IO Plugins

(This document is an incomplete draft)

An IO plugin is any class whose instances implement a Firmata compatible interface.

Minimum Plugin Class Requirements

The plugin must...

• Be a constructor function that defines a prototype object
• Be a subclass of EventEmitter
• Initialize instances that must...
  • asynchronously emit a "connected" event when the connection to a physical device has been made.
  • asynchronously emit a "ready" event when the handshake to the physical device is complete.
  • include a property named isReady whose initial value is false. isReady must be set to true in the same or previous execution turn as the the "ready" event is emitted.
    • The process of establishing a connection and becoming "ready" is irrelevant to this document's purposes.
  • include a readonly property named MODES whose value is a frozen object containing the following property/values: { INPUT: 0, OUTPUT: 1, ANALOG: 2, PWM: 3, SERVO: 4 }
  • include a readonly property named pins whose value is an array of pin configuration objects. The indices of the pins array must correspond to the pin address integer value, eg. on an Arduino UNO digital pin 0 is at index 0 and analog pin 0 is index 14. See mock-pins.js for a complete example.
    • each pin configuration object must contain the following properties and values:
      • supportedModes: an array of modes supported by this pin, eg.
        • [0, 1, 2] represents INPUT, OUTPUT, ANALOG. (Analog pin outs)
        • [0, 1, 4] represents INPUT, OUTPUT, SERVO. (Digital pin outs)
        • [0, 1, 3, 4] represents INPUT, OUTPUT, PWM, SERVO. (Digital PWM pin outs)
      • mode: the current mode this pin is set to.
      • value: the current value of this pin
        • INPUT mode: property updated via the read loop
        • OUTPUT mode: property updated via *Write methods
      • report: 1 if reporting, 0 if not reporting
      • analogChannel: corresponding analogPin index (127 if none), eg. analogChannel: 0 is A0 whose index is 14 in the pins array.
  • include a readonly property named analogPins whose value is an array of pin indices that correspond to the analog pin indices in the pins array.

Minimum API Requirements

pinMode(pin, mode)

• Set the mode of a specified pin to one of:

INPUT: 0,
OUTPUT: 1,
ANALOG: 2,
PWM: 3,
SERVO: 4

analogWrite(pin, value)

• Ensure pin mode is OUTPUT
• Ensure PWM capability
• Accept an 8 bit value (0-255) to write

digitalWrite(pin, value)

• Ensure pin mode is OUTPUT
• Write HIGH/LOW (single bit: 1 or 0)

analogRead(pin, handler)

• Create a data event stream, emitting an event approximately once per millisecond per pin.
• A corresponding "analog-read-${pin}" event is also emitted

digitalRead(pin, handler)

• Create a data event stream, emitting an event approximately once per millisecond per pin.
• A corresponding "digital-read-${pin}" event is also emitted

servoWrite TODO.