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Documentation and discussion point for IO Plugins

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IO Plugins

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(This document is a work in progress)

An IO Plugin is any class whose instances implement a Firmata compatible interface. For an in-depth case study of creating an IO plugin, read about the design and creation of the Galileo-IO Plugin here.

IO Plugins are used extensively by Johnny-Five to communicate with non-Arduino based hardware but may also be used independently if desired.

Available IO Plugins

The following platform IO Plugins are currently available:

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 "connect" 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 SERIAL_PORT_IDs whose value is a frozen object containing key/value pairs that represent a platform independent serial port identification.
    • 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. (Common analog read capable pins)
          • [0, 1, 4] represents INPUT, OUTPUT, SERVO. (Common digital I/O capable pins)
          • [0, 1, 3, 4] represents INPUT, OUTPUT, PWM, SERVO. (Common digital I/O and PWM capable pins)
        • 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.
  • If an essential IO feature is not implemented or cannot be implemented, the method must throw. For example, the Raspberry Pi does not support analog inputs, if user code calls through to an analogRead, the program must throw as an irrefutable means of indicating non-support.
  • If a non-essential IO feature is not implemented or cannot be implemented, the method must accept the expected arguments and indicate successful completion. For example, if it receives a callback, that callback must be called asynchronously.

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

Writing

Data writing operations must be executed in order of instruction.

analogWrite(pin, value)

pwmWrite(pin, value) (to supercede analogWrite)

  • Accept an 8 bit value (0-255) that is written to the specified pin.

digitalWrite(pin, value)

  • Accept a value (0 or 1) that is written to the specified pin.

i2cWrite(address, inBytes)

  • Write the array of inBytes to the specified address.

i2cWrite(address, register, inBytes)

  • Write the array of inBytes to the specified address and register.

i2cWriteReg(address, register, value)

  • Write the single value to the specified address and register.

serialWrite(portId, inBytes)

  • Write the array of inBytes to the specified portId.

servoWrite(pin, value)

  • Accept a value that is written to the specified pin. If the value is between 0 and 180, it is assumed to be a servo arm position in degrees. If the value is between 180 and 544, it is also assumed to be in degrees and is truncated to 180. If the value is greater than or equal to 544, it is assumed to be a duty cycle in microseconds.

Reading

All new data read processes must be asynchronous. The following methods must not block the execution process, by any means necessary. The following methods must not return the value of the new data read process.

analogRead(pin, handler)

  • Initiate a new data reading process for pin
  • The recommended new data reading frequency is greater than or equal to 200Hz. Read cycles may reduce to 50Hz per platform capability, but no less.
  • Invoke handler for all new data reads, with a single argument which is the present value read from the pin.
  • A corresponding analog-read-${pin} event is created and emitted for all new data reads, with a single argument which is the present value read from the pin (This can be used to invoke handler).

digitalRead(pin, handler)

  • Initiate a new data reading process for pin
  • The recommended new data reading frequency is greater than or equal to 200Hz. Read cycles may reduce to 50Hz per platform capability, but no less.
  • Invoke handler for all new data reads in which the data has changed from the previous data, with a single argument which is the present value read from the pin.
  • A corresponding digital-read-${pin} event is created and emitted for all new data reads in which the data has changed from the previous data, with a single argument which is the present value read from the pin (This can be used to invoke handler).

i2cRead(address, register, bytesToRead, handler)

  • Initiate a new data reading process for address and register, requesting the specified number of bytesToRead.
  • The recommended new data reading frequency is greater than or equal to 100Hz. Read cycles may reduce to 50Hz per platform capability, but no less.
  • Invoke handler for all new data reads, with a single argument which is an array containing the bytes read.
  • A corresponding i2c-reply-${address}-${register} event is created and emitted for all new data reads, with a single argument which is an array containing the bytes read. (This can be used to invoke handler).

i2cRead(address, bytesToRead, handler)

  • Initiate a new data reading process for address, requesting the specified number of bytesToRead.
  • The recommended new data reading frequency is greater than or equal to 100Hz. Read cycles may reduce to 50Hz per platform capability, but no less.
  • Invoke handler for all new data reads, with a single argument which is an array containing the bytes read.
  • A corresponding i2c-reply-${address} event is created and emitted for all new data reads, with a single argument which is an array containing the bytes read. (This can be used to invoke handler).

i2cReadOnce(address, register, bytesToRead, handler)

  • Initiate a new data reading process for address and register, for the specified number of bytesToRead.
  • This new data read occurs only once.
  • Invoke handler with a single argument which is an array containing the bytes read.
  • A corresponding i2c-reply-${address}-${register} "once" event is created and emitted, with a single argument which is an array containing the bytes read. (This can be used to invoke handler).

i2cReadOnce(address, bytesToRead, handler)

  • Initiate a new data reading process for address, requesting the specified number of bytesToRead.
  • This new data read occurs only once.
  • Invoke handler for all new data reads, with a single argument which is an array containing the bytes read.
  • A corresponding i2c-reply-${address} event is created and emitted, with a single argument which is an array containing the bytes read. (This can be used to invoke handler).

pingRead(settings, handler)

This method is defined solely to handle the needs of HCSR04 (and similar) components.

  • No pin mode specified

  • Create a single data event, invoking handler.

  • settings is an object that includes the following properties and corresponding values:

    Property Description Default Required
    pin The pin number/name attached to the servo Yes
    value HIGH or LOW HIGH No
    pulseOut Time µs for pulseIn timeout ✭ 5 No

  • handler is called with a duration value, in microseconds, which is the result of take a pulsed measurement as required by HCSR04 (and similar) devices.

serialRead(portId, handler)

serialRead(portId[, maxBytesToRead], handler)

  • Initiate a new data reading process for portId, optionally capping the read to the specified maxBytesToRead.
  • The recommended new data reading frequency is greater than or equal to 100Hz. Read cycles may reduce to 50Hz per platform capability, but no less.
  • Invoke handler for all new data reads, with a single argument which is an array containing the bytes read.
  • A corresponding serial-data-${portId} event is created and emitted for all new data reads, with a single argument which is an array containing the bytes read. (This can be used to invoke handler).

Configuring

i2cConfig(options)

  • options is an object that MUST include, at very least, the following properties and corresponding values:

    Property Description
    address The address of the I2C component

  • options may include any of the common configuration properties:

    Property Description
    bus The I2C bus
    port The I2C bus port
    delay Time µs between setting a register and reading the bus

  • i2cConfig will always be called once by every I2C component controller class in Johnny-Five. This means that any setup necessary for a given platform's I2C peripheral capabilities should be done here.

    • Examples:
      • Firmata.js will negotiate a default register read in µs and a default value for the stopTX flag.
      • Tessel-IO will negotiate the bus to use.

  • All options specified by a user program in the instantiation of a component will be forwarded to i2cConfig.

serialConfig(options)

  • Must be called to configure a serial/uart port

  • options is an object that MUST include, at very least, the following properties and corresponding values:

    Property Description
    portId Some value that identifies the serial/uart port to configure

  • options may include any of the common configuration properties:

    Property Description
    baud The baud rate
    rxPin The RX pin
    txPin The TX pin

All options specified by a user program in the instantiation of a component will be forwarded to serialConfig.

servoConfig(options)

  • May be called as an alternative to calling pinMode(pin, SERVO).

  • options is an object that MUST include, at very least, the following properties and corresponding values:

    Property Description Default Required
    pin The pin number/name attached to the servo Yes
    min The minimum PWM pulse time in microseconds ✭, ✭✭ Yes
    max The maximum PWM pulse time in microseconds ✭, ✭✭✭ Yes

  • ✭ This is platform dependent and should be tested thoroughly with as many different servos as possible.

  • ✭✭ Approximiately between 400 and 600

  • ✭✭✭ Approximately between 2200 and 2400

servoConfig(pin, min, max)

  • See #servoConfig(options)
  • This alternate MUST be supported

IO Control

These additions are still pending.

serialStop(portId)

  • Stop continuous reading of the specified serial portId.
  • This does not close the port, it stops reading it but keeps the port open.

serialClose(portId)

  • Close the specified serial portId.

serialFlush(portId)

  • Flush the specified serial portId. For hardware serial, this waits for the transmission of outgoing serial data to complete. For software serial, this removes any buffered incoming serial data.

Special Method Definitions

normalize(pin)

  • Define a special method that Johnny-Five will call when normalizing the pin value.
// Examples: 
var io = new IOPlugin();

// The board might want to map "A*" pins to their integer value, 
// eg. Arduino allows user code to write "A0" for pin 14:
io.normalize("A0"); // 14

Special Property Definitions

defaultLed

  • This is the pin address for the board's default, built-in led.

TODO

  • Define pluggable transports, for example: replacing node-serialport with socket.io-serialport and similar.

About

Documentation and discussion point for IO Plugins