runtime/nrf: translate nrf sleep function from C to Go

This is the last critical part of the C runtime.

Code size is reduced by 4 bytes for examples/blinky2 (probably due to
inlining) and is unchanged for examples/test.

Makefile

@@ -36,7 +36,6 @@ CFLAGS += -I$(CURDIR)/lib/nrfx/mdk
 CFLAGS += -I$(CURDIR)/lib/CMSIS/CMSIS/Include
 CFLAGS += -DNRF52832_XXAA
 CFLAGS += -Wno-uninitialized
-RUNTIME_PARTS += build/runtime_nrf.bc
 RUNTIME_PARTS += build/nrfx_system_nrf52.bc
 OBJ += build/nrfx_startup_nrf51.o # TODO nrf52, see https://bugs.llvm.org/show_bug.cgi?id=31601
 
@@ -98,11 +97,6 @@ build/tgo: *.go
 build/%.o: src/examples/% src/examples/%/*.go build/tgo src/runtime/*.go build/runtime-$(TARGET)-combined.bc
 	./build/tgo build $(TGOFLAGS) -runtime build/runtime-$(TARGET)-combined.bc -o $@ $(subst src/,,$<)
 
-# Compile C sources for the runtime.
-build/%.bc: src/runtime/%.c src/runtime/*.h
-	@mkdir -p build
-	clang $(CFLAGS) -c -o $@ $<
-
 # Compile LLVM bitcode from LLVM source.
 build/%.bc: src/runtime/%.ll
 	$(LLAS) -o $@ $<

src/runtime/runtime_nrf.c

@@ -1,30 +0,0 @@
-
-#include "hal/nrf_gpio.h"
-#include "hal/nrf_uart.h"
-#include "nrf.h"
-#include "runtime.h"
-#include "runtime_nrf.h"
-#include <string.h>
-
-static volatile bool rtc_wakeup;
-
-void rtc_sleep(uint32_t ticks) {
-	NRF_RTC0->INTENSET = RTC_INTENSET_COMPARE0_Msk;
-	rtc_wakeup = false;
-	if (ticks == 1) {
-		// Race condition (even in hardware) at ticks == 1.
-		// TODO: fix this in a better way by detecting it, like the manual
-		// describes.
-		ticks = 2;
-	}
-	NRF_RTC0->CC[0] = (NRF_RTC0->COUNTER + ticks) & 0x00ffffff;
-	while (!rtc_wakeup) {
-		__WFI();
-	}
-}
-
-void RTC0_IRQHandler() {
-	NRF_RTC0->INTENCLR = RTC_INTENSET_COMPARE0_Msk;
-	NRF_RTC0->EVENTS_COMPARE[0] = 0;
-	rtc_wakeup = true;
-}

src/runtime/runtime_nrf.go

@@ -7,8 +7,6 @@ import (
 	"device/nrf"
 )
 
-func _Cfunc_rtc_sleep(ticks uint32)
-
 const Microsecond = 1
 
 //go:export _start
@@ -55,7 +53,7 @@ func sleep(d Duration) {
 	for ticks64 != 0 {
 		monotime()                          // update timestamp
 		ticks := uint32(ticks64) & 0x7fffff // 23 bits (to be on the safe side)
-		_Cfunc_rtc_sleep(ticks)             // TODO: not accurate (must be d / 30.5175...)
+		rtc_sleep(ticks)                    // TODO: not accurate (must be d / 30.5175...)
 		ticks64 -= Duration(ticks)
 	}
 }
@@ -88,3 +86,29 @@ func abort() {
 func align(ptr uintptr) uintptr {
 	return (ptr + 3) &^ 3
 }
+
+type __volatile bool
+
+var rtc_wakeup __volatile
+
+func rtc_sleep(ticks uint32) {
+	nrf.RTC0.INTENSET = nrf.RTC0_INTENSET_COMPARE0_Msk
+	rtc_wakeup = false
+	if ticks == 1 {
+		// Race condition (even in hardware) at ticks == 1.
+		// TODO: fix this in a better way by detecting it, like the manual
+		// describes.
+		ticks = 2
+	}
+	nrf.RTC0.CC[0] = (nrf.RTC0.COUNTER + nrf.RegValue(ticks)) & 0x00ffffff
+	for !rtc_wakeup {
+		arm.Asm("wfi")
+	}
+}
+
+//go:export RTC0_IRQHandler
+func RTC0_IRQHandler() {
+	nrf.RTC0.INTENCLR = nrf.RTC0_INTENSET_COMPARE0_Msk
+	nrf.RTC0.EVENTS_COMPARE[0] = 0
+	rtc_wakeup = true
+}