all: rewrite sleep function

time.Sleep now compiles on all systems, so lets use that.
Additionally, do a few improvements in time unit handling for the
scheduler. This should lead to somewhat longer sleep durations without
wrapping (on some platforms).

Some examples got smaller, some got bigger. In particular, code using
the scheduler got bigger and the blinky1 example got smaller (especially
on Arduino: 380 -> 314 bytes).

src/runtime/runtime_avr.go

@@ -8,13 +8,11 @@ import (
 
 const BOARD = "arduino"
 
-const Microsecond = 1
+type timeUnit uint32
 
-var currentTime uint64
+var currentTime timeUnit
 
-func init() {
-	currentTime = 0
-}
+const tickMicros = 1024 * 16384
 
 // Watchdog timer periods. These can be off by a large margin (hence the jump
 // between 64ms and 125ms which is not an exact double), so don't rely on this
@@ -53,9 +51,13 @@ func putchar(c byte) {
 //
 // TODO: not very accurate. Improve accuracy by calibrating on startup and every
 // once in a while.
-func sleep(d Duration) {
-	currentTime += uint64(d)
-	d /= 16384 // about 16ms
+//go:linkname sleep time.Sleep
+func sleep(d int64) {
+	sleepTicks(timeUnit(d / tickMicros))
+}
+
+func sleepTicks(d timeUnit) {
+	currentTime += d
 	for d != 0 {
 		sleepWDT(WDT_PERIOD_16MS)
 		d -= 1
@@ -90,7 +92,7 @@ func sleepWDT(period uint8) {
 	*avr.SMCR = 0
 }
 
-func monotime() uint64 {
+func ticks() timeUnit {
 	return currentTime
 }