[Ovmsdev] CAN-3 broken again?

Michael Balzer dexter at expeedo.de
Sun Jan 14 00:24:33 HKT 2018

Part one (TX queue) done & pushed.

OVMS > can can1 status
CAN:       can1
Mode:      Active
Speed:     500000
Rx pkt:                  236657
Rx err:                       1
Rx ovrflw:                    0
Tx pkt:                  106378
Tx delays:                    4
Tx err:                       0
Tx ovrflw:                    0
Err flags: 0x800caa

TX performance is rock steady on can1 -- the delays occurred when sending the stop charge request (as expected). I can't test can2/3, Greg & Geir, could you…?

The TxCallback can't be used on the mcp2515. The ISR can't query the IRQ register, so the TX IRQs are now also handled by the RxCallback(). As the TX IRQs need
to be cleared before loading the next frame, this needs another SPI call. I hope that doesn't introduce new problems.

No changes are necessary to the application code (well, except you can remove any hard coded delays now). The TX queue has a length of 20 frames and will
automatically be used by the drivers when no TX buffers are free.

If an application wants to know whether a frame was sent immediately or gets delayed it can check the return code of the Write() method. Write() now also can
take a second parameter for the maximum wait time for space in the TX queue to become available if it's full (default 0 = fail immediately if queue is full).

I also added logging of CAN errors. It's currently activated by "can … trace on", I don't think this needs to be active by default, just for CAN issue debugging.

E (45718) can: Error can1 rxpkt=3 txpkt=0 errflags=0x800caa rxerr=1 txerr=0 rxovr=0 txovr=0 txdelay=0
E (83528) can: Error can1 rxpkt=7483 txpkt=226 errflags=0x800caa rxerr=1 txerr=0 rxovr=0 txovr=0 txdelay=0

…that's also a first part of the logging extension (part two).


Am 12.01.2018 um 19:01 schrieb Michael Balzer:
> Yes, I had something like that in mind. On TX IRQ, the drivers send CAN_txcallbacks to the CAN_rxtask. The CAN_rxtask then fetches frames from the TX queue
> and calls the TxCallback until all TX buffers of the driver are full. From the already existing TxCallback() stubs I suppose you had planned a scheme like
> that already? ;)
> Greg, can you create a pull request for your MCP2515 change? I'd like to merge that before beginning on the drivers.
> Thanks,
> Michael
> Am 12.01.2018 um 01:19 schrieb Mark Webb-Johnson:
>> Option B sounds like a good approach.
>> Presumably we are just polling the tx queue in the existing CAN_rxtask based on TxCallback?
>> Regards, Mark.
>>> On 11 Jan 2018, at 8:42 PM, Michael Balzer <dexter at expeedo.de <mailto:dexter at expeedo.de>> wrote:
>>> Greg, Mark,
>>> I can check your new code after work.
>>> For the TX performance/overflow issue, there are basically two options:
>>>   * A: make all application TX be aware of overflows, i.e. check the return value of the CAN Write() call as necessary and/or introduce sufficient delays
>>>     (very ugly)
>>>   * B: add a TX queue to the CAN framework, so the application can just push some frames as fast as it likes, with an option to wait/block/fail if the queue
>>>     is full
>>>       o → the framework checks for TX buffers becoming available *(i.e. driver issuing a TxCallback request)* and delivers queued frames only as fast as the
>>>         driver can handle them
>>> Option B has been on my todo list since removing the delay from the MCP driver and introducing the TX buffer check in the esp32can driver, as I don't think
>>> applications should need to handle TX overflows.
>>> I can try to implement that this weekend if it's urgent now.
>>> Regards,
>>> Michael
>>> Am 11.01.2018 um 05:55 schrieb Greg D.:
>>>> Hi Mark, Micheal,
>>>> Ok, good news and bad news.
>>>> Good news:  Rx problem I believe is fixed.  Return is true only if we received something, else false.  And the other interrupt conditions are handled at
>>>> the same time, so no hangs are seen when restarting wifi.  Rx overflow counter does increment properly.  Yea!  Code has been pushed to my clone on Github.
>>>> Bad news:  I am still able to hang the bus, but I think it's on the transmit side.  The obd2ecu process can send up to 3 frames back to back to report the
>>>> ECU Name, followed soon after by several more with to grab the VIN.  Without any flow control on the transmit side, and with a half-duplex CAN bus, that's
>>>> just too much.  Turning off the VIN reporting (config set obd2ecu private yes) seems to let everything run because I don't respond to the VIN request
>>>> (which lets everything drain as OBDWiz times out).  Also verified by putting temporary delays in the obd2ecu code to let things drain a bit between
>>>> frames.  So, the transmit side is still a bit fragile, depending on timing.  Not sure quite what to do here, as there is no easy place to queue things... 
>>>> Do we need to go back to the old way with a delay in the obd2ecu code (perhaps better than in the driver, no?).  Architecturally it's ugly, but this only
>>>> occurs at startup, and I don't mind the kludge.  Do any other uses of the MCP busses do a burst of transmitting?  If not, I'll put the delays in the
>>>> obd2ecu code and call it close enough.  Lemme know.
>>>> For receive, I'd go with what I have for now, if Michael would be so kind as to review what I have done first. 
>>>> https://github.com/bitsofgreg/Open-Vehicle-Monitoring-System-3/blob/master/vehicle/OVMS.V3/components/mcp2515/mcp2515.cpp  Hopefully he'll be back on line
>>>> before I get up in the morning.  Wonderful how the Earth's spin helps with the teamwork.
>>>> I'll keep poking at things tonight, and take it out for a spin in the car tomorrow, just to see everything working together.  But as it is now, it's much
>>>> better than it was before.  Really, this time.  :)
>>>> Greg
>>>> Greg D. wrote:
>>>>> Hi Mark,
>>>>> I believe you are right about the multiple flags, and the code only processing Rx and "error" separately.  Fundamentally, a roll-over from buffer 0 to
>>>>> buffer 1 isn't really an error, just a statement of fact on what happened.  So, we should have buffer 1 and the rollover flag at the same time, which in
>>>>> fact is what I saw.  I need to handle the Rx overflow at the same time as the buffer 1 receive, I think...
>>>>> I need to grab some dinner, but have a fix in the works.  Will report back in a few hours, hopefully with good news...
>>>>> Greg
>>>>> Mark Webb-Johnson wrote:
>>>>>> The design of the system is as follows:
>>>>>>   * The can object CAN_rxtask listens on the rx queue to receive instructional messages from canbus drivers. These can be:
>>>>>>       o CAN_frame: simply passes an entire incoming can frame to the IncomingFrame handler.
>>>>>>       o CAN_rxcallback: an instruction for the CAN_rxtask to call the RxCallback task repeatedly.
>>>>>>       o CAN_txcallback: an instruction for the CAN_rxtask to call the TxCallback once.
>>>>>>   * In the case of CAN_rxcallback, the canbus object RxCallback function is expected to return FALSE to indicate nothing should be done and RxCallback
>>>>>>     should not be called again, or TRUE to indicate an incoming frame has been received and should be passed to IncomingFrame.
>>>>>>   * The system is arranged so that individual bus driver interrupt implementations can be fast and efficient.
>>>>>>       o The driver can choose to receive the frame in the interrupt handler itself, and pass it with CAN_frame to CAN_rxtask. The esp32 can driver uses
>>>>>>         this option.
>>>>>>       o Or the driver can choose to delay the reception of the frame to the RxCallback stage, and merely pass an indication with CAN_rxcallback. The
>>>>>>         mcp2515 driver uses this option.
>>>>>>   * The true/false response from RxCallback is designed to allow the callback to signal it received a frame or not. If it received a frame, then it is
>>>>>>     called again.
>>>>>>   * This approach is used in order to be able to centralise the reception of CAN frames to one single task (avoiding having to run individual tasks for
>>>>>>     each canbus, hence saving stack RAM).
>>>>>> The RxCallback should definitely ONLY return true if an actual can message has been received, and is being passed back in the frame pointer parameter.
>>>>>> I suspect the issue is that the mcp2515 RxCallback is being faced with multiple error flags. Changing that to a return true (as Greg has done) has the
>>>>>> undesired side-effect of issuing a spurious IncomingFrame (with garbage/blank frame), but also causes the RxCallback to be called again (clearing the
>>>>>> error flag). Perhaps the solution is to put a loop in RxCallback so that if an error condition is found, it should be cleared, but then loop again and
>>>>>> keep clearing errors until no more are found, then return false? I think that in the mcp2515 case, this error clearing loop can be simply handled in the
>>>>>> RxCallback itself.
>>>>>> The alternative is to change the RxCallback logic so that the return bool value means simply ‘loop’ (call me again, please), and have the RxCallback
>>>>>> itself call IncomingFrame(), rather than passing a frame as a parameter. If Michael/Greg think this is a better approach, I am happy to make that change
>>>>>> - it is pretty trivial.
>>>>>> Regards, Mark.
>>> -- 
>>> Michael Balzer * Helkenberger Weg 9 * D-58256 Ennepetal
>>> Fon 02333 / 833 5735 * Handy 0176 / 206 989 26
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> -- 
> Michael Balzer * Helkenberger Weg 9 * D-58256 Ennepetal
> Fon 02333 / 833 5735 * Handy 0176 / 206 989 26
> _______________________________________________
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Michael Balzer * Helkenberger Weg 9 * D-58256 Ennepetal
Fon 02333 / 833 5735 * Handy 0176 / 206 989 26

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