feat: add new board blinky example, nRF52840

.gitignore

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+/**/build/

templates/blinky/nRF52840dk/Makefile

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+CFLAGS ?= -W -Wall -Wextra -Werror -Wundef -Wshadow -Wdouble-promotion -Wformat-truncation -fno-common
+CFLAGS += -g3 -Os -ffunction-sections -fdata-sections -Wno-shadow
+CFLAGS += -mcpu=cortex-m4
+SOURCES = main.c
+
+build: 
+	mkdir build
+	arm-none-eabi-gcc $(SOURCES) -c $(CFLAGS) -o ./build/main.o
+	arm-none-eabi-gcc -T link.ld -nostdlib ./build/main.o -o ./build/firmware.elf
+	arm-none-eabi-objcopy -Oihex ./build/firmware.elf ./build/firmware.hex
+
+flash: 
+	nrfjprog -f NRF52 --program ./build/firmware.hex --recover --verify
+	nrfjprog -f NRF52 --reset
+
+clean:
+	rm -rf ./build 

templates/blinky/nRF52840dk/hal.h

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+#define P0 ((struct gpio *) 0x50000000)
+#define P1 ((struct gpio *) 0x50000300)
+#define BUILD_IN_LED_1 13
+
+enum { GPIO_MODE_INPUT, GPIO_MODE_OUTPUT };
+enum { LOW, HIGH };
+
+struct gpio {
+  volatile uint32_t RESERVED[321], OUT, OUTSET, OUTCLR, IN, DIR, DIRSET, DIRCLR, LATCH, DETECTMODE, PIN_CNF[32];
+};
+
+void set_gpio_mode(struct gpio * port, int pin, int mode) {
+  port->DIR |= mode << pin;
+}
+
+void gpio_write(struct gpio * port, int pin, int value) {
+  if (value == 1)
+    port->OUTSET |= 1 << pin;
+  else
+    port->OUTCLR |= 1 << pin;
+}
+
+static inline void spin(volatile uint32_t count) {
+  while (count--) (void) 0;
+}

templates/blinky/nRF52840dk/link.ld

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+ENTRY(_reset);
+
+MEMORY {
+  flash(rx)  : ORIGIN = 0x00000000, LENGTH = 1M 
+  sram(rwx) : ORIGIN = 0x20000000, LENGTH = 256k
+}
+_estack     = ORIGIN(sram) + LENGTH(sram);
+
+SECTIONS {
+  .vectors  : { KEEP(*(.vectors)) }   > flash
+  .text     : { *(.text*) }           > flash
+  .rodata   : { *(.rodata*) }         > flash
+
+  .data : {
+    _sdata = .;   /* .data section start */
+    *(.first_data)
+    *(.data SORT(.data.*))
+    _edata = .;  /* .data section end */
+  } > sram AT > flash
+  _sidata = LOADADDR(.data);
+
+  .bss : {
+    _sbss = .;              /* .bss section start */
+    *(.bss SORT(.bss.*) COMMON)
+    _ebss = .;              /* .bss section end */
+  } > sram
+
+  . = ALIGN(8);
+  _end = .;     /* for cmsis_gcc.h  */
+}

templates/blinky/nRF52840dk/main.c

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+#include <stdint.h>
+#include "hal.h"
+
+int main(void) {
+  set_gpio_mode(P0, BUILD_IN_LED_1, GPIO_MODE_OUTPUT);
+
+  while (1) {
+    gpio_write(P0, BUILD_IN_LED_1, HIGH);
+    spin(9999999);
+    gpio_write(P0, BUILD_IN_LED_1, LOW);
+    spin(9999999);
+  }
+}
+
+// Startup code
+__attribute__((naked, noreturn)) void _reset(void) {
+  // memset .bss to zero, and copy .data section to RAM region
+  extern long _sbss, _ebss, _sdata, _edata, _sidata;
+  for (long *dst = &_sbss; dst < &_ebss; dst++) *dst = 0;
+  for (long *dst = &_sdata, *src = &_sidata; dst < &_edata;) *dst++ = *src++;
+
+  main();             // Call main()
+  for (;;) (void) 0;  // Infinite loop in the case if main() returns
+}
+
+extern void _estack(void);  // Defined in link.ld
+
+// 16 standard and 42 nRF52-specific handlers
+__attribute__((section(".vectors"))) void (*const tab[16 + 42])(void) = {
+    _estack, _reset};
+