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What is 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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Pub Sub Backends | ||
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cereal supports two backends, one based on [zmq](https://zeromq.org/), the other custom based on shared memory that doesn't require the bytes to pass through the kernel. | ||
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Example | ||
--- | ||
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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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# in publisher | ||
pm = messaging.PubMaster(['sensorEvents']) | ||
dat = messaging.new_message() | ||
dat.init('sensorEvents', 1) | ||
dat.sensorEvents[0] = {"gyro": {"v": [0.1,-0.1,0.1]}} | ||
pm.send('sensorEvents', dat) | ||
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