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Class Notifier - Notification Stream

A Notifier contains a stream which provides notifications about state changes on any of GPIOs 0 through 31 concurrently. Each notification read from the stream contains information about the logic levels of the GPIOs and the time of the state changes accurate to a few microseconds. It's possible to handle in excess of 100000 notifications per second.

Methods

Constants

Methods

Notifier([options])

  • options - object (optional)

Returns a new Notifier object that contains a stream which provides notifications about state changes on any of GPIOs 0 through 31 concurrently. Each notification read from the stream contains information about the logic levels of the GPIOs and the time of the state changes accurate to a few microseconds. The optional options object can be used to configure which GPIOs notifications should be provided for.

The following options are supported:

  • bits - a bit mask indicating the GPIOs of interest, bit0 corresponds to GPIO0, bit1 corresponds to GPIO1, ..., bit31 corresponds to GPIO31. If a bit is set, the corresponding GPIO will be monitored for state changes. (optional, no default)

If bits are specified, notifications will be started. If no bits are specified, the start method can be used to start notifications at a later point in time.

Each notification in the stream occupies 12 bytes and has the following structure:

  • seqno - UInt16, little-endian
    • seqno starts at 0 and increments by one for each notification. It wraps around after 2^16 notifications.
  • flags - UInt16, little-endian
    • One flag is defined. If bit 6 is set (PI_NTFY_FLAGS_ALIVE) this indicates a keep alive signal on the stream and is sent once a minute in the absence of other notification activity.
  • tick - UInt32, little-endian
    • The number of microseconds since system boot. It wraps around after 1h12m. See Event: 'alert' for further information about unsigned 32 bit arithmetic in JavaScript.
  • level - UInt32, little-endian
    • Indicates the level of each GPIO. If bit x is set then GPIOx is high.

start(bits)

  • bits - a bit mask indicating the GPIOs of interest, bit0 corresponds to GPIO0, bit1 corresponds to GPIO1, ..., bit31 corresponds to GPIO31. If a bit is set, the corresponding GPIO will be monitored for state changes.

Starts notifications for the GPIOs specified in the bit mask. Returns this.

stop()

Stops notifications. Notifications can be restarted with the start method. Returns this.

close()

Stops notifications and releases resources. Returns undefined.

stream()

Returns the notification stream which is a Readable stream.

Constants

NOTIFICATION_LENGTH

The number of bytes occupied by a notification in the notification stream.

PI_NTFY_FLAGS_ALIVE

Indicates a keep alive signal on the stream and is sent once a minute in the absence of other notification activity.