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//go:build esp32 || esp32c3
// +build esp32 esp32c3
package runtime
import (
"device/esp"
"machine"
"unsafe"
)
type timeUnit int64
func putchar(c byte) {
machine.Serial.WriteByte(c)
}
// Initialize .bss: zero-initialized global variables.
// The .data section has already been loaded by the ROM bootloader.
func clearbss() {
ptr := unsafe.Pointer(&_sbss)
for ptr != unsafe.Pointer(&_ebss) {
*(*uint32)(ptr) = 0
ptr = unsafe.Pointer(uintptr(ptr) + 4)
}
}
func initTimer() {
// Configure timer 0 in timer group 0, for timekeeping.
// EN: Enable the timer.
// INCREASE: Count up every tick (as opposed to counting down).
// DIVIDER: 16-bit prescaler, set to 2 for dividing the APB clock by two
// (40MHz).
esp.TIMG0.T0CONFIG.Set(esp.TIMG_T0CONFIG_T0_EN | esp.TIMG_T0CONFIG_T0_INCREASE | 2<<esp.TIMG_T0CONFIG_T0_DIVIDER_Pos)
// Set the timer counter value to 0.
esp.TIMG0.T0LOADLO.Set(0)
esp.TIMG0.T0LOADHI.Set(0)
esp.TIMG0.T0LOAD.Set(0) // value doesn't matter.
}
func ticks() timeUnit {
// First, update the LO and HI register pair by writing any value to the
// register. This allows reading the pair atomically.
esp.TIMG0.T0UPDATE.Set(0)
// Then read the two 32-bit parts of the timer.
return timeUnit(uint64(esp.TIMG0.T0LO.Get()) | uint64(esp.TIMG0.T0HI.Get())<<32)
}
func nanosecondsToTicks(ns int64) timeUnit {
// Calculate the number of ticks from the number of nanoseconds. At a 80MHz
// APB clock, that's 25 nanoseconds per tick with a timer prescaler of 2:
// 25 = 1e9 / (80MHz / 2)
return timeUnit(ns / 25)
}
func ticksToNanoseconds(ticks timeUnit) int64 {
// See nanosecondsToTicks.
return int64(ticks) * 25
}
// sleepTicks busy-waits until the given number of ticks have passed.
func sleepTicks(d timeUnit) {
sleepUntil := ticks() + d
for ticks() < sleepUntil {
// TODO: suspend the CPU to not burn power here unnecessarily.
}
}
func exit(code int) {
abort()
}
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