runtime: Convert device initialization to Go

src/runtime/runtime_nrf.go

@@ -6,15 +6,43 @@ package runtime
 // #include "runtime_nrf.h"
 import "C"
 
-func init() {
-	C.uart_init(6) // pin_tx = 6, for NRF52840-DK
-	C.rtc_init()
-}
+import (
+	"device/arm"
+	"device/nrf"
+)
 
 const Microsecond = 1
 
+func init() {
+	initUART()
+	initLFCLK()
+	initRTC()
+}
+
+func initUART() {
+	nrf.UART0.ENABLE        = nrf.UART0_ENABLE_ENABLE_Enabled
+	nrf.UART0.BAUDRATE      = nrf.UART0_BAUDRATE_BAUDRATE_Baud115200
+	nrf.UART0.TASKS_STARTTX = 1
+	nrf.UART0.PSELTXD       = 6 // pin 6 for NRF52840-DK
+}
+
+func initLFCLK() {
+	nrf.CLOCK.LFCLKSRC = nrf.CLOCK_LFCLKSTAT_SRC_Xtal
+	nrf.CLOCK.TASKS_LFCLKSTART = 1
+	for nrf.CLOCK.EVENTS_LFCLKSTARTED == 0 {}
+	nrf.CLOCK.EVENTS_LFCLKSTARTED = 0
+}
+
+func initRTC() {
+	nrf.RTC0.TASKS_START = 1
+	// TODO: set priority
+	arm.EnableIRQ(nrf.IRQ_RTC0)
+}
+
 func putchar(c byte) {
-	C.uart_send(C.uint8_t(c))
+	nrf.UART0.TXD = nrf.RegValue(c)
+	for nrf.UART0.EVENTS_TXDRDY == 0 {}
+	nrf.UART0.EVENTS_TXDRDY = 0
 }
 
 func Sleep(d Duration) {