84 lines
1.8 KiB
Go
84 lines
1.8 KiB
Go
// Copyright 2016 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 cpu
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import (
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"io"
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"io/ioutil"
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"os"
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"strconv"
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"strings"
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"sync"
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"time"
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"periph.io/x/periph/host/fs"
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)
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// MaxSpeed returns the processor maximum speed in Hz.
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//
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// Returns 0 if it couldn't be calculated.
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func MaxSpeed() int64 {
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if isLinux {
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return getMaxSpeedLinux()
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}
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return 0
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}
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// Nanospin spins for a short amount of time doing a busy loop.
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//
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// This function should be called with durations of 10µs or less.
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func Nanospin(d time.Duration) {
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// TODO(maruel): Use runtime.LockOSThread()?
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if isLinux {
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nanospinLinux(d)
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} else {
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nanospinTime(d)
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}
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}
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//
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var (
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mu sync.Mutex
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maxSpeed int64 = -1
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openFile = openFileOrig
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)
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func openFileOrig(path string, flag int) (io.ReadCloser, error) {
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f, err := fs.Open(path, flag)
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if err != nil {
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return nil, err
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}
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return f, nil
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}
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func getMaxSpeedLinux() int64 {
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mu.Lock()
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defer mu.Unlock()
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if maxSpeed == -1 {
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maxSpeed = 0
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if f, err := openFile("/sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq", os.O_RDONLY); err == nil {
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defer f.Close()
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if b, err := ioutil.ReadAll(f); err == nil {
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s := strings.TrimSpace(string(b))
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if i, err := strconv.ParseInt(s, 10, 64); err == nil {
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// Weirdly, the speed is listed as khz. :(
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maxSpeed = i * 1000
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}
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}
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}
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}
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return maxSpeed
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}
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func nanospinTime(d time.Duration) {
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// TODO(maruel): That's not optimal; it's actually pretty bad.
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// time.Sleep() sleeps for really too long, calling it repeatedly with
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// minimal value will give the caller a wake rate of 5KHz or so, depending on
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// the host. This makes it useless for bitbanging protocol implementations.
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for start := time.Now(); time.Since(start) < d; {
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}
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}
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