stm32: add nucleo-l031k6 support

Adds i2c for all L0 series

UART, Blinky (LED) and i2c tested

src/machine/board_nucleol031k6.go

@@ -0,0 +1,92 @@
+// +build nucleol031k6
+
+package machine
+
+import (
+	"device/stm32"
+	"runtime/interrupt"
+)
+
+const (
+	LED         = LED_BUILTIN
+	LED_BUILTIN = LED_GREEN
+	LED_GREEN   = PB3
+)
+
+const (
+	// Arduino Pins
+	A0 = PA0 // ADC_IN0
+	A1 = PA1 // ADC_IN1
+	A2 = PA3 // ADC_IN3
+	A3 = PA4 // ADC_IN4
+	A4 = PA5 // ADC_IN5 || I2C1_SDA
+	A5 = PA6 // ADC_IN6 || I2C1_SCL
+	A6 = PA7 // ADC_IN7
+	A7 = PA2 // ADC_IN2
+
+	D0  = PA10 // USART1_TX
+	D1  = PA9  // USART1_RX
+	D2  = PA12
+	D3  = PB0 // TIM2_CH3
+	D4  = PB7
+	D5  = PB6  // TIM16_CH1N
+	D6  = PB1  // TIM14_CH1
+	D9  = PA8  // TIM1_CH1
+	D10 = PA11 // SPI_CS || TIM1_CH4
+	D11 = PB5  // SPI1_MOSI || TIM3_CH2
+	D12 = PB4  // SPI1_MISO
+	D13 = PB3  // SPI1_SCK
+)
+
+const (
+	// UART pins
+	// PA2 and PA15 are connected to the ST-Link Virtual Com Port (VCP)
+	UART_TX_PIN = PA2
+	UART_RX_PIN = PA15
+
+	// SPI
+	SPI1_SCK_PIN = PB3
+	SPI1_SDI_PIN = PB5
+	SPI1_SDO_PIN = PB4
+	SPI0_SCK_PIN = SPI1_SCK_PIN
+	SPI0_SDI_PIN = SPI1_SDI_PIN
+	SPI0_SDO_PIN = SPI1_SDO_PIN
+
+	// I2C pins
+	// PB6 and PB7 are mapped to CN4 pin 7 and CN4 pin 8 respectively with the
+	// default solder bridge settings
+	I2C0_SCL_PIN  = PB7
+	I2C0_SDA_PIN  = PB6
+	I2C0_ALT_FUNC = 1
+)
+
+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.
+	// Both UART0 and UART1 refer to USART2.
+	UART0 = UART{
+		Buffer:            NewRingBuffer(),
+		Bus:               stm32.USART2,
+		TxAltFuncSelector: 4,
+		RxAltFuncSelector: 4,
+	}
+	UART1 = &UART0
+
+	// I2C1 is documented, alias to I2C0 as well
+	I2C1 = &I2C{
+		Bus:             stm32.I2C1,
+		AltFuncSelector: 1,
+	}
+	I2C0 = I2C1
+
+	// SPI
+	SPI0 = SPI{
+		Bus:             stm32.SPI1,
+		AltFuncSelector: 0,
+	}
+	SPI1 = &SPI0
+)
+
+func init() {
+	UART0.Interrupt = interrupt.New(stm32.IRQ_USART2, UART0.handleInterrupt)
+}