82 lines
2.1 KiB
Go
82 lines
2.1 KiB
Go
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package system
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import (
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"fmt"
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"sync"
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"time"
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)
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func startEdgePolling(
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pinLabel string,
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pinReadFunc func() (int, error),
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pollInterval time.Duration,
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wantedEdge int,
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eventHandler func(offset int, t time.Duration, et string, sn uint32, lsn uint32),
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quitChan chan struct{},
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) error {
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if eventHandler == nil {
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return fmt.Errorf("an event handler is mandatory for edge polling")
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}
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if quitChan == nil {
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return fmt.Errorf("the quit channel is mandatory for edge polling")
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}
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const allEdges = "all"
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triggerEventOn := "none"
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switch wantedEdge {
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case digitalPinEventOnFallingEdge:
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triggerEventOn = DigitalPinEventFallingEdge
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case digitalPinEventOnRisingEdge:
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triggerEventOn = DigitalPinEventRisingEdge
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case digitalPinEventOnBothEdges:
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triggerEventOn = allEdges
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default:
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return fmt.Errorf("unsupported edge type %d for edge polling", wantedEdge)
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}
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wg := sync.WaitGroup{}
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wg.Add(1)
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go func() {
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var oldState int
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var readStart time.Time
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var firstLoopDone bool
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for {
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select {
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case <-quitChan:
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return
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default:
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// note: pure reading takes between 30us and 1ms on rasperry Pi1, typically 50us, with sysfs also 500us
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// can happen, so we use the time stamp before start of reading to reduce random duration offset
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readStart = time.Now()
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readValue, err := pinReadFunc()
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if err != nil {
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fmt.Printf("edge polling error occurred while reading the pin %s: %v", pinLabel, err)
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readValue = oldState // keep the value
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}
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if readValue != oldState {
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detectedEdge := DigitalPinEventRisingEdge
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if readValue < oldState {
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detectedEdge = DigitalPinEventFallingEdge
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}
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if firstLoopDone && (triggerEventOn == allEdges || triggerEventOn == detectedEdge) {
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eventHandler(0, time.Duration(readStart.UnixNano()), detectedEdge, 0, 0)
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}
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oldState = readValue
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}
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// the real poll interval is increased by the reading time, see also note above
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// negative or zero duration causes no sleep
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time.Sleep(pollInterval - time.Since(readStart))
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if !firstLoopDone {
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wg.Done()
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firstLoopDone = true
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}
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}
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}
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}()
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wg.Wait()
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return nil
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}
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