add car porting docs (#30704)

* add car porting docs

* add cabana

* absolute link

* absolute link

* absolute link

* selfdrive/car
old-commit-hash: 595041ffc0

selfdrive/car/README.MD

@@ -1,11 +1,77 @@
-## Port structure
+# selfdrive/car
-##### interface.py
+
+### Checkout this blogpost for a high level overview of car ports
+https://blog.comma.ai/how-to-write-a-car-port-for-openpilot/
+
+## Useful car porting utilities
+
+Testing car ports in your car is very time consuming! Checkout these utilities to do basic checks on your work before running it in your car.
+
+### [Cabana](/tools/cabana/README.md)
+
+View your cars CAN signals through DBC files, which openpilot uses to parse and create messages that talk to the car.
+
+Example:
+```bash
+> tools/cabana/cabana '1bbe6bf2d62f58a8|2022-07-14--17-11-43'
+```
+
+### [selfdrive/debug/auto_fingerprint.py](/selfdrive/debug/auto_fingerprint.py)
+
+Given a route and platform, automatically inserts fw fingerprints from the platform into the correct place in values.py
+
+Example:
+```bash
+> python selfdrive/debug/auto_fingerprint.py '1bbe6bf2d62f58a8|2022-07-14--17-11-43' 'SUBARU OUTBACK 6TH GEN'
+Attempting to add fw version for:  SUBARU OUTBACK 6TH GEN
+```
+
+### [selfdrive/car/tests/test_car_interfaces.py](/selfdrive/car/tests/test_car_interfaces.py)
+
+Finds common bugs for car interfaces, without even requiring a route!
+
+
+#### Example: Typo in signal name
+```bash
+> pytest selfdrive/car/tests/test_car_interfaces.py -k subaru # (replace with the brand you are working on!)
+
+=====================================================================
+FAILED selfdrive/car/tests/test_car_interfaces.py::TestCarInterfaces::test_car_interfaces_165_SUBARU_LEGACY_7TH_GEN - KeyError: 'CruiseControlOOPS'
+
+```
+
+### [selfdrive/debug/test_car_model.py](/selfdrive/debug/test_car_model.py)
+
+Given a route, runs most of the car interface to check for common errors like missing signals, blocked panda messages, and mismatches.
+
+#### Example: Panda safety mismatch for gasPressed
+```bash
+> python selfdrive/debug/test_car_model.py '4822a427b188122a|2023-08-14--16-22-21'
+
+=====================================================================
+FAIL: test_panda_safety_carstate (__main__.CarModelTestCase.test_panda_safety_carstate)
+Assert that panda safety matches openpilot's carState
+----------------------------------------------------------------------
+Traceback (most recent call last):
+  File "/home/batman/xx/openpilot/openpilot/selfdrive/car/tests/test_models.py", line 380, in test_panda_safety_carstate
+    self.assertFalse(len(failed_checks), f"panda safety doesn't agree with openpilot: {failed_checks}")
+AssertionError: 1 is not false : panda safety doesn't agree with openpilot: {'gasPressed': 116}
+```
+
+
+## Car Port structure
+
+### interface.py
 Generic interface to send and receive messages from CAN (controlsd uses this to communicate with car)
-##### carcontroller.py
+
+### carcontroller.py
 Builds CAN messages to send to car
+
 ##### carstate.py
 Reads CAN from car and builds openpilot CarState message
+
 ##### values.py
-Fingerprints and absolute limits
+Fingerprints, limits for actuation, car doc information, etc
+
 ##### radar_interface.py
-Radar interface
+Interface for parsing radar points from the car