[Ovmsdev] CAN callbacks / VW e-Up read/poll via OBD is working

Michael Balzer dexter at expeedo.de
Sun Aug 9 19:04:45 HKT 2020

UpMiiGo guys,

Am 30.07.20 um 14:43 schrieb Soko:
> Can I somehow get called (in my vehicle-class) if an can-error is thrown?
Am 30.07.20 um 16:17 schrieb Michael Balzer:
> CAN tx errors can be caused by other issues as well, so should
> generally not be interpreted that way.

According to Chris on the GE forum, you're also seeing CAN tx errors on
the Komfort CAN bus, so maybe it actually makes sense for you to check
for CAN errors.

There are two options:

 1. Register a TX callback for a specific TX frame
 2. Register a general TX callback

Option 1_ is currently not supported by the poller framework (but could
be added). For a manual frame transmission, simply set the frame
callback pointer to your handler:

static void CAN_tx_callback(const CAN_frame_t* frame, bool success){
  if (!success) {
    // tx failure


  CAN_frame_t txframe;
  txframe = {};
  txframe.MsgID = 0x705;
  txframe.FIR.B.DLC = 8;
  txframe.data = { 0x…, 0x…, … };
  txfrane.callback = CAN_tx_callback;

_Option 2_ uses the same handler signature. A handlers is registered as
a general callback like this, e.g. on vehicle init:

    MyCAN.RegisterCallback(TAG, CAN_tx_callback, true);

You can also register an RX callback by passing "false" or omitting the
third argument. On unloading the vehicle module, simply do:


CAN callbacks are called directly within the CAN driver context prior to
all standard queues, so can be used for very fast CAN responses -- and
thus need to be very fast too, to not affect CAN driver throughput.
Don't do any complex processing in the handler, avoid anything that
could block the task.


Michael Balzer * Helkenberger Weg 9 * D-58256 Ennepetal
Fon 02333 / 833 5735 * Handy 0176 / 206 989 26

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