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AccelerometerService ​

Using the Pebble accelerometer

The AccelerometerService enables the Pebble accelerometer to detect taps, perform measures at a given frequency, and transmit samples in batches to save CPU time and processing.

For available code samples, see the feature-accel-discs example app.

Functions ​

struct attribute((packed)) AccelData

A single accelerometer sample for all three axes including timestamp and vibration rumble status.

int accel_service_peek(AccelData *data)

Peek at the last recorded reading.

Parameters ​
  • data: a pointer to a pre-allocated AccelData item
Returns ​

-1 if the accel is not running

int accel_service_set_sampling_rate(AccelSamplingRate rate)

Change the accelerometer sampling rate.

Parameters ​
  • rate: The sampling rate in Hz (10Hz, 25Hz, 50Hz, and 100Hz possible)

int accel_service_set_samples_per_update(uint32_t num_samples)

Change the number of samples buffered between each accelerometer data event.

Parameters ​
  • num_samples: the number of samples to buffer, between 0 and 25.

void accel_data_service_subscribe(uint32_t samples_per_update, AccelDataHandler handler)

Subscribe to the accelerometer data event service. Once subscribed, the handler gets called every time there are new accelerometer samples available.

Parameters ​
  • handler: A callback to be executed on accelerometer data events
  • samples_per_update: the number of samples to buffer, between 0 and 25.

void accel_data_service_unsubscribe(void)

Unsubscribe from the accelerometer data event service. Once unsubscribed, the previously registered handler will no longer be called.

void accel_tap_service_subscribe(AccelTapHandler handler)

Subscribe to the accelerometer tap event service. Once subscribed, the handler gets called on every tap event emitted by the accelerometer.

Parameters ​
  • handler: A callback to be executed on tap event

void accel_tap_service_unsubscribe(void)

Unsubscribe from the accelerometer tap event service. Once unsubscribed, the previously registered handler will no longer be called.

void accel_raw_data_service_subscribe(uint32_t samples_per_update, AccelRawDataHandler handler)

Subscribe to the accelerometer raw data event service. Once subscribed, the handler gets called every time there are new accelerometer samples available.

Parameters ​
  • handler: A callback to be executed on accelerometer data events
  • samples_per_update: the number of samples to buffer, between 0 and 25.

Enums ​

AccelAxisType

Enumerated values defining the three accelerometer axes.

Values ​
  • ACCEL_AXIS_X: Accelerometer's X axis. The positive direction along the X axis goes toward the right of the watch.
  • ACCEL_AXIS_Y: Accelerometer's Y axis. The positive direction along the Y axis goes toward the top of the watch.
  • ACCEL_AXIS_Z: Accelerometer's Z axis. The positive direction along the Z axis goes vertically out of the watchface.

AccelSamplingRate

Valid accelerometer sampling rates, in Hz.

Values ​
  • ACCEL_SAMPLING_10HZ: 10 HZ sampling rate
  • ACCEL_SAMPLING_25HZ: 25 HZ sampling rate [Default]
  • ACCEL_SAMPLING_50HZ: 50 HZ sampling rate
  • ACCEL_SAMPLING_100HZ: 100 HZ sampling rate

AccelAxisType

Enumerated values defining the three accelerometer axes.

Values ​
  • ACCEL_AXIS_X: Accelerometer's X axis. The positive direction along the X axis goes toward the right of the watch.
  • ACCEL_AXIS_Y: Accelerometer's Y axis. The positive direction along the Y axis goes toward the top of the watch.
  • ACCEL_AXIS_Z: Accelerometer's Z axis. The positive direction along the Z axis goes vertically out of the watchface.

AccelSamplingRate

Valid accelerometer sampling rates, in Hz.

Values ​
  • ACCEL_SAMPLING_10HZ: 10 HZ sampling rate
  • ACCEL_SAMPLING_25HZ: 25 HZ sampling rate [Default]
  • ACCEL_SAMPLING_50HZ: 50 HZ sampling rate
  • ACCEL_SAMPLING_100HZ: 100 HZ sampling rate

Typedefs ​

typedef void(* AccelDataHandler) (AccelData *data, uint32_t num_samples)

Callback type for accelerometer data events.

Parameters ​
  • data: Pointer to the collected accelerometer samples.
  • num_samples: the number of samples stored in data.

typedef void(* AccelRawDataHandler) (AccelRawData *data, uint32_t num_samples, uint64_t timestamp)

Callback type for accelerometer raw data events.

Parameters ​
  • data: Pointer to the collected accelerometer samples.
  • num_samples: the number of samples stored in data.
  • timestamp: the timestamp, in ms, of the first sample.

typedef void(* AccelTapHandler) (AccelAxisType axis, int32_t direction)

Callback type for accelerometer tap events.

Parameters ​
  • axis: the axis on which a tap was registered (x, y, or z)
  • direction: the direction (-1 or +1) of the tap

typedef void(* AccelDataHandler) (AccelData *data, uint32_t num_samples)

Callback type for accelerometer data events.

Parameters ​
  • data: Pointer to the collected accelerometer samples.
  • num_samples: the number of samples stored in data.

typedef void(* AccelRawDataHandler) (AccelRawData *data, uint32_t num_samples, uint64_t timestamp)

Callback type for accelerometer raw data events.

Parameters ​
  • data: Pointer to the collected accelerometer samples.
  • num_samples: the number of samples stored in data.
  • timestamp: the timestamp, in ms, of the first sample.

typedef void(* AccelTapHandler) (AccelAxisType axis, int32_t direction)

Callback type for accelerometer tap events.

Parameters ​
  • axis: the axis on which a tap was registered (x, y, or z)
  • direction: the direction (-1 or +1) of the tap