tag	16b83caa5f0bb3881e2503b17e1a1d02de3bc384
tagger	The Android Open Source Project <initial-contribution@android.com>	Mon Jul 06 15:48:49 2020 -0700
object	0664da45aa510d504918995188d41ef249b0057d

commit	0664da45aa510d504918995188d41ef249b0057d	[log] [tgz]
author	gitbuildkicker <android-build@google.com>	Sun Apr 16 00:10:59 2017 -0700
committer	gitbuildkicker <android-build@google.com>	Sun Apr 16 00:10:59 2017 -0700
tree	7319ba82918a73dd9e4ae70833e53d854171aefb
parent	9e280e72059c7b49cb1cec7ba3fe40bfe0638f7c [diff]
parent	f6e2486aae20cfcca0548270c682d6d4fb243a5c [diff]

tree: 7319ba82918a73dd9e4ae70833e53d854171aefb

README.md

Context Hub Runtime Environment (CHRE)

Build Instructions

Build targets are arranged in the form of a variant triple consisting of:

vendor_arch_variant

The vendor is the provider of the CHRE implementation (ex: google, qcom). The arch is the CPU architecture (ie: hexagonv60, x86, cm4). The variant is the target platform (ie: slpi, nanohub, linux, googletest).

Linux

CHRE is compatible with Linux as a simulator.

Linux Build/Run

The build target for x86 linux is google_x86_linux. You can build/run the simulator with the following command:

./run_sim.sh

Linux Unit Tests

You can run all unit tests with the following command. Pass arguments to this script and they are passed to the gtest framework. (example: --gtest_filter=DynamicVector.*)

./run_tests.sh

SLPI Hexagon

First, setup paths to the Hexagon Tools (v8.x.x), SDK (v3.0), and SLPI source tree, for example:

export HEXAGON_TOOLS_PREFIX=~/Qualcomm/HEXAGON_Tools/8.0
export HEXAGON_SDK_PREFIX=~/Qualcomm/Hexagon_SDK/3.0
export SLPI_PREFIX=~/Qualcomm/msm8998/slpi_proc

Then use the provided Makefiles to build:

make google_hexagonv62_slpi -j

Directory Structure

The CHRE project is organized as follows:

chre_api
- The stable API exposed to nanoapps
core
- Common code that applies to all CHRE platforms, most notably event management.
pal
- An abstraction layer that implementers must supply to access device-specific functionality (such as GPS and Wi-Fi). The PAL is a C API which allows it to be implemented using a vendor-supplied library.
platform
- Contains the system interface that all plaforms must implement, along with implementations for individual platforms. This includes the implementation of the CHRE API.
- platform/shared
  - Contains code that will apply to multiple platforms, but not necessarily all.
- platform/linux
  - This directory contains the canonical example for running CHRE on desktop machines, primarily for simulation and testing.
apps
- A small number of sample applications are provided. These are intended to guide developers of new applications and help implementers test basic functionality quickly.
- This is reference code and is not required for the CHRE to function.
util
- Contains data structures used throughout CHRE and common utility code.

Within each of these directories, you may find a tests subdirectory containing tests written against the googletest framework.

Supplied Nanoapps

This project includes a number of nanoapps that serve as both examples of how to use CHRE, debugging tools and can perform some useful function.

All nanoapps in the apps directory are placed in a namespace when built statically with this CHRE implementation. When compiled as standalone nanoapps, there is no outer namespace on their entry points. This allows testing various CHRE subsystems without requiring dynamic loading and allows these nanoapps to coexist within a CHRE binary. Refer to apps/hello_world/hello_world.cc for a minimal example.

FeatureWorld

Any of the nanoapps that end with the term World are intended to test some feature of the system. The HelloWorld nanoapp simply exercises logging functionality, TimerWorld exercises timers and WifiWorld uses wifi, for example. These nanoapps log all results via chreLog which makes them effective tools when bringing up a new CHRE implementation.

ImuCal

This nanoapp implements IMU calibration.

Porting CHRE

This codebase is intended to be ported to a variety of operating systems. If you wish to port CHRE to a new OS, refer to the platform directory. An example of the Linux port is provided under platform/linux.

There are notes regarding initialization under platform/include/chre/platform/init.h that will also be helpful.

Coding conventions

There are many well-established coding standards within Google. The official C++ style guide is used with the exception of Android naming conventions for methods and variables. This means 2 space indents, camelCase method names, an mPrefix on class members and so on. Style rules that are not specified in the Android style guide are inherited from Google.

Google C++ Style

Use of C++

This project uses C++11, but with two main caveats:

General considerations for using C++ in an embedded environment apply. This means avoiding language features that can impose runtime overhead should be avoided, due to the relative scarcity of memory and CPU resources, and power considerations. Examples include RTTI, exceptions, overuse of dynamic memory allocation, etc. Refer to existing literature on this topic including this Technical Report on C++ Performance and so on.
Support of C++ standard libraries are not generally expected to be extensive or widespread in the embedded environments where this code will run. That means that things like and should not be used, in favor of simple platform abstractions that can be implemented directly with less effort (potentially using those libraries if they are known to be available).