 4 && i+j < len(data); j++ {
+			word |= uint32(data[i+j]) << (8 * j)
+		}
+		fifo.Set(word)
+	}
+}
+
+func AckUsbOutTransfer(ep uint32) {
+	// Prepare for next OUT transfer
+	if ep == 0 {
+		// EP0 OUT: 1 packet, 64 bytes, 3 SETUP packets
+		usbOTG.OUTEP[0].TSIZ.Set(64 | (1 << 19) | (3 << 29))
+	} else {
+		usbOTG.OUTEP[ep].TSIZ.Set(64 | (1 << 19))
+	}
+	usbOTG.OUTEP[ep].CTL.SetBits(DEPCTL_EPENA | DEPCTL_CNAK)
+}
+
+func (dev *USBDevice) SetStallEPIn(ep uint32) {
+	usbOTG.INEP[ep].CTL.SetBits(DEPCTL_STALL)
+}
+
+func (dev *USBDevice) SetStallEPOut(ep uint32) {
+	usbOTG.OUTEP[ep].CTL.SetBits(DEPCTL_STALL)
+}
+
+func (dev *USBDevice) ClearStallEPIn(ep uint32) {
+	usbOTG.INEP[ep].CTL.ClearBits(DEPCTL_STALL)
+	usbOTG.INEP[ep].CTL.SetBits(1 << 28) // SD0PID
+}
+
+func (dev *USBDevice) ClearStallEPOut(ep uint32) {
+	usbOTG.OUTEP[ep].CTL.ClearBits(DEPCTL_STALL)
+	usbOTG.OUTEP[ep].CTL.SetBits(1 << 28) // SD0PID
+}
+
+// SendUSBInPacket sends a packet for USB (interrupt in / bulk in).
+func SendUSBInPacket(ep uint32, data []byte) bool {
+	sendUSBPacket(ep, data)
+	return true
+}
+
+// ReceiveUSBControlPacket receives a control packet (used for CDC line coding).
+//
+// This runs inside the setup handler, which itself runs inside handleUSBIRQ.
+// The interrupt cannot re-enter to deliver the data stage, so the RX FIFO is
+// drained manually here until the EP0 OUT packet arrives.
+func ReceiveUSBControlPacket() ([cdcLineInfoSize]byte, error) {
+	var b [cdcLineInfoSize]byte
+	ep0OutReceived.Set(0)
+	for i := 0; i < 1_000_000; i++ {
+		if usbOTG.GINTSTS.Get()&GINT_RXFLVL != 0 {
+			handleRxFIFO()
+		}
+		if ep0OutReceived.Get() != 0 {
+			copy(b[:], udd_ep_out_cache_buffer[0][:])
+			ep0OutReceived.Set(0)
+			return b, nil
+		}
+	}
+	return b, ErrUSBReadTimeout
+}
+
+// handleRxFIFO pops one status entry from the shared RX FIFO and processes it.
+// Called from the USB interrupt, and re-entrantly from
+// ReceiveUSBControlPacket while a setup handler is waiting for the data stage.
+func handleRxFIFO() {
+	pop := usbOTG.GRXSTSP.Get()
+	ep := pop & 0xF
+	byteCnt := (pop >> 4) & 0x7FF
+	pktSts := (pop >> 17) & 0xF
+
+	// All OUT/SETUP data is read from the shared RX FIFO (DFIFO[0]).
+	fifo := (*volatile.Register32)(unsafe.Pointer(uintptr(unsafe.Pointer(usbOTG)) + 0x1000))
+
+	switch pktSts {
+	case 0x2: // OUT data packet received
+		// Guard against out-of-range endpoint or oversized packet: both come
+		// straight from hardware and would panic if used to slice the 64-byte
+		// cache buffers. Drain and discard instead.
+		if ep >= NumberOfUSBEndpoints || byteCnt > uint32(len(udd_ep_out_cache_buffer[0])) {
+			for i := uint32(0); i < byteCnt; i += 4 {
+				fifo.Get()
+			}
+			return
+		}
+
+		buf := udd_ep_out_cache_buffer[ep][:byteCnt]
+		for i := uint32(0); i < byteCnt; i += 4 {
+			word := fifo.Get()
+			for j := uint32(0); j < 4 && i+j < byteCnt; j++ {
+				buf[i+j] = byte(word >> (8 * j))
+			}
+		}
+
+		if ep == 0 {
+			ep0OutReceived.Set(1)
+			AckUsbOutTransfer(0)
+		} else if usbRxHandler[ep] != nil {
+			if usbRxHandler[ep](buf) {
+				AckUsbOutTransfer(ep)
+			}
+		}
+
+	case 0x6: // SETUP data packet received (always 8 bytes)
+		setupBuf := udd_ep_out_cache_buffer[0][:8]
+		for i := uint32(0); i < 8; i += 4 {
+			word := fifo.Get()
+			setupBuf[i] = byte(word)
+			setupBuf[i+1] = byte(word >> 8)
+			setupBuf[i+2] = byte(word >> 16)
+			setupBuf[i+3] = byte(word >> 24)
+		}
+
+		setup := usb.NewSetup(setupBuf)
+
+		ok := false
+		if (setup.BmRequestType & 0x60) == 0 { // Standard request
+			ok = handleStandardSetup(setup)
+		} else {
+			if setup.WIndex < uint16(len(usbSetupHandler)) && usbSetupHandler[setup.WIndex] != nil {
+				ok = usbSetupHandler[setup.WIndex](setup)
+			}
+		}
+
+		if !ok {
+			// Stall EP0 — host will retry.
+			usbOTG.INEP[0].CTL.SetBits(DEPCTL_STALL)
+			usbOTG.OUTEP[0].CTL.SetBits(DEPCTL_STALL)
+		}
+		// Do NOT re-arm EP0 here. The FIFO will deliver a pktSts=4
+		// (SETUP complete) entry next; we re-arm there.
+
+	case 0x3: // OUT transfer complete (host sent ACK) — no payload.
+		// Nothing to do; EP already re-armed in case 0x2.
+
+	case 0x4: // SETUP transaction complete — re-arm EP0 for next SETUP/OUT.
+		AckUsbOutTransfer(0)
+	}
+}
+
+func handleUSBIRQ(intr interrupt.Interrupt) {
+	status := usbOTG.GINTSTS.Get()
+
+	// Suppress suspend interrupts — suspend fires before enumeration completes.
+	if status&GINT_USBSUSP != 0 {
+		usbOTG.GINTSTS.Set(GINT_USBSUSP)
+	}
+
+	if status&GINT_USBRST != 0 {
+		usbOTG.GINTSTS.Set(GINT_USBRST)
+
+		// Flush all FIFOs.
+		usbOTG.GRSTCTL.SetBits(GRSTCTL_RXFFLSH)
+		for usbOTG.GRSTCTL.Get()&GRSTCTL_RXFFLSH != 0 {
+		}
+		usbOTG.GRSTCTL.SetBits(GRSTCTL_TXFFLSH | GRSTCTL_TXFNUM_ALL)
+		for usbOTG.GRSTCTL.Get()&GRSTCTL_TXFFLSH != 0 {
+		}
+
+		// Reset device address.
+		usbOTG.DCFG.ClearBits(0x7F << 4)
+
+		// Init EP0.
+		initEndpoint(0, 0)
+		usbConfiguration = 0
+
+		// TRDT for HCLK ≥ 30 MHz → 6.
+		usbOTG.GUSBCFG.ReplaceBits(0x6<<GUSBCFG_TRDT_Pos, 0xF<<GUSBCFG_TRDT_Pos, 0)
+
+		// Arm EP0 OUT to receive first SETUP/OUT.
+		AckUsbOutTransfer(0)
+	}
+
+	if status&GINT_ENUMDNE != 0 {
+		usbOTG.GINTSTS.Set(GINT_ENUMDNE)
+		// Enumeration done: activate EP0 at negotiated speed.
+		usbOTG.INEP[0].CTL.SetBits(DEPCTL_CNAK)
+	}
+
+	if status&GINT_RXFLVL != 0 {
+		// RXFLVL is level-triggered: mask it while processing, not W1C.
+		usbOTG.GINTMSK.ClearBits(GINT_RXFLVL)
+		for usbOTG.GINTSTS.Get()&GINT_RXFLVL != 0 {
+			handleRxFIFO()
+		}
+		usbOTG.GINTMSK.SetBits(GINT_RXFLVL)
+	}
+
+	if status&GINT_IEPINT != 0 {
+		daint := usbOTG.DAINT.Get() & 0xFFFF
+		for ep := uint32(0); ep < NumberOfUSBEndpoints; ep++ {
+			if daint&(1<<ep) != 0 {
+				epInt := usbOTG.INEP[ep].INT.Get()
+				usbOTG.INEP[ep].INT.Set(epInt) // W1C
+				if epInt&DEPINT_XFERC != 0 {
+					if ep != 0 && usbTxHandler[ep] != nil {
+						usbTxHandler[ep]()
+					}
+				}
+			}
+		}
+	}
+
+	if status&GINT_OEPINT != 0 {
+		daint := (usbOTG.DAINT.Get() >> 16) & 0xFFFF
+		for ep := uint32(0); ep < NumberOfUSBEndpoints; ep++ {
+			if daint&(1<<ep) != 0 {
+				epInt := usbOTG.OUTEP[ep].INT.Get()
+				usbOTG.OUTEP[ep].INT.Set(epInt) // W1C
+			}
+		}
+	}
+}

src/machine/machine_stm32h7_wwdg.go

@@ -0,0 +1,174 @@
+//go:build stm32h7
+
+package machine
+
+import (
+	"device/stm32"
+	"unsafe"
+)
+
+// WindowWatchdog provides access to the Window Watchdog (WWDG) peripheral.
+// Unlike IWDG, WWDG must be refreshed within a specific window - not too early
+// and not too late. This provides protection against both runaway code and
+// code that gets stuck in a loop refreshing the watchdog.
+var WindowWatchdog = &windowWatchdogImpl{}
+
+// WindowWatchdogConfig holds configuration for the window watchdog timer.
+// The timeout (in microseconds) before the watchdog fires.
+// The valid range depends on System frequency.
+// At 100MHz: ~40µs to ~335ms
+type WindowWatchdogConfig struct {
+	TimeoutMicros uint32
+
+	// The window value as a percentage of timeout (0-100).
+	// Refresh must occur when counter is below this percentage of max.
+	// Default (0) sets window to 100% (no window restriction).
+	WindowPercent uint8
+}
+
+// WWDG prescaler values
+const (
+	wwdgPrescaler1   = 0 // CK Counter Clock (PCLK/4096) / 1
+	wwdgPrescaler2   = 1 // CK Counter Clock (PCLK/4096) / 2
+	wwdgPrescaler4   = 2 // CK Counter Clock (PCLK/4096) / 4
+	wwdgPrescaler8   = 3 // CK Counter Clock (PCLK/4096) / 8
+	wwdgPrescaler16  = 4 // CK Counter Clock (PCLK/4096) / 16
+	wwdgPrescaler32  = 5 // CK Counter Clock (PCLK/4096) / 32
+	wwdgPrescaler64  = 6 // CK Counter Clock (PCLK/4096) / 64
+	wwdgPrescaler128 = 7 // CK Counter Clock (PCLK/4096) / 128
+)
+
+// WWDG counter limits
+const (
+	wwdgCounterMin = 0x40 // Minimum counter value (T6 must be set)
+	wwdgCounterMax = 0x7F // Maximum counter value (7 bits)
+	wwdgWindowMax  = 0x7F // Maximum window value
+)
+
+type windowWatchdogImpl struct {
+	counter   uint8 // Configured counter reload value
+	prescaler uint8 // Configured prescaler
+}
+
+// Configure the window watchdog.
+//
+// This method should not be called after the watchdog is started.
+// The WWDG cannot be disabled once started, except by a system reset.
+//
+// Timeout formula: t_WWDG = (1/PCLK) × 4096 × 2^WDGTB × (T[5:0] + 1)
+// Where T[5:0] = counter value - 0x40
+func (wd *windowWatchdogImpl) Configure(config WindowWatchdogConfig) error {
+	// Enable WWDG clock
+	enableAltFuncClock(unsafe.Pointer(stm32.WWDG))
+
+	// Calculate prescaler and counter value from timeout
+	// Base tick = PCLK / 4096
+	// With prescaler: tick = PCLK / (4096 * 2^prescaler)
+	// Timeout = tick * (counter - 0x3F)
+
+	pclk := pclk3Freq()
+	// Base tick = PCLK / 4096
+	// Tick duration in nanoseconds = 1,000,000,000 / (pclk / 4096)
+	// Simplified: (4096 * 1,000,000,000) / pclk
+	baseTickNs := (uint64(4096) * 1000000000) / uint64(pclk)
+
+	timeoutUs := config.TimeoutMicros
+	if timeoutUs == 0 {
+		timeoutUs = 10000 // Default 10ms
+	}
+	timeoutNs := uint64(timeoutUs) * 1000
+
+	// Find the best prescaler and counter-combination
+	var bestPrescaler uint8
+	var bestCounter uint8
+	found := false
+
+	for prescaler := uint8(0); prescaler <= 7; prescaler++ {
+		// Tick duration with prescaler in nanoseconds
+		tickNs := baseTickNs << prescaler
+
+		// Counter value needed (counter - 0x3F = timeout / tick)
+		// Rearranged: counter = (timeoutNs / tickNs) + 0x3F
+		counterVal := (timeoutNs / tickNs) + 0x3F
+
+		if counterVal >= wwdgCounterMin && counterVal <= wwdgCounterMax {
+			bestPrescaler = prescaler
+			bestCounter = uint8(counterVal)
+			found = true
+			break
+		}
+	}
+
+	if !found {
+		// Use maximum timeout
+		bestPrescaler = wwdgPrescaler128
+		bestCounter = wwdgCounterMax
+	}
+
+	wd.prescaler = bestPrescaler
+	wd.counter = bestCounter
+
+	// Calculate window value
+	windowVal := uint8(wwdgWindowMax)
+	if config.WindowPercent > 0 && config.WindowPercent < 100 {
+		// Window = 0x40 + ((counter - 0x40) * percent / 100)
+		counterRange := uint16(bestCounter) - wwdgCounterMin
+		windowOffset := (counterRange * uint16(config.WindowPercent)) / 100
+		windowVal = uint8(wwdgCounterMin + windowOffset)
+	}
+	stm32.WWDG.CFR.Set((uint32(bestPrescaler) << stm32.WWDG_CFR_WDGTB_Pos) | uint32(windowVal))
+
+	return nil
+}
+
+// Start enables the window watchdog.
+// Once started, the WWDG cannot be disabled except by a system reset.
+func (wd *windowWatchdogImpl) Start() error {
+	stm32.WWDG.CR.Set(uint32(wd.counter) | (1 << 7))
+	return nil
+}
+
+// Update refreshes the window watchdog counter.
+// This must be called within the configured window to prevent a reset.
+// Calling too early (counter > window) or too late (counter <= 0x3F) causes reset.
+func (wd *windowWatchdogImpl) Update() {
+	stm32.WWDG.CR.Set(uint32(wd.counter) | (1 << 7))
+}
+
+// GetCounter returns the current WWDG counter value.
+// Useful for timing refresh operations within the window.
+func (wd *windowWatchdogImpl) GetCounter() uint8 {
+	return uint8(stm32.WWDG.CR.Get() & 0x7F)
+}
+
+// EnableEarlyWakeupInterrupt enables the Early Wakeup Interrupt (EWI).
+// The EWI is triggered when the counter reaches 0x40, giving the application
+// a chance to refresh the watchdog or perform cleanup before reset.
+func (wd *windowWatchdogImpl) EnableEarlyWakeupInterrupt() {
+	stm32.WWDG.CFR.SetBits(stm32.WWDG_CFR_EWI)
+}
+
+// ClearEarlyWakeupFlag clears the Early Wakeup Interrupt flag.
+// Must be called in the interrupt handler.
+func (wd *windowWatchdogImpl) ClearEarlyWakeupFlag() {
+	stm32.WWDG.SR.ClearBits(stm32.WWDG_SR_EWIF) // RM0433 §35.3.4: write 0 to EWIF to clear
+}
+
+// IsEarlyWakeupFlagSet returns true if the Early Wakeup Interrupt flag is set.
+func (wd *windowWatchdogImpl) IsEarlyWakeupFlagSet() bool {
+	return stm32.WWDG.SR.Get()&1 != 0
+}
+
+// GetMaxTimeout returns the maximum timeout in microseconds for the current PCLK.
+// Max timeout = (1/PCLK) × 4096 × 128 × 64
+func (wd *windowWatchdogImpl) GetMaxTimeout() uint32 {
+	pclk := uint64(pclk3Freq())
+	return uint32((uint64(4096) * 128 * 64 * 1000000) / pclk)
+}
+
+// GetMinTimeout returns the minimum timeout in microseconds for the current PCLK.
+// Min timeout = (1/PCLK) × 4096 × 1 × 1
+func (wd *windowWatchdogImpl) GetMinTimeout() uint32 {
+	pclk := uint64(pclk3Freq())
+	return uint32((uint64(4096) * 1000000) / pclk)
+}

src/machine/usb.go

@@ -1,4 +1,4 @@
-//go:build sam || nrf52840 || rp2040 || rp2350 || stm32f4 || stm32f7
+//go:build sam || nrf52840 || rp2040 || rp2350 || stm32f4 || stm32f7 || stm32h7
 
 package machine
 

src/runtime/runtime_stm32h7.go

@@ -0,0 +1,179 @@
+//go:build stm32 && stm32h7
+
+package runtime
+
+import (
+	"device/stm32"
+	"machine"
+	_ "machine/usb/cdc"
+)
+
+func init() {
+	initCLK()
+	initMPU()
+
+	machine.InitSerial()
+
+	initTickTimer(&machine.TIM3)
+}
+
+func putchar(c byte) {
+	machine.Serial.WriteByte(c)
+}
+
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+		Gosched()
+	}
+	v, _ := machine.Serial.ReadByte()
+	return v
+}
+
+func buffered() int {
+	return machine.Serial.Buffered()
+}
+
+func initCLK() {
+	// 1. Enable SYSCFG
+	stm32.RCC.APB4ENR.SetBits(stm32.RCC_APB4ENR_SYSCFGEN)
+
+	// H743/H753 have no SMPS; the NUCLEO-H753ZI runs VCORE from the internal
+	// LDO (the CR3 reset state). Supply bits in CR3 are write-once after POR,
+	// so keep LDOEN/BYPASS untouched and only enable the USB 3.3V level
+	// detector needed by the USB transceivers.
+	stm32.PWR.CR3.SetBits(stm32.PWR_CR3_USB33DEN)
+
+	// 3. Configure VOS1 (Scale 1)
+	// RM0433 §6.8.4: ACTVOSRDY must be 1 (Run mode confirmed) before changing VOS.
+	for stm32.PWR.CSR1.Get()&stm32.PWR_CSR1_ACTVOSRDY == 0 {
+	}
+	// RM0433: VOS1 is 0b11.
+	stm32.PWR.D3CR.ReplaceBits(0b11<<stm32.PWR_D3CR_VOS_Pos, stm32.PWR_D3CR_VOS_Msk, 0)
+	for stm32.PWR.D3CR.Get()&stm32.PWR_D3CR_VOSRDY == 0 {
+	}
+
+	// 4. Enable HSE
+	if machine.HSEBypass() {
+		stm32.RCC.CR.SetBits(stm32.RCC_CR_HSEBYP | stm32.RCC_CR_HSEON)
+	} else {
+		stm32.RCC.CR.SetBits(stm32.RCC_CR_HSEON)
+	}
+	for stm32.RCC.CR.Get()&stm32.RCC_CR_HSERDY == 0 {
+	}
+
+	// 5. Configure PLL1
+	pll := machine.PLLParams400MHz()
+
+	// Source: HSE (2)
+	stm32.RCC.PLLCKSELR.ReplaceBits(stm32.RCC_PLLCKSELR_PLLSRC_HSE, stm32.RCC_PLLCKSELR_PLLSRC_Msk, 0)
+	// DIVM1
+	stm32.RCC.PLLCKSELR.ReplaceBits(pll.M<<stm32.RCC_PLLCKSELR_DIVM1_Pos, stm32.RCC_PLLCKSELR_DIVM1_Msk, 0)
+
+	// PLL1CFGR: Wide VCO (0), Range based on pll.R (VCO input frequency)
+	stm32.RCC.PLLCFGR.ReplaceBits(
+		(stm32.RCC_PLLCFGR_PLL1VCOSEL_WideVCO<<stm32.RCC_PLLCFGR_PLL1VCOSEL_Pos)|
+			(pll.R<<stm32.RCC_PLLCFGR_PLL1RGE_Pos),
+		stm32.RCC_PLLCFGR_PLL1VCOSEL_Msk|stm32.RCC_PLLCFGR_PLL1RGE_Msk, 0)
+
+	// PLL1DIVR: DIVN1=pll.N, DIVP1=pll.P, DIVQ1=pll.Q
+	// PLL1P = (VCO VCO_input * N) / P
+	// PLL1Q = (VCO VCO_input * N) / Q
+	stm32.RCC.PLL1DIVR.ReplaceBits(
+		(pll.N-1)<<stm32.RCC_PLL1DIVR_DIVN1_Pos|(pll.P-1)<<stm32.RCC_PLL1DIVR_DIVP1_Pos|(pll.Q-1)<<stm32.RCC_PLL1DIVR_DIVQ1_Pos,
+		stm32.RCC_PLL1DIVR_DIVN1_Msk|stm32.RCC_PLL1DIVR_DIVP1_Msk|stm32.RCC_PLL1DIVR_DIVQ1_Msk, 0)
+
+	// Enable PLL1P (SYSCLK=400MHz) and PLL1Q (SPI1/2/3 kernel=200MHz)
+	stm32.RCC.PLLCFGR.SetBits(stm32.RCC_PLLCFGR_DIVP1EN | stm32.RCC_PLLCFGR_DIVQ1EN)
+
+	// Enable PLL1
+	stm32.RCC.CR.SetBits(stm32.RCC_CR_PLL1ON)
+	for stm32.RCC.CR.Get()&stm32.RCC_CR_PLL1RDY == 0 {
+	}
+
+	// 6. Bus Prescalers
+	// D1CPRE=1 (0), HPRE=2 (8) -> HCLK=200MHz, D1PPRE (APB3)=2 (4) -> PCLK3=100MHz
+	stm32.RCC.D1CFGR.ReplaceBits(
+		(stm32.RCC_D1CFGR_D1CPRE_Div1<<stm32.RCC_D1CFGR_D1CPRE_Pos)|
+			(stm32.RCC_D1CFGR_HPRE_Div2<<stm32.RCC_D1CFGR_HPRE_Pos)|
+			(stm32.RCC_D1CFGR_D1PPRE_Div2<<stm32.RCC_D1CFGR_D1PPRE_Pos),
+		stm32.RCC_D1CFGR_D1CPRE_Msk|stm32.RCC_D1CFGR_HPRE_Msk|stm32.RCC_D1CFGR_D1PPRE_Msk, 0)
+
+	// D2CFGR: D2PPRE1 (APB1)=2 (4) -> PCLK1=100MHz, D2PPRE2 (APB2)=2 (4) -> PCLK2=100MHz
+	stm32.RCC.D2CFGR.ReplaceBits(
+		(stm32.RCC_D2CFGR_D2PPRE1_Div2<<stm32.RCC_D2CFGR_D2PPRE1_Pos)|
+			(stm32.RCC_D2CFGR_D2PPRE2_Div2<<stm32.RCC_D2CFGR_D2PPRE2_Pos),
+		stm32.RCC_D2CFGR_D2PPRE1_Msk|stm32.RCC_D2CFGR_D2PPRE2_Msk, 0)
+
+	// D3CFGR: D3PPRE (APB4)=2 (4) -> PCLK4=100MHz
+	stm32.RCC.D3CFGR.ReplaceBits(
+		stm32.RCC_D3CFGR_D3PPRE_Div2<<stm32.RCC_D3CFGR_D3PPRE_Pos,
+		stm32.RCC_D3CFGR_D3PPRE_Msk, 0)
+
+	// 7. Flash Latency
+	// VOS1, 200MHz AXI clock -> 2 wait states, WRHIGHFREQ=2 (RM0433 Table 17).
+	stm32.FLASH.ACR.ReplaceBits(2|2<<stm32.FLASH_ACR_WRHIGHFREQ_Pos,
+		stm32.FLASH_ACR_LATENCY_Msk|stm32.FLASH_ACR_WRHIGHFREQ_Msk, 0)
+	for stm32.FLASH.ACR.Get()&stm32.FLASH_ACR_LATENCY_Msk != 2 {
+	}
+
+	// 8. Switch to PLL1
+	// SW: PLL1 (3)
+	stm32.RCC.CFGR.ReplaceBits(3<<stm32.RCC_CFGR_SW_Pos, stm32.RCC_CFGR_SW_Msk, 0)
+	for (stm32.RCC.CFGR.Get() & stm32.RCC_CFGR_SWS_Msk) != (3 << stm32.RCC_CFGR_SWS_Pos) {
+	}
+
+	// 9. Peripheral Kernel Clocks
+	// I2C1,2,3 source: HSI_KER (2) to keep 64MHz timing compatibility.
+	stm32.RCC.D2CCIP2R.ReplaceBits(stm32.RCC_D2CCIP2R_I2C123SEL_HSI_KER<<stm32.RCC_D2CCIP2R_I2C123SEL_Pos, stm32.RCC_D2CCIP2R_I2C123SEL_Msk, 0)
+	// I2C4 source: HSI_KER (2)
+	stm32.RCC.D3CCIPR.ReplaceBits(stm32.RCC_D3CCIPR_I2C4SEL_HSI_KER<<stm32.RCC_D3CCIPR_I2C4SEL_Pos, stm32.RCC_D3CCIPR_I2C4SEL_Msk, 0)
+
+	// SPI1,2,3 source: PLL1_Q (0) -> 200MHz
+	stm32.RCC.D2CCIP1R.ReplaceBits(stm32.RCC_D2CCIP1R_SPI123SEL_PLL1_Q<<stm32.RCC_D2CCIP1R_SPI123SEL_Pos, stm32.RCC_D2CCIP1R_SPI123SEL_Msk, 0)
+	// SPI4,5 source: APB (0) -> PCLK2 = 100MHz (PLL1-derived)
+	stm32.RCC.D2CCIP1R.ReplaceBits(stm32.RCC_D2CCIP1R_SPI45SEL_APB<<stm32.RCC_D2CCIP1R_SPI45SEL_Pos, stm32.RCC_D2CCIP1R_SPI45SEL_Msk, 0)
+	// SPI6 source: PCLK4 (0) -> 100MHz (PLL1-derived)
+	stm32.RCC.D3CCIPR.ReplaceBits(stm32.RCC_D3CCIPR_SPI6SEL_RCC_PCLK4<<stm32.RCC_D3CCIPR_SPI6SEL_Pos, stm32.RCC_D3CCIPR_SPI6SEL_Msk, 0)
+
+	// 10. HSI48 — used as kernel clock for RNG and USB (RM0433 §33.3 requires ≤48 MHz).
+	stm32.RCC.CR.SetBits(stm32.RCC_CR_HSI48ON)
+	for stm32.RCC.CR.Get()&stm32.RCC_CR_HSI48RDY == 0 {
+	}
+	// RNGSEL and USBSEL reset value is 0x0 (HSI48 or PLL1_Q); set explicitly to HSI48.
+	stm32.RCC.D2CCIP2R.ReplaceBits(
+		stm32.RCC_D2CCIP2R_RNGSEL_HSI48<<stm32.RCC_D2CCIP2R_RNGSEL_Pos|
+			stm32.RCC_D2CCIP2R_USBSEL_HSI48<<stm32.RCC_D2CCIP2R_USBSEL_Pos,
+		stm32.RCC_D2CCIP2R_RNGSEL_Msk|stm32.RCC_D2CCIP2R_USBSEL_Msk, 0)
+
+	// 11. Enable CRS (Clock Recovery System) for HSI48 stabilization via USB SOF.
+	stm32.RCC.APB1HENR.SetBits(stm32.RCC_APB1HENR_CRSEN)
+	stm32.CRS.CFGR.ReplaceBits(stm32.CRS_CFGR_SYNCSRC_USB_SOF<<stm32.CRS_CFGR_SYNCSRC_Pos, stm32.CRS_CFGR_SYNCSRC_Msk, 0)
+	stm32.CRS.CR.SetBits(stm32.CRS_CR_CEN | stm32.CRS_CR_AUTOTRIMEN)
+
+	// 12. Configure PLL2 for ADC (80MHz)
+	// DIVM2 = pll.M
+	stm32.RCC.PLLCKSELR.ReplaceBits(pll.M<<stm32.RCC_PLLCKSELR_DIVM2_Pos, stm32.RCC_PLLCKSELR_DIVM2_Msk, 0)
+
+	// PLL2CFGR: Wide VCO (0), Range based on pll.R (VCO input frequency)
+	stm32.RCC.PLLCFGR.ReplaceBits(
+		(stm32.RCC_PLLCFGR_PLL2VCOSEL_WideVCO<<stm32.RCC_PLLCFGR_PLL2VCOSEL_Pos)|
+			(pll.R<<stm32.RCC_PLLCFGR_PLL2RGE_Pos),
+		stm32.RCC_PLLCFGR_PLL2VCOSEL_Msk|stm32.RCC_PLLCFGR_PLL2RGE_Msk, 0)
+
+	// PLL2DIVR: DIVN2=pll.N, DIVP2=10 (Value 9)
+	// PLL2P = (VCO VCO_input * N) / 10 = 80MHz
+	stm32.RCC.PLL2DIVR.ReplaceBits(
+		(pll.N-1)<<stm32.RCC_PLL2DIVR_DIVN2_Pos|9<<stm32.RCC_PLL2DIVR_DIVP2_Pos,
+		stm32.RCC_PLL2DIVR_DIVN2_Msk|stm32.RCC_PLL2DIVR_DIVP2_Msk, 0)
+
+	// Enable DIVP2EN
+	stm32.RCC.PLLCFGR.SetBits(stm32.RCC_PLLCFGR_DIVP2EN)
+
+	// Enable PLL2
+	stm32.RCC.CR.SetBits(stm32.RCC_CR_PLL2ON)
+	for stm32.RCC.CR.Get()&stm32.RCC_CR_PLL2RDY == 0 {
+	}
+
+	// 12. ADC kernel clock source: PLL2_P (0).
+	stm32.RCC.D3CCIPR.ReplaceBits(stm32.RCC_D3CCIPR_ADCSEL_PLL2_P<<stm32.RCC_D3CCIPR_ADCSEL_Pos, stm32.RCC_D3CCIPR_ADCSEL_Msk, 0)
+}

src/runtime/runtime_stm32h7_mpu.go

@@ -0,0 +1,128 @@
+//go:build stm32 && stm32h7
+
+package runtime
+
+import (
+	"device/arm"
+	"runtime/volatile"
+	"unsafe"
+)
+
+// Cortex-M7 cache size registers (ARM TRM Table 4-2, within SCB address space).
+var (
+	scbCCSIDR = (*volatile.Register32)(unsafe.Pointer(uintptr(0xE000ED80))) // Cache Size ID Register (R)
+	scbCSELR  = (*volatile.Register32)(unsafe.Pointer(uintptr(0xE000ED84))) // Cache Size Selection Register (R/W)
+)
+
+// Cortex-M7 cache maintenance registers (ARMv7-M Architecture Ref Manual Table B3-7).
+var (
+	scbICIALLU = (*volatile.Register32)(unsafe.Pointer(uintptr(0xE000EF50))) // Invalidate all I-cache (W)
+	scbDCISW   = (*volatile.Register32)(unsafe.Pointer(uintptr(0xE000EF60))) // Invalidate D-cache by set/way (W)
+)
+
+// RASR region attribute presets for this chip's memory map (ARMv7-M
+// Architecture Ref Manual §B3.5.5). The register layout itself
+// (arm.MPU_Type, arm.MPU_RASR_* field positions) is generic to any
+// ARMv7-M core (M3/M4/M7) and lives in device/arm; only these specific
+// size/type/permission combinations are STM32H7-specific.
+const (
+	// SIZE field bits[5:1]: value = log2(region_bytes) - 1.
+	mpuRASRSize2MB   = 20 << arm.MPU_RASR_SIZE_Pos // 2MB  = 2^21, field=20
+	mpuRASRSize512KB = 18 << arm.MPU_RASR_SIZE_Pos // 512KB = 2^19, field=18
+	mpuRASRSize512MB = 28 << arm.MPU_RASR_SIZE_Pos // 512MB = 2^29, field=28
+
+	// AP field bits[26:24].
+	mpuRASRAPReadOnly   = 0x6 << arm.MPU_RASR_AP_Pos // Privileged and unprivileged read-only
+	mpuRASRAPFullAccess = 0x3 << arm.MPU_RASR_AP_Pos // Full access (privileged and unprivileged)
+
+	// Memory type encodings: TEX bits[21:19], S bit[18], C bit[17], B bit[16].
+	// Normal, Write-Through, No Write-Allocate (TEX=000, C=1, B=0, S=0).
+	mpuRASRNormalWT = arm.MPU_RASR_C
+	// Normal, Write-Back, Write-Allocate (TEX=001, C=1, B=1, S=0).
+	mpuRASRNormalWBWA = (1 << arm.MPU_RASR_TEX_Pos) | arm.MPU_RASR_C | arm.MPU_RASR_B
+	// Shared Device memory (TEX=000, C=0, B=1, S=1).
+	mpuRASRDevice = arm.MPU_RASR_S | arm.MPU_RASR_B
+)
+
+// initMPU configures the Cortex-M7 MPU, then enables L1 instruction and data
+// caches. Must be called after initCLK() and before any peripheral access.
+//
+// Memory map configured:
+//
+//	Region 0: Flash     0x08000000  2MB    Normal WT,   RO, executable
+//	Region 1: AXI SRAM  0x24000000  512KB  Normal WBWA, RW, no-execute
+//	Region 2: Peripherals 0x40000000 512MB  Shared Device, RW, no-execute
+//
+// Unmapped regions fall back to the ARMv7-M default privileged map via
+// PRIVDEFENA, keeping NVIC/SCB and other PPB accesses strongly-ordered.
+func initMPU() {
+	// Disable MPU before reconfiguring regions.
+	arm.MPU.CTRL.Set(0)
+	arm.Asm("dsb 0xF")
+	arm.Asm("isb 0xF")
+
+	// Region 0: Flash — Normal, Write-Through, read-only, executable.
+	arm.MPU.RNR.Set(0)
+	arm.MPU.RBAR.Set(0x08000000)
+	arm.MPU.RASR.Set(mpuRASRNormalWT | mpuRASRAPReadOnly | mpuRASRSize2MB | arm.MPU_RASR_ENABLE)
+
+	// Region 1: AXI SRAM — Normal, Write-Back Write-Allocate, full access, no-execute.
+	arm.MPU.RNR.Set(1)
+	arm.MPU.RBAR.Set(0x24000000)
+	arm.MPU.RASR.Set(arm.MPU_RASR_XN | mpuRASRNormalWBWA | mpuRASRAPFullAccess | mpuRASRSize512KB | arm.MPU_RASR_ENABLE)
+
+	// Region 2: Peripherals — Shared Device, full access, no-execute.
+	arm.MPU.RNR.Set(2)
+	arm.MPU.RBAR.Set(0x40000000)
+	arm.MPU.RASR.Set(arm.MPU_RASR_XN | mpuRASRDevice | mpuRASRAPFullAccess | mpuRASRSize512MB | arm.MPU_RASR_ENABLE)
+
+	// Enable MemManage fault so MPU violations raise a MemFault rather than
+	// hard-faulting directly.
+	arm.SCB.SHCSR.SetBits(arm.SCB_SHCSR_MEMFAULTENA)
+
+	// Enable MPU with privileged default background map.
+	arm.MPU.CTRL.Set(arm.MPU_CTRL_ENABLE | arm.MPU_CTRL_PRIVDEFENA)
+	arm.Asm("dsb 0xF")
+	arm.Asm("isb 0xF")
+
+	// Enable L1 caches now that the MPU defines cacheability for each region.
+	initICache()
+	initDCache()
+}
+
+// initICache invalidates then enables the L1 instruction cache.
+func initICache() {
+	arm.Asm("dsb 0xF")
+	arm.Asm("isb 0xF")
+	scbICIALLU.Set(0) // Invalidate all I-cache lines.
+	arm.Asm("dsb 0xF")
+	arm.Asm("isb 0xF")
+	arm.SCB.CCR.SetBits(arm.SCB_CCR_IC)
+	arm.Asm("dsb 0xF")
+	arm.Asm("isb 0xF")
+}
+
+// initDCache invalidates all D-cache lines by set/way then enables the cache.
+// Iterates over sets and ways read from CCSIDR so it works for any M7 cache
+// size (8–64 KB, always 4-way, 32-byte lines on STM32H743).
+func initDCache() {
+	scbCSELR.Set(0) // Select L1 D-cache.
+	arm.Asm("dsb 0xF")
+
+	ccsidr := scbCCSIDR.Get()
+	numSets := (ccsidr >> 13) & 0x7FFF // NUMSETS field (value = sets-1)
+	assoc := (ccsidr >> 3) & 0x3FF     // ASSOCIATIVITY field (value = ways-1)
+
+	// Invalidate every set/way. For a 4-way cache the way index occupies
+	// bits[31:30] of DCISW; the set index starts at bit 5 (32-byte line = 2^5).
+	for set := uint32(0); set <= numSets; set++ {
+		for way := uint32(0); way <= assoc; way++ {
+			scbDCISW.Set((way << 30) | (set << 5))
+		}
+	}
+	arm.Asm("dsb 0xF")
+
+	arm.SCB.CCR.SetBits(arm.SCB_CCR_DC)
+	arm.Asm("dsb 0xF")
+	arm.Asm("isb 0xF")
+}

targets/nucleo-h753zi.json

@@ -0,0 +1,12 @@
+{
+  "inherits": ["cortex-m7"],
+  "build-tags": ["nucleoh753zi", "stm32h753", "stm32h7", "stm32"],
+  "serial": "uart",
+  "linkerscript": "targets/stm32h7.ld",
+  "extra-files": [
+    "src/device/stm32/stm32h753.s"
+  ],
+  "flash-method": "openocd",
+  "openocd-interface": "stlink",
+  "openocd-target": "stm32h7x"
+}

targets/stm32h7.ld

@@ -0,0 +1,19 @@
+
+MEMORY
+{
+    FLASH_TEXT (rx) : ORIGIN = 0x08000000, LENGTH = 2048K
+    RAM (xrw)       : ORIGIN = 0x24000000, LENGTH = 512K
+}
+
+/*
+ * D2 SRAM (0x30000000, 288K on H753) and D3 SRAM (0x38000000, 64K) are not
+ * mapped here and unused by the runtime. If a future driver places DMA
+ * buffers there, add MPU regions for them in initMPU()
+ * (src/runtime/runtime_stm32h7_mpu.go) — they currently fall through to the
+ * default privileged WBWA map, so cache maintenance via DCacheClean/
+ * DCacheInvalidate/DCacheFlush would silently miss those addresses.
+ */
+
+_stack_size = 8K;
+
+INCLUDE "targets/arm.ld"