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//go:build nrf && nrf52840
package runtime
import (
"device/arm"
"device/nrf"
"machine"
"machine/usb/cdc"
"runtime/interrupt"
"runtime/volatile"
)
type timeUnit int64
//go:linkname systemInit SystemInit
func systemInit()
//export Reset_Handler
func main() {
if nrf.FPUPresent {
arm.SCB.CPACR.Set(0) // disable FPU if it is enabled
}
systemInit()
preinit()
run()
exit(0)
}
func init() {
cdc.EnableUSBCDC()
machine.USBDev.Configure(machine.UARTConfig{})
machine.InitSerial()
initLFCLK()
initRTC()
}
func initLFCLK() {
if machine.HasLowFrequencyCrystal {
nrf.CLOCK.LFCLKSRC.Set(nrf.CLOCK_LFCLKSTAT_SRC_Xtal)
}
nrf.CLOCK.TASKS_LFCLKSTART.Set(1)
for nrf.CLOCK.EVENTS_LFCLKSTARTED.Get() == 0 {
}
nrf.CLOCK.EVENTS_LFCLKSTARTED.Set(0)
}
func initRTC() {
nrf.RTC1.TASKS_START.Set(1)
intr := interrupt.New(nrf.IRQ_RTC1, func(intr interrupt.Interrupt) {
if nrf.RTC1.EVENTS_COMPARE[0].Get() != 0 {
nrf.RTC1.EVENTS_COMPARE[0].Set(0)
nrf.RTC1.INTENCLR.Set(nrf.RTC_INTENSET_COMPARE0)
nrf.RTC1.EVENTS_COMPARE[0].Set(0)
rtc_wakeup.Set(1)
}
if nrf.RTC1.EVENTS_OVRFLW.Get() != 0 {
nrf.RTC1.EVENTS_OVRFLW.Set(0)
rtcOverflows.Set(rtcOverflows.Get() + 1)
}
})
nrf.RTC1.INTENSET.Set(nrf.RTC_INTENSET_OVRFLW)
intr.SetPriority(0xc0) // low priority
intr.Enable()
}
func putchar(c byte) {
machine.Serial.WriteByte(c)
}
func getchar() byte {
for machine.Serial.Buffered() == 0 {
Gosched()
}
v, _ := machine.Serial.ReadByte()
return v
}
func buffered() int {
return machine.Serial.Buffered()
}
func sleepTicks(d timeUnit) {
for d != 0 {
ticks := uint32(d) & 0x7fffff // 23 bits (to be on the safe side)
rtc_sleep(ticks)
d -= timeUnit(ticks)
}
}
var rtcOverflows volatile.Register32 // number of times the RTC wrapped around
// ticksToNanoseconds converts RTC ticks (at 32768Hz) to nanoseconds.
func ticksToNanoseconds(ticks timeUnit) int64 {
// The following calculation is actually the following, but with both sides
// reduced to reduce the risk of overflow:
// ticks * 1e9 / 32768
return int64(ticks) * 1953125 / 64
}
// nanosecondsToTicks converts nanoseconds to RTC ticks (running at 32768Hz).
func nanosecondsToTicks(ns int64) timeUnit {
// The following calculation is actually the following, but with both sides
// reduced to reduce the risk of overflow:
// ns * 32768 / 1e9
return timeUnit(ns * 64 / 1953125)
}
// Monotonically increasing number of ticks since start.
func ticks() timeUnit {
// For some ways of capturing the time atomically, see this thread:
// https://www.eevblog.com/forum/microcontrollers/correct-timing-by-timer-overflow-count/msg749617/#msg749617
// Here, instead of re-reading the counter register if an overflow has been
// detected, we simply try again because that results in (slightly) smaller
// code and is perhaps easier to prove correct.
for {
mask := interrupt.Disable()
counter := uint32(nrf.RTC1.COUNTER.Get())
overflows := rtcOverflows.Get()
hasOverflow := nrf.RTC1.EVENTS_OVRFLW.Get() != 0
interrupt.Restore(mask)
if hasOverflow {
// There was an overflow. Try again.
continue
}
// The counter is 24 bits in size, so the number of overflows form the
// upper 32 bits (together 56 bits, which covers 71493 years at
// 32768kHz: I'd argue good enough for most purposes).
return timeUnit(overflows)<<24 + timeUnit(counter)
}
}
var rtc_wakeup volatile.Register8
func rtc_sleep(ticks uint32) {
nrf.RTC1.INTENSET.Set(nrf.RTC_INTENSET_COMPARE0)
rtc_wakeup.Set(0)
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.RTC1.CC[0].Set((nrf.RTC1.COUNTER.Get() + ticks) & 0x00ffffff)
for rtc_wakeup.Get() == 0 {
waitForEvents()
}
}
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