1# Context Hub Runtime Environment (CHRE) 2 3## Build Instructions 4 5Build targets are arranged in the form of a variant triple consisting of: 6 7``vendor_arch_variant`` 8 9The vendor is the provider of the CHRE implementation (ex: google, qcom). The 10arch is the CPU architecture (ie: hexagonv60, x86, cm4). The variant is the 11target platform (ie: slpi, nanohub, linux, googletest). 12 13A debug build can be obtained by appending ``_debug`` to the variant triple. As 14an example: 15 16``make google_hexagonv62_slpi`` 17``make google_hexagonv62_slpi_debug`` 18 19### Linux 20 21CHRE is compatible with Linux as a simulator. 22 23#### Linux Build/Run 24 25The simulator has system dependencies: 26 27- TCLAP 28 - Command-line argument parsing. 29- libsndfile 30 - WAV file parsing for audio support. 31 32These are the commands to install these dependencies for Ubuntu: 33 34 sudo apt-get install libtclap-dev 35 sudo apt-get install libsndfile1-dev 36 37The build target for x86 linux is ``google_x86_linux``. You can build/run the 38simulator with the following command: 39 40 ./run_sim.sh 41 42#### Linux Unit Tests 43 44You can run all unit tests with the following command. Pass arguments to this 45script and they are passed to the gtest framework. (example: 46``--gtest_filter=DynamicVector.*``) 47 48 ./run_tests.sh 49 50### CHRE Simulator for Android 51 52CHRE is also compatible with Android as a simulator. 53 54This is not intended to be a production implementation but is suitable for 55testing CHRE nanoapps on the applications processor where Android runs. It uses 56Android NDK APIs to interact with the system. 57 58### SLPI Hexagon 59 60First, setup paths to the Hexagon Tools (v8.x.x), SDK (v3.0), and SLPI source 61tree, for example: 62 63 export HEXAGON_TOOLS_PREFIX=~/Qualcomm/HEXAGON_Tools/8.0 64 export HEXAGON_SDK_PREFIX=~/Qualcomm/Hexagon_SDK/3.0 65 export SLPI_PREFIX=~/Qualcomm/msm8998/slpi_proc 66 67Then use the provided Makefiles to build: 68 69 make google_hexagonv62_slpi -j 70 71## Directory Structure 72 73The CHRE project is organized as follows: 74 75- ``chre_api`` 76 - The stable API exposed to nanoapps 77- ``core`` 78 - Common code that applies to all CHRE platforms, most notably event 79 management. 80- ``pal`` 81 - An abstraction layer that implementers must supply to access 82 device-specific functionality (such as GPS and Wi-Fi). The PAL is a C API 83 which allows it to be implemented using a vendor-supplied library. 84- ``platform`` 85 - Contains the system interface that all plaforms must implement, along with 86 implementations for individual platforms. This includes the implementation 87 of the CHRE API. 88 - ``platform/shared`` 89 - Contains code that will apply to multiple platforms, but not 90 necessarily all. 91 - ``platform/linux`` 92 - This directory contains the canonical example for running CHRE on 93 desktop machines, primarily for simulation and testing. 94- ``apps`` 95 - A small number of sample applications are provided. These are intended to 96 guide developers of new applications and help implementers test basic 97 functionality quickly. 98 - This is reference code and is not required for the CHRE to function. 99- ``util`` 100 - Contains data structures used throughout CHRE and common utility code. 101- ``variant/simulator`` 102 - Contains the CHRE variant for the simulator. This is a good example to 103 start from when porting to new devices. Variants are explained in more 104 detail below. 105 106Within each of these directories, you may find a ``tests`` subdirectory 107containing tests written against the googletest framework. 108 109### Platform Directory Structure 110 111The platform directory contains an interface that common code under ``core`` 112leverages to implement the runtime. All platforms are required to implement the 113interface provided in ``platform/include``. 114 115The following gives a more detailed explanation of the directory structure. 116 117- ``platform`` - The top-level directory for platform-specific code. 118 - ``include`` - The interface that platforms are required to implement. 119 - ``shared`` - Code that may be shared by more than one platform but not 120 necessarily required for all. 121 - ``slpi`` - The implementation of the common interface for the SLPI and any 122 SLPI-specific code. 123 - ``linux`` - The implementation of the common interface for the simulator 124 running on Linux and any simulator-specific code. 125 126Common CHRE code that is expected to run across all platforms is located in 127``core``. This code must have a stable way to access the platform-specific 128implementation of the common platform API. This is handled by providing a stable 129include path and changing the search path for the platform implementation. Here 130is an example directory layout: 131 132- ``platform`` 133 - ``<platform_name>`` 134 - ``include`` 135 - ``chre`` 136 - ``target_platform`` 137 138The build system will add ``platform/<platform_name>/include`` to the include 139search path allowing common code to find the implementation of the platform 140interface. Here is an example of core code including a platform-specific header 141in this way: 142 143``#include "chre/target_platform/log.h"`` 144 145When building for the linux platform, the file is included from: 146 147``platform/linux/include/chre/target_platform/log.h`` 148 149## Supplied Nanoapps 150 151This project includes a number of nanoapps that serve as both examples of how to 152use CHRE, debugging tools and can perform some useful function. 153 154All nanoapps in the ``apps`` directory are placed in a namespace when built 155statically with this CHRE implementation. When compiled as standalone nanoapps, 156there is no outer namespace on their entry points. This allows testing various 157CHRE subsystems without requiring dynamic loading and allows these nanoapps to 158coexist within a CHRE binary. Refer to ``apps/hello_world/hello_world.cc`` for 159a minimal example. 160 161### FeatureWorld 162 163Any of the nanoapps that end with the term World are intended to test some 164feature of the system. The HelloWorld nanoapp simply exercises logging 165functionality, TimerWorld exercises timers and WifiWorld uses wifi, for example. 166These nanoapps log all results via chreLog which makes them effective tools when 167bringing up a new CHRE implementation. 168 169### ImuCal 170 171This nanoapp implements IMU calibration. 172 173## Porting CHRE 174 175This codebase is intended to be ported to a variety of operating systems. If you 176wish to port CHRE to a new OS, refer to the ``platform`` directory. An example of 177the Linux port is provided under ``platform/linux``. 178 179There are notes regarding initialization under 180``platform/include/chre/platform/init.h`` that will also be helpful. 181 182### Important Considerations 183 184Platforms are required to implement support for invoking the constructors and 185destructors of global, non-POD types at load and unload time, respectively. This 186is required for both the runtime and nanoapps. 187 188## Coding conventions 189 190There are many well-established coding standards within Google. The official 191C++ style guide is used with the exception of Android naming conventions for 192methods and variables. This means 2 space indents, camelCase method names, an 193mPrefix on class members and so on. Style rules that are not specified in the 194Android style guide are inherited from Google. 195 196## CHRE Variants 197 198A CHRE variant allows injecting additional source files into the build on a 199per-device basis. This can be used to inject: 200 201* A version string 202 * Set to ``undefined`` if not specified 203* A static nanoapp list 204 * Empty if left undefined 205* Additional static nanoapp includes 206 * Vendor-specific nanoapps could be specified in the variant 207 208Export the ``CHRE_VARIANT_MK_INCLUDES`` containing the mk files that you wish to 209be included the CHRE variant build. Refer to ``run_sim.sh`` and the 210``variant/simulator`` subdirectory for an example as used by the simulator. 211 212* [Google C++ Style][1] 213 214[1]: https://google.github.io/styleguide/cppguide.html 215 216### Use of C++ 217 218This project uses C++11, but with two main caveats: 219 220 1. General considerations for using C++ in an embedded environment apply. This 221 means avoiding language features that can impose runtime overhead should 222 be avoided, due to the relative scarcity of memory and CPU resources, and 223 power considerations. Examples include RTTI, exceptions, overuse of dynamic 224 memory allocation, etc. Refer to existing literature on this topic 225 including this [Technical Report on C++ Performance][2] and so on. 226 2. Support of C++ standard libraries are not generally expected to be 227 extensive or widespread in the embedded environments where this code will 228 run. That means that things like <thread> and <mutex> should not be used, 229 in favor of simple platform abstractions that can be implemented directly 230 with less effort (potentially using those libraries if they are known to be 231 available). 232 233[2]: http://www.open-std.org/jtc1/sc22/wg21/docs/TR18015.pdf 234