runtime: Implement GPIO output

Now we can actually blink a LED!

src/runtime/nrfx_config.h

@@ -0,0 +1,4 @@
+
+#pragma once
+
+#define NRFX_ASSERT(expression) do { bool res = expression; (void)res; } while (0)

src/runtime/runtime_nrf.c

@@ -1,7 +1,9 @@
 
+#include "hal/nrf_gpio.h"
 #include "hal/nrf_uart.h"
 #include "nrf.h"
 #include "runtime.h"
+#include "runtime_nrf.h"
 #include <string.h>
 
 void uart_init(uint32_t pin_tx) {
@@ -46,6 +48,20 @@ void RTC0_IRQHandler() {
 	rtc_wakeup = true;
 }
 
+void gpio_cfg(uint32_t pin, gpio_mode_t mode) {
+	nrf_gpio_cfg(
+			pin,
+			mode == GPIO_INPUT ? NRF_GPIO_PIN_DIR_INPUT : NRF_GPIO_PIN_DIR_OUTPUT,
+			mode == GPIO_INPUT ? NRF_GPIO_PIN_INPUT_CONNECT : NRF_GPIO_PIN_INPUT_DISCONNECT,
+			NRF_GPIO_PIN_NOPULL,
+			NRF_GPIO_PIN_S0S1,
+			NRF_GPIO_PIN_NOSENSE);
+}
+
+void gpio_set(uint32_t pin, bool high) {
+	nrf_gpio_pin_write(pin, high);
+}
+
 void _start() {
 	main();
 }

src/runtime/runtime_nrf.h

@@ -2,9 +2,18 @@
 #pragma once
 
 #include <stdint.h>
+#include <stdbool.h>
 
 void uart_init(uint32_t pin_tx);
 void uart_send(uint8_t c);
 
 void rtc_init();
 void rtc_sleep(uint32_t ticks);
+
+typedef enum {
+	GPIO_INPUT,
+	GPIO_OUTPUT,
+} gpio_mode_t;
+
+void gpio_cfg(uint32_t pin, gpio_mode_t mode);
+void gpio_set(uint32_t pin, bool high);