PKGBUILD/vendor/periph.io/x/periph/host/bcm283x/timer.go

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2018-12-04 18:11:50 +00:00
// Copyright 2017 The Periph Authors. All rights reserved.
// Use of this source code is governed under the Apache License, Version 2.0
// that can be found in the LICENSE file.
package bcm283x
import (
"time"
"periph.io/x/periph/host/cpu"
)
// ReadTime returns the time on a monotonic 1Mhz clock (1µs resolution).
//
// It only works if bcm283x-dma successfully loaded. Otherwise it returns 0.
func ReadTime() time.Duration {
if drvDMA.timerMemory == nil {
return 0
}
return (time.Duration(drvDMA.timerMemory.high)<<32 | time.Duration(drvDMA.timerMemory.low)) * time.Microsecond
}
// Nanospin spins the CPU without calling into the kernel code if possible.
func Nanospin(t time.Duration) {
start := ReadTime()
if start == 0 {
// Use the slow generic version.
cpu.Nanospin(t)
return
}
// TODO(maruel): Optimize code path for sub-1µs duration.
for ReadTime()-start < t {
}
}
//
const (
// 31:4 reserved
timerM3 = 1 << 3 // M3
timerM2 = 1 << 2 // M2
timerM1 = 1 << 1 // M1
timerM0 = 1 << 0 // M0
)
// Page 173
type timerCtl uint32
// timerMap represents the registers to access the 1Mhz timer.
//
// Page 172
type timerMap struct {
ctl timerCtl // CS
low uint32 // CLO
high uint32 // CHI
c0 uint32 // 0
c1 uint32 // C1
c2 uint32 // C2
c3 uint32 // C3
}