nrf: add nrf52840-mdk board

With the help of Chillance on GitHub.

src/machine/board_nrf52840-mdk.go

@@ -0,0 +1,25 @@
+// +build nrf52840_mdk
+
+package machine
+
+const HasLowFrequencyCrystal = true
+
+// LEDs on the nrf52840-mdk (nRF52840 dev board)
+const (
+	LED       = LED_GREEN
+	LED_GREEN = 22
+	LED_RED   = 23
+	LED_BLUE  = 24
+)
+
+// UART pins
+const (
+	UART_TX_PIN = 20
+	UART_RX_PIN = 19
+)
+
+// I2C pins (unused)
+const (
+	SDA_PIN = 0xff
+	SCL_PIN = 0xff
+)

src/machine/machine_nrf.go

@@ -70,8 +70,7 @@ func (uart UART) Configure(config UARTConfig) {
 	uart.SetBaudRate(config.BaudRate)
 
 	// Set TX and RX pins from board.
-	nrf.UART0.PSELTXD = UART_TX_PIN
-	nrf.UART0.PSELRXD = UART_RX_PIN
+	uart.setPins(UART_TX_PIN, UART_RX_PIN)
 
 	nrf.UART0.ENABLE = nrf.UART_ENABLE_ENABLE_Enabled
 	nrf.UART0.TASKS_STARTTX = 1
@@ -165,8 +164,7 @@ func (i2c I2C) Configure(config I2CConfig) {
 	}
 
 	i2c.Bus.ENABLE = nrf.TWI_ENABLE_ENABLE_Enabled
-	i2c.Bus.PSELSCL = nrf.RegValue(config.SCL)
-	i2c.Bus.PSELSDA = nrf.RegValue(config.SDA)
+	i2c.setPins(config.SCL, config.SDA)
 }
 
 // WriteTo writes a slice of data bytes to a peripheral with a specific address.

src/machine/machine_nrf51.go

@@ -11,7 +11,17 @@ func (p GPIO) getPortPin() (*nrf.GPIO_Type, uint8) {
 	return nrf.GPIO, p.Pin
 }
 
+func (uart UART) setPins(tx, rx uint32) {
+	nrf.UART0.PSELTXD = nrf.RegValue(tx)
+	nrf.UART0.PSELRXD = nrf.RegValue(rx)
+}
+
 //go:export UART0_IRQHandler
 func handleUART0() {
 	UART0.handleInterrupt()
 }
+
+func (i2c I2C) setPins(scl, sda uint8) {
+	i2c.Bus.PSELSCL = nrf.RegValue(scl)
+	i2c.Bus.PSELSDA = nrf.RegValue(sda)
+}

src/machine/machine_nrf52.go

@@ -12,11 +12,21 @@ func (p GPIO) getPortPin() (*nrf.GPIO_Type, uint8) {
 	return nrf.P0, p.Pin
 }
 
+func (uart UART) setPins(tx, rx uint32) {
+	nrf.UART0.PSELTXD = nrf.RegValue(tx)
+	nrf.UART0.PSELRXD = nrf.RegValue(rx)
+}
+
 //go:export UARTE0_UART0_IRQHandler
 func handleUART0() {
 	UART0.handleInterrupt()
 }
 
+func (i2c I2C) setPins(scl, sda uint8) {
+	i2c.Bus.PSELSCL = nrf.RegValue(scl)
+	i2c.Bus.PSELSDA = nrf.RegValue(sda)
+}
+
 // InitADC initializes the registers needed for ADC.
 func InitADC() {
 	return // no specific setup on nrf52 machine.

src/machine/machine_nrf52840.go

@@ -0,0 +1,31 @@
+// +build nrf52840
+
+package machine
+
+import (
+	"device/nrf"
+)
+
+// Get peripheral and pin number for this GPIO pin.
+func (p GPIO) getPortPin() (*nrf.GPIO_Type, uint8) {
+	if p.Pin >= 32 {
+		return nrf.P1, p.Pin - 32
+	} else {
+		return nrf.P0, p.Pin
+	}
+}
+
+func (uart UART) setPins(tx, rx uint32) {
+	nrf.UART0.PSEL.TXD = nrf.RegValue(tx)
+	nrf.UART0.PSEL.RXD = nrf.RegValue(rx)
+}
+
+//go:export UARTE0_UART0_IRQHandler
+func handleUART0() {
+	UART0.handleInterrupt()
+}
+
+func (i2c I2C) setPins(scl, sda uint8) {
+	i2c.Bus.PSEL.SCL = nrf.RegValue(scl)
+	i2c.Bus.PSEL.SDA = nrf.RegValue(sda)
+}