CAF: Sensor data aggregator module

The sensor data aggregator module of the Common Application Framework (CAF) is responsible for aggregating sensor data in form of sensor_event and passing them further in packages. It can be used in both single-core and multi-core SoCs.

When used with multi-core SoCs, the sensor data aggregator module can reduce power consumption. One core gathers data from sensors and when there is sufficient data to analyze, the first core wakes up the other core and sends the aggregated data to that core.

Configuration

To enable the sensor data aggregator module, set the CONFIG_CAF_SENSOR_DATA_AGGREGATOR Kconfig option.

To use the module, you must complete the following steps:

1. Enable the CONFIG_CAF_SENSOR_DATA_AGGREGATOR option.

2. If you are using multi-core SoC and want to receive aggregated data on another core, on the second core enable the CONFIG_CAF_SENSOR_DATA_AGGREGATOR_EVENTS option.

3. Enable aggregator in devicetree file that describes the aggregator parameters you can use, for example app.overlay file. Each aggregator should be placed as a separate node. For example, the file content could look like this:

   agg0: agg0 {
           compatible = "caf,aggregator";
           sensor_descr = "accel_sim_xyz";
           buf_data_length = <240>;
           sample_size = <3>;
           status = "okay";
   };
   
   agg1: agg1 {
          compatible = "caf,aggregator";
          sensor_descr = "void_test_sensor";
          buf_data_length = <80>;
          sample_size = <1>;
          status = "okay";
   };
   

Two aggregators are defined here and each one is responsible to handle data of the different sensors. The aggregator is defined as a separate node in the devicetree and consists of the following parameters:

• compatible - This is DTS binding and should be set to caf,aggregator.

• sensor_descr - This parameter represents the description of the sensor and should be the same as the description in the CAF: Sensor manager module.

• buf_data_length - This parameter represents the length of the buffer in bytes. Its default value is 120. Set the value as a multiple of sensor sample size times the size of sensor_value (i*sample_size*sizeof(struct sensor_value)).

• sample_size - This parameter represents the sensor sample size and is expressed in sensor_value per sample. Its default value is 1.

• buf_count - This parameter represents the number of buffers in the aggregator. Its default value is 2.

• status - This parameter represents the node status and should be set to okay.

Implementation details

sensor data aggregator module subscribes to the following sensor manager events:

• sensor_state_event

• sensor_event

• sensor_data_aggregator_release_buffer_event.

The sensor data aggregator module gathers data from sensor_event and stores the data in an active aggregator_buffer. When the buffer is full, the sensor data aggregator module sends the buffer to sensor_data_aggregator_event structure. Then module searches for the next free aggregator_buffer and sets it as an active buffer.

After changing the sensor state and receiving sensor_state_event, the sensor data aggregator module sends the data that is gathered in the active buffer.

After receiving the sensor_data_aggregator_release_buffer_event, the sensor data aggregator module sets the aggregator_buffer to free state.

Several buffers can be reduced to one, when the sampling period is greater than the time needed to send and process sensor_data_aggregator_event. When sampling is much faster than the time needed to send and process the sensor_data_aggregator_event, the number of buffers should be increased.