commaai
VW PQ: Extended standstill for FtS with EPB
Description
Certain VW PQ (Sharan, perhaps others) equipped with electric parking brakes are able to stay at standstill more than the usual three seconds. Their stock ACC makes use of this. This is still only Follow-to-Stop, they still need gas pedal input to leave.
Under openpilot longitudinal, the same cars were going to an ACC faulted state after three seconds of standstill. We analyzed the differences, and found the problem was too much requested negative acceleration at standstill.
The VW port has never made intentional use of CarParams.stopAccel: we inherit the default -2.0 from interfaces.py and the car starts ignoring the accel request as soon as we set the stopping control bits. Only this subset of VW PQ seems to care. The value it wants is closer to stock ACC behavior for both MQB and PQ, so we'll just make the change across the board.
Verification
Extensive testing and troubleshooting by @jackking444, thank you! One step closer to SnG with comma pedal.
A process_replay delta is expected for VW MQB due to the CarParams change. VW PQ is still in dashcam.
Route
stock: e12eb71c201af95a|2023-03-24--13-56-39
openpilot before: e12eb71c201af95a|2023-05-16--02-18-31
openpilot after: e12eb71c201af95a|2023-05-19--16-09-09
