to top

HAL version deprecation

In this document

In the L release of Android, we are halting support for some sensor HAL versions. The only supported versions are SENSORS_DEVICE_API_VERSION_1_0 and SENSORS_DEVICE_API_VERSION_1_3.

In the next releases, we are likely to drop support for 1_0 as well.

1_0 has no concept of batching. If possible, all devices using 1_0 SHOULD upgrade to 1_3.

1_1 and 1_2 suffer from poor definition of the batching concept, and are not supported anymore

All devices currently using 1_1 or 1_2 MUST upgrade to 1_3.

In 1_3, we simplified the notion of batching, and we introduced wake up sensors.

To upgrade to 1_3, follow the changes listed below.

Implement the batch function

Even if you do not implement batching (your hardware has no FIFO), you must implement the batch function. batch is used to set the sampling period and the maximum reporting latency for a given sensor. It replaces setDelay. setDelay will not be called anymore.

If you do not implement batching, you can implement batch by simply calling your existing setDelay function with the provided sampling_period_ns parameter.

Implement the flush function

Even if you do not implement batching, you must implement the flush function.

If you do not implement batching, flush must generate one META_DATA_FLUSH_COMPLETE event and return 0 (success).

Change your sensors_poll_device_t.common.version

your_poll_device.common.version = SENSORS_DEVICE_API_VERSION_1_3

Add the new fields to the definition of your sensors

When defining each sensor, in addition to the usual sensor_t fields:

.name =       "My magnetic field Sensor",
.vendor =     "My company",
.version
=    1,
.handle =     mag_handle,
.type =       SENSOR_TYPE_MAGNETIC_FIELD,
.maxRange =   200.0f,
.resolution = CONVERT_M,
.power =      5.0f,
.minDelay =
 16667,

you also must set the new fields, defined between 1_0 and 1_3:

.fifoReservedEventCount = 0,
.fifoMaxEventCount =   0,
.stringType =         0,
.requiredPermission = 0,
.maxDelay =      200000
.flags =
SENSOR_FLAG_CONTINUOUS_MODE,

fifoReservedEventCount: If not implementing batching, set this one to 0.

fifoMaxEventCount: If not implementing batching, set this one to 0

stringType: Set to 0 for all official android sensors (those that are defined in sensors.h), as this value will be overwritten by the framework. For non-official sensors, see sensor_t for details on how to set it.

requiredPermission: This is the permission that applications will be required to have to get access to your sensor. You can usually set this to 0 for all of your sensors, but sensors with type HEART_RATE must set this to SENSOR_PERMISSION_BODY_SENSORS.

maxDelay: This value is important and you will need to set it according to the capabilities of the sensor and of its driver.

This value is defined only for continuous and on-change sensors. It is the delay between two sensor events corresponding to the lowest frequency that this sensor supports. When lower frequencies are requested through the batch function, the events will be generated at this frequency instead. It can be used by the framework or applications to estimate when the batch FIFO may be full. If this value is not set properly, CTS will fail. For one-shot and special reporting mode sensors, set maxDelay to 0.

For continuous sensors, set it to the maximum sampling period allowed in microseconds.

The following are applicable for period_ns, maxDelay, and minDelay:

  • period_ns is in nanoseconds whereas maxDelay/minDelay are in microseconds.
  • maxDelay should always fit within a 32-bit signed integer. It is declared as 64-bit on 64-bit architectures only for binary compatibility reasons.

flags: This field defines the reporting mode of the sensor and whether the sensor is a wake up sensor.

If you do not implement batching, and are just moving from 1.0 to 1.3, set this to:

SENSOR_FLAG_WAKE_UP | SENSOR_FLAG_ONE_SHOT_MODE for one-shot sensors

SENSOR_FLAG_CONTINUOUS_MODE for continuous sensors SENSOR_FLAG_ON_CHANGE_MODE for on-change sensors except proximity SENSOR_FLAG_SPECIAL_REPORTING_MODE for sensors with special reporting mode except for the tilt detector.

SENSOR_FLAG_WAKE_UP | SENSOR_FLAG_ON_CHANGE_MODE for the proximity sensor and the Android official tilt detector sensor.

Notes when upgrading from 1_1 or 1_2

  • The batch function now nearly-always succeeds, even for sensors that do not support batching, independent of the value of the timeout argument. The only cases where the batch function might fail are internal errors, or a bad sensor_handle, or negative sampling_period_ns or negative max_report_latency_ns.
  • Whether a sensor supports batching is defined by whether it has a fifoMaxEventCount greater than 0. (In previous versions, it was based on the return value of batch().)
  • Sensors that support batching are always in what we called the “batch mode” in previous versions: even if the max_report_latency_ns parameter is 0, the sensor must still be batched, meaning the events must be stored in the FIFO when the SoC goes to suspend mode.
  • The flags parameter of the batch function is not used anymore. DRY_RUN and WAKE_UPON_FIFO_FULL are both deprecated, and will never be passed to the batch function.
  • The batch timeout argument is now referred to as the max_report_latency argument.