nrf: add nrf52840-mdk board

With the help of Chillance on GitHub.

.travis.yml

@@ -24,5 +24,6 @@ script:
   - tinygo build -o blinky2                                examples/blinky2
   - tinygo build -o test.nrf.elf      -target=pca10040     examples/test
   - tinygo build -o blinky1.nrf51.elf -target=microbit     examples/echo
+  - tinygo build -o test.nrf.elf      -target=nrf52840-mdk examples/blinky1
   - tinygo build -o blinky1.stm32.elf -target=bluepill     examples/blinky1
   - tinygo build -o blinky1.avr.o     -target=arduino      examples/blinky1 # TODO: avr-as/avr-gcc doesn't work

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
+	uart.setPins(UART_TX_PIN, UART_RX_PIN)
-	nrf.UART0.PSELRXD = 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.setPins(config.SCL, config.SDA)
-	i2c.Bus.PSELSDA = nrf.RegValue(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)
+}

targets/nrf52840-mdk.json

@@ -0,0 +1,25 @@
+{
+	"llvm-target": "armv7em-none-eabi",
+	"build-tags": ["nrf52840_mdk", "nrf52840", "nrf", "arm", "js", "wasm"],
+	"linker": "arm-none-eabi-gcc",
+	"pre-link-args": [
+		"-nostdlib",
+		"-nostartfiles",
+		"-mcpu=cortex-m4",
+		"-mthumb",
+		"-T", "targets/nrf52840.ld",
+		"-Wl,--gc-sections",
+		"-fno-exceptions", "-fno-unwind-tables",
+		"-ffunction-sections", "-fdata-sections",
+		"-Os",
+		"-DNRF52840_XXAA",
+		"-Ilib/CMSIS/CMSIS/Include",
+		"lib/nrfx/mdk/system_nrf52840.c",
+		"src/device/nrf/nrf52840.s"
+	],
+	"objcopy": "arm-none-eabi-objcopy",
+	"flash": "openocd -f interface/cmsis-dap.cfg -f target/nrf51.cfg -c 'program {hex} reset exit'",
+	"ocd-daemon": ["openocd", "-f", "interface/cmsis-dap.cfg", "-f", "target/nrf51.cfg"],
+	"gdb": "arm-none-eabi-gdb",
+	"gdb-initial-cmds": ["target remote :3333", "monitor halt", "load", "monitor reset", "c"]
+}

targets/nrf52840.ld

@@ -0,0 +1,10 @@
+
+MEMORY
+{
+    FLASH_TEXT (rw) : ORIGIN = 0x00000000, LENGTH = 1M
+    RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 256K
+}
+
+_stack_size = 4K;
+
+INCLUDE "targets/arm.ld"