tr606_din_sync.go

// Most of this code is taken from https://github.com/davecheney/gpio/tree/master/examples/blink
// Please visit Dave's repo to learn about what it's doing.

package main

import (
  "fmt"
  "os"
  "os/signal"
  "time"

  "github.com/davecheney/gpio"
  "github.com/davecheney/gpio/rpi"
)

const (
  PPQN    = 24  // Roland DIN sync spec is 24 pulses per quarter note.
  MAX_BPM = 240 // don't stress the tr-606 CPU
)

func runClock(pin gpio.Pin, bpm int) {
  if bpm > MAX_BPM {
    fmt.Printf("Please supply a reasonable tempo (< %d bpm)")
    os.Exit(0)
  }

  // in 4/4 time, 1 quarter note = 24 ppqn * (bpm / 60) pulses per second.
  // eg. 120bpm is 48 pulses per second.
  // try to make a square pulse by setting and sleeping for half a cycle each.
  hz := PPQN * (bpm / 60)
  cycle := time.Duration(1000000 / hz / 2) * time.Microsecond

  fmt.Printf("clock is running at %d bpm (%d hz with a %+v cycle)\n", bpm, hz, cycle)
  for {
      pin.Set()
      time.Sleep(cycle)
      pin.Clear()
      time.Sleep(cycle)
  }
}

func cleanup(pins []gpio.Pin) {
  for _, p := range pins {
    p.Clear()
    p.Close()
  }
}

func main() {
  clockPin, err := gpio.OpenPin(rpi.GPIO25, gpio.ModeOutput)
  if err != nil {
    fmt.Printf("Error opening pin! %s\n", err)
    os.Exit(1)
  }

  startStopPin, err := gpio.OpenPin(rpi.GPIO24, gpio.ModeOutput)
  if err != nil {
    fmt.Printf("Error opening pin! %s\n", err)
    os.Exit(1)
  }

  // Make sure pin is off on exit as good practice.
  c := make(chan os.Signal, 1)
  signal.Notify(c, os.Interrupt)
  go func() {
    for _ = range c {
      cleanup([]gpio.Pin{clockPin, startStopPin})
      os.Exit(0)
    }
  }()

  go func() {
    runClock(clockPin, 220) // 120 bpm
  }()

  // two seconds seems to be enough for the TR-606 clock to find the right tempo
  time.Sleep(2 * time.Second)

  // run the sequencer for 10 seconds
  fmt.Println("Sequencer is running at 120bpm")
  startStopPin.Set()
  time.Sleep(10 * time.Second)
  fmt.Println("Sequencer is stopping")

  cleanup([]gpio.Pin{clockPin, startStopPin})
}