Android’s Context Hub Runtime Environment (CHRE)
Android’s context hub enables the use of nanoapps. A single nanoapp has 3 entry points seen in chre_api/chre/nanoapp.h:
nanoappStartfunction used to notify the nanoapp that it is now active.
nanoappHandleEventfunction used to notify the nanoapp tha an event of interest took place.
nanoappEndfunction used to notify the nanoapp that it is now deactivated.
The CHRE connects to several frameworks called Platform Abstraction Layers (PAL)s. Note that currently, none of these are implemented for Zephyr, but they are scheduled to be added. These frameworks include:
Audio - a framework allowing nanoapps to get audio events. See pal/audio.h for API details.
GNSS - a framework allowing nanoapps to manage location and measurement sessions. See pal/gnss.h for API details.
Sensor - a framework allowing nanoapps to request changes to sensors configuration get data/bias events. See pal/sensor.h for API details.
System - a framework allowing nanoapps to make common system requests such as logging, clock, and some basic memory allocation/deallocation. See pal/system.h for API details.
WiFi - a framework allowing nanoapps to interact with the on board WiFi. See pal/wifi.h for API details.
WWAN - a framework allowing nanoapps to interact with the WWAN module such as getting the current capabilities and info. See pal/wwan.h for API details.
Building and expectations
To build the sample use the following west command:
# From the root of the zephyr repository west build -b native_posix samples/modules/chre
Once built and run, the sample application should:
Print a hello message
Notify that the event loop started via an
Notify that a nanoapp was started and assigned an instance/app ID of 1 via a
Print a message saying that the nanoapp’s start callback was called
Send an event of type
1and no data to the nanoapp
Notify that the event was processed
nanoappEndfunction of the nanoapp
Print a message notifying that it’s not possible to remove a system level nanoapp
Exit the event loop
Add an implementation of the pal/sensor.h and pal/system.h to Zephyr. These will be standalone modules that can be used independently of CHRE, but when
CONFIG_CHREis enabled will also provide an implementation of
Add a directory
chre/nanoappswhich will host various nanoapps to be used by the Zephyr community. These should each have their own Kconfig to enable them and set the appropriate dependencies. The first nanoapp will be a lid angle calculator which will use 2 accelerometers.
overlay.dtsof this sample application to include 2 emulated accelerometers and configure them to return scripted data.
Run this sample application and watch the nanoapp provide lid angle calculations based on 2 accelerometers provided by the sensors PAL framework.