A class to control GPIO pins using the sysfs interface

GPIOSysfs.dart

import 'dart:io';

const String _gpioExport    = '/sys/class/gpio/export';
const String _gpioUnexport  = '/sys/class/gpio/unexport';
const String _gpioPath      = '/sys/class/gpio/gpio%d';
const String _gpioDirection = '/sys/class/gpio/gpio%d/direction';
const String _gpioValue     = '/sys/class/gpio/gpio%d/value';
const String _gpioActiveLow = '/sys/class/gpio/gpio%d/active_low';

enum Direction { input, output, low, high }

extension Enum on Direction {
  String get value {
    switch (this) {
      case Direction.input:
        return 'in';
      case Direction.output:
        return 'out';
      case Direction.low:
        return 'low';
      case Direction.high:
        return 'high';
    }
  }
}

/// A class to control GPIO pins using the sysfs interface.
class GPIOSysfs {
  int pinNumber;
  Direction direction;

  GPIOSysfs(this.pinNumber, this.direction);

  factory GPIOSysfs.fromPin(int pinNumber, Direction direction) {
    var path = _gpioPath.replaceAll('%d', pinNumber.toString());
    if (!Directory(path).existsSync()) {
      // Export the pin
      File file = File(_gpioExport);
      RandomAccessFile raf = file.openSync(mode: FileMode.writeOnly);
      raf.writeStringSync(pinNumber.toString());
      // Wait for the pin to be exported
      var count = 0;
      while (!Directory(path).existsSync()) {
        sleep(Duration(milliseconds: 50));
        count++;
        if (count > 10) {
          throw Exception('Failed to export pin $pinNumber');
        }
      }
    }

    // Set the direction
    File file = File(_gpioDirection.replaceAll('%d', pinNumber.toString()));
    file.writeAsStringSync(direction.value);

    return GPIOSysfs(pinNumber, direction);
  }

  void exportPin() {
    File file = File(_gpioExport);
    RandomAccessFile raf = file.openSync(mode: FileMode.writeOnly);
    raf.writeStringSync(pinNumber.toString());
  }

  void unexportPin() {
    File file = File(_gpioUnexport);
    RandomAccessFile raf = file.openSync(mode: FileMode.writeOnly);
    raf.writeStringSync(pinNumber.toString());
  }

  void setValue(int value) {
    File file = File(_gpioValue.replaceAll('%d', pinNumber.toString()));
    file.writeAsStringSync(value.toString());
  }

  int getValue() {
    File file = File(_gpioValue.replaceAll('%d', pinNumber.toString()));
    return int.parse(file.readAsStringSync());
  }

  void setDirection(Direction direction) {
    File file = File(_gpioDirection.replaceAll('%d', pinNumber.toString()));
    file.writeAsStringSync(direction.value);
  }

  Direction getDirection() {
    File file = File(_gpioDirection.replaceAll('%d', pinNumber.toString()));
    return Direction.values
        .firstWhere((e) => e.value == file.readAsStringSync());
  }

  // This inverts the meaning of 0 and 1 in /sys/class/gpio/gpio*/value
  void setActiveLow(bool activeLow) {
    File file = File(_gpioActiveLow.replaceAll('%d', pinNumber.toString()));
    file.writeAsStringSync(activeLow ? '1' : '0');
  }

  void clearPin(int pin) {
    unexportPin();
  }
}