65 lines
1.4 KiB
Go
65 lines
1.4 KiB
Go
// Copyright 2017 The Periph Authors. All rights reserved.
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// Use of this source code is governed under the Apache License, Version 2.0
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// that can be found in the LICENSE file.
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package bcm283x
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import (
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"sync/atomic"
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"time"
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"periph.io/x/host/v3/cpu"
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)
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// ReadTime returns the time on a monotonic 1Mhz clock (1µs resolution).
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//
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// It only works if bcm283x-dma successfully loaded. Otherwise it returns 0.
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func ReadTime() time.Duration {
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if drvDMA.timerMemory == nil {
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return 0
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}
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// Use atomic package to safely access memory
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high := atomic.LoadUint32(&drvDMA.timerMemory.high)
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low := atomic.LoadUint32(&drvDMA.timerMemory.low)
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return (time.Duration(high)<<32 | time.Duration(low)) * time.Microsecond
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}
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// Nanospin spins the CPU without calling into the kernel code if possible.
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func Nanospin(t time.Duration) {
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start := ReadTime()
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if start == 0 {
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// Use the slow generic version.
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cpu.Nanospin(t)
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return
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}
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// TODO(maruel): Optimize code path for sub-1µs duration.
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for ReadTime()-start < t {
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}
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}
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//
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const (
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// 31:4 reserved
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timerM3 = 1 << 3 // M3
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timerM2 = 1 << 2 // M2
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timerM1 = 1 << 1 // M1
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timerM0 = 1 << 0 // M0
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)
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// Page 173
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type timerCtl uint32
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// timerMap represents the registers to access the 1Mhz timer.
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//
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// Page 172
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type timerMap struct {
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ctl timerCtl // CS
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low uint32 // CLO
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high uint32 // CHI
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c0 uint32 // 0
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c1 uint32 // C1
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c2 uint32 // C2
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c3 uint32 // C3
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}
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