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Submodule cereal
deleted from
d0ceac
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# What is cereal? [![cereal tests](https://github.com/commaai/cereal/workflows/tests/badge.svg?event=push)](https://github.com/commaai/cereal/actions) [![codecov](https://codecov.io/gh/commaai/cereal/branch/master/graph/badge.svg)](https://codecov.io/gh/commaai/cereal) | ||
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cereal is both a messaging spec for robotics systems as well as generic high performance IPC pub sub messaging with a single publisher and multiple subscribers. | ||
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Imagine this use case: | ||
* A sensor process reads gyro measurements directly from an IMU and publishes a `sensorEvents` packet | ||
* A calibration process subscribes to the `sensorEvents` packet to use the IMU | ||
* A localization process subscribes to the `sensorEvents` packet to use the IMU also | ||
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## Messaging Spec | ||
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You'll find the message types in [log.capnp](log.capnp). It uses [Cap'n proto](https://capnproto.org/capnp-tool.html) and defines one struct called `Event`. | ||
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All `Events` have a `logMonoTime` and a `valid`. Then a big union defines the packet type. | ||
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### Best Practices | ||
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- **All fields must describe quantities in SI units**, unless otherwise specified in the field name. | ||
- In the context of the message they are in, field names should be completely unambiguous. | ||
- All values should be easy to plot and be human-readable with minimal parsing. | ||
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### Maintaining backwards-compatibility | ||
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When making changes to the messaging spec you want to maintain backwards-compatibility, such that old logs can | ||
be parsed with a new version of cereal. Adding structs and adding members to structs is generally safe, most other | ||
things are not. Read more details [here](https://capnproto.org/language.html). | ||
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### Custom forks | ||
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Forks of [openpilot](https://github.com/commaai/openpilot) might want to add things to the messaging | ||
spec, however this could conflict with future changes made in mainline cereal/openpilot. Rebasing against mainline openpilot | ||
then means breaking backwards-compatibility with all old logs of your fork. So we added reserved events in | ||
[custom.capnp](custom.capnp) that we will leave empty in mainline cereal/openpilot. **If you only modify those, you can ensure your | ||
fork will remain backwards-compatible with all versions of mainline cereal/openpilot and your fork.** | ||
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## Pub Sub Backends | ||
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cereal supports two backends, one based on [zmq](https://zeromq.org/) and another called [msgq](messaging/msgq.cc), a custom pub sub based on shared memory that doesn't require the bytes to pass through the kernel. | ||
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Example | ||
--- | ||
```python | ||
import cereal.messaging as messaging | ||
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# in subscriber | ||
sm = messaging.SubMaster(['sensorEvents']) | ||
while 1: | ||
sm.update() | ||
print(sm['sensorEvents']) | ||
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``` | ||
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```python | ||
# in publisher | ||
pm = messaging.PubMaster(['sensorEvents']) | ||
dat = messaging.new_message('sensorEvents', size=1) | ||
dat.sensorEvents[0] = {"gyro": {"v": [0.1, -0.1, 0.1]}} | ||
pm.send('sensorEvents', dat) | ||
``` |
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Import('env', 'envCython', 'arch', 'common', 'messaging') | ||
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import shutil | ||
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cereal_dir = Dir('.') | ||
gen_dir = Dir('gen') | ||
other_dir = Dir('#msgq/messaging') | ||
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# Build cereal | ||
schema_files = ['log.capnp', 'car.capnp', 'legacy.capnp', 'custom.capnp'] | ||
env.Command(["gen/c/include/c++.capnp.h"], [], "mkdir -p " + gen_dir.path + "/c/include && touch $TARGETS") | ||
env.Command([f'gen/cpp/{s}.c++' for s in schema_files] + [f'gen/cpp/{s}.h' for s in schema_files], | ||
schema_files, | ||
f"capnpc --src-prefix={cereal_dir.path} $SOURCES -o c++:{gen_dir.path}/cpp/") | ||
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# TODO: remove non shared cereal and messaging | ||
cereal_objects = env.SharedObject([f'gen/cpp/{s}.c++' for s in schema_files]) | ||
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cereal = env.Library('cereal', cereal_objects) | ||
env.SharedLibrary('cereal_shared', cereal_objects) | ||
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# Build messaging | ||
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services_h = env.Command(['services.h'], ['services.py'], 'python3 ' + cereal_dir.path + '/services.py > $TARGET') | ||
env.Program('messaging/bridge', ['messaging/bridge.cc'], LIBS=[messaging, 'zmq', common]) | ||
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socketmaster = env.SharedObject(['messaging/socketmaster.cc']) | ||
socketmaster = env.Library('socketmaster', socketmaster) | ||
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Export('cereal', 'socketmaster') |
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import os | ||
import capnp | ||
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CEREAL_PATH = os.path.dirname(os.path.abspath(__file__)) | ||
capnp.remove_import_hook() | ||
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log = capnp.load(os.path.join(CEREAL_PATH, "log.capnp")) | ||
car = capnp.load(os.path.join(CEREAL_PATH, "car.capnp")) | ||
custom = capnp.load(os.path.join(CEREAL_PATH, "custom.capnp")) |
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