IQ.Pilot Release Commit @ b6534c0

iqpilot/cereal/README.md

@@ -0,0 +1,95 @@
+# What is cereal?
+
+cereal is the messaging system for openpilot. It uses [msgq](https://github.com/commaai/msgq) as a pub/sub backend, and [Cap'n proto](https://capnproto.org/capnp-tool.html) for serialization of the structs.
+
+
+## Messaging Spec
+
+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`.
+
+All `Events` have a `logMonoTime` and a `valid`. Then a big union defines the packet type.
+
+### Best Practices
+
+- **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.
+
+### Maintaining backwards-compatibility
+
+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).
+
+### Custom forks
+
+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 openpilot and your fork.**
+
+An example of compatible changes:
+```diff
+diff --git a/cereal/custom.capnp b/cereal/custom.capnp
+index 3348e859e..3365c7b98 100644
+--- a/cereal/custom.capnp
++++ b/cereal/custom.capnp
+@@ -10,7 +10,11 @@ $Cxx.namespace("cereal");
+ # DO rename the structs
+ # DON'T change the identifier (e.g. @0x81c2f05a394cf4af)
+
+-struct CustomReserved0 @0x81c2f05a394cf4af {
++struct SteeringInfo @0x81c2f05a394cf4af {
++  active @0 :Bool;
++  steeringAngleDeg @1 :Float32;
++  steeringRateDeg @2 :Float32;
++  steeringAccelDeg @3 :Float32;
+ }
+
+ struct CustomReserved1 @0xaedffd8f31e7b55d {
+diff --git a/cereal/log.capnp b/cereal/log.capnp
+index 1209f3fd9..b189f58b6 100644
+--- a/cereal/log.capnp
++++ b/cereal/log.capnp
+@@ -2558,14 +2558,14 @@ struct Event {
+
+     # DO change the name of the field
+     # DON'T change anything after the "@"
+-    customReservedRawData0 @124 :Data;
++    rawCanData @124 :Data;
+     customReservedRawData1 @125 :Data;
+     customReservedRawData2 @126 :Data;
+
+     # DO change the name of the field and struct
+     # DON'T change the ID (e.g. @107)
+     # DON'T change which struct it points to
+-    customReserved0 @107 :Custom.CustomReserved0;
++    steeringInfo @107 :Custom.SteeringInfo;
+     customReserved1 @108 :Custom.CustomReserved1;
+     customReserved2 @109 :Custom.CustomReserved2;
+     customReserved3 @110 :Custom.CustomReserved3;
+```
+
+---
+
+Example
+---
+```python
+import iqpilot.cereal.messaging as messaging
+
+# in subscriber
+sm = messaging.SubMaster(['sensorEvents'])
+while 1:
+  sm.update()
+  print(sm['sensorEvents'])
+
+```
+
+```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)
+```