add stm32 nucleol476rg support

GNUmakefile

@@ -708,6 +708,8 @@ ifneq ($(STM32), 0)
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=nucleo-l432kc       examples/blinky1
 	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=nucleo-l476rg       examples/blinky1
+	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=nucleo-l552ze       examples/blinky1
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=nucleo-wl55jc       examples/blinky1

src/machine/board_nucleol476rg.go

@@ -0,0 +1,105 @@
+//go:build nucleol476rg
+
+// Schematic: https://www.st.com/resource/en/user_manual/um1724-stm32-nucleo64-boards-mb1136-stmicroelectronics.pdf
+// Datasheet: https://www.st.com/resource/en/datasheet/stm32l476je.pdf
+
+package machine
+
+import (
+	"device/stm32"
+	"runtime/interrupt"
+)
+
+const (
+	// Arduino Pins
+	A0 = PA0
+	A1 = PA1
+	A2 = PA4
+	A3 = PB0
+	A4 = PC1
+	A5 = PC0
+
+	D0  = PA3
+	D1  = PA2
+	D2  = PA10
+	D3  = PB3
+	D4  = PB5
+	D5  = PB4
+	D6  = PB10
+	D7  = PA8
+	D8  = PA9
+	D9  = PC7
+	D10 = PB6
+	D11 = PA7
+	D12 = PA6
+	D13 = PA5
+	D14 = PB9
+	D15 = PB8
+)
+
+// User LD2: the green LED is a user LED connected to ARDUINO® signal D13 corresponding
+// to STM32 I/O PA5 (pin 21) or PB13 (pin 34) depending on the STM32 target.
+const (
+	LED         = LED_BUILTIN
+	LED_BUILTIN = LED_GREEN
+	LED_GREEN   = PA5
+)
+
+const (
+	// This board does not have a user button, so
+	// use first GPIO pin by default
+	BUTTON = PA0
+)
+
+const (
+	// UART pins
+	// PA2 and PA3 are connected to the ST-Link Virtual Com Port (VCP)
+	UART_TX_PIN = PA2
+	UART_RX_PIN = PA3
+
+	// I2C pins
+	// With default solder bridge settings:
+	//    PB8 / Arduino D5 / CN3 Pin 8 is SCL
+	//    PB7 / Arduino D4 / CN3 Pin 7 is SDA
+	I2C0_SCL_PIN = PB8
+	I2C0_SDA_PIN = PB9
+
+	// SPI pins
+	SPI1_SCK_PIN = PA5
+	SPI1_SDI_PIN = PA6
+	SPI1_SDO_PIN = PA7
+	SPI0_SCK_PIN = SPI1_SCK_PIN
+	SPI0_SDI_PIN = SPI1_SDI_PIN
+	SPI0_SDO_PIN = SPI1_SDO_PIN
+)
+
+var (
+	// USART2 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.USART2,
+		TxAltFuncSelector: AF7_USART1_2_3,
+		RxAltFuncSelector: AF7_USART1_2_3,
+	}
+	DefaultUART = UART1
+
+	// I2C1 is documented, alias to I2C0 as well
+	I2C1 = &I2C{
+		Bus:             stm32.I2C1,
+		AltFuncSelector: AF4_I2C1_2_3,
+	}
+	I2C0 = I2C1
+
+	// SPI1 is documented, alias to SPI0 as well
+	SPI1 = &SPI{
+		Bus:             stm32.SPI1,
+		AltFuncSelector: AF5_SPI1_2,
+	}
+	SPI0 = SPI1
+)
+
+func init() {
+	UART1.Interrupt = interrupt.New(stm32.IRQ_USART2, _UART1.handleInterrupt)
+}

src/machine/machine_stm32l4x6.go

@@ -0,0 +1,25 @@
+//go:build stm32l4x6
+
+package machine
+
+// Peripheral abstraction layer for the stm32l4x6
+
+func CPUFrequency() uint32 {
+	return 80e6
+}
+
+// Internal use: configured speed of the APB1 and APB2 timers, this should be kept
+// in sync with any changes to runtime package which configures the oscillators
+// and clock frequencies
+const APB1_TIM_FREQ = 80e6 // 80MHz
+const APB2_TIM_FREQ = 80e6 // 80MHz
+
+//---------- I2C related code
+
+// Gets the value for TIMINGR register
+func (i2c *I2C) getFreqRange() uint32 {
+	// This is a 'magic' value calculated by STM32CubeMX
+	// for 80MHz PCLK1.
+	// TODO: Do calculations based on PCLK1
+	return 0x10909CEC
+}

src/runtime/runtime_stm32l4x6.go

@@ -0,0 +1,29 @@
+//go:build stm32 && stm32l4x6
+
+package runtime
+
+import (
+	"device/stm32"
+)
+
+/*
+clock settings
+
+	+-------------+-----------+
+	| LSE         | 32.768khz |
+	| SYSCLK      | 80mhz    |
+	| HCLK        | 80mhz    |
+	| APB1(PCLK1) | 80mhz    |
+	| APB2(PCLK2) | 80mhz    |
+	+-------------+-----------+
+*/
+const (
+	HSE_STARTUP_TIMEOUT = 0x0500
+	PLL_M               = 1
+	PLL_N               = 40
+	PLL_P               = RCC_PLLP_DIV7
+	PLL_Q               = RCC_PLLQ_DIV2
+	PLL_R               = RCC_PLLR_DIV2
+
+	MSIRANGE = stm32.RCC_CR_MSIRANGE_Range4M
+)

targets/nucleo-l476rg.json

@@ -0,0 +1,12 @@
+{
+    "inherits": ["cortex-m4"],
+    "build-tags": ["nucleol476rg", "stm32l476", "stm32l4x6", "stm32l4", "stm32"],
+    "serial": "uart",
+    "linkerscript": "targets/stm32l4x6.ld",
+    "extra-files": [
+      "src/device/stm32/stm32l4x6.s"
+    ],
+    "flash-method": "openocd",
+    "openocd-interface": "stlink-v2-1",
+    "openocd-target": "stm32l4x"
+  }

targets/stm32l4x6.ld

@@ -0,0 +1,11 @@
+
+MEMORY
+{
+  FLASH_TEXT (rx) : ORIGIN = 0x08000000, LENGTH = 1024K
+  RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 96K
+  RAM2 (xrw)      : ORIGIN = 0x10000000, LENGTH = 32K
+}
+
+_stack_size = 4K;
+
+INCLUDE "targets/arm.ld"