[Ovmsdev] CAN drivers: fix & harmonize frame transmission failure handling
Michael Balzer
dexter at expeedo.de
Sat Jan 9 01:52:56 HKT 2021
Steve,
thanks, that's perfect. The failure handling works as designed in your case.
Regarding your question:
> It does prompt me to ask a question that I had - On the i3, if you do
> something like send a lock from the key or the Connected Drive APP
> then the OBD-II comes alive but goes asleep again in less than a minute.
>
> if I have a PID that I poll infrequently - say every 120 seconds.
> What happens in this case? Would they be seen as "overdue" when the
> bus comes alive and polled immediately, or is it a matter of luck if
> the 120th tick arrives at a time when the bus is alive?
>
> If the latter I need to poll even things like the VIN every 10 seconds
> to make sure I get it before the bus goes to sleep again.
With the old handling, the queued frames would have get sent as soon as
the bus got awake again. That's nasty, as the frames may have been for a
specific task (e.g. some protocol part), and should not be sent to a
just woken up car. That could produce any sort of problem up to queued
OBD writes corrupting the car memory. It was also nasty the driver would
then send the whole TX queue at once, flooding the bus. A vehicle could
see that as a malicious activity and block access.
The new handling will abort the transmission as soon as the CAN
controller runs into the retransmission limit (128 tries, formally CAN
error-passive mode).
So you now need to "ping" the car with some simple read or session state
request, and check if a response comes in to determine if the bus is
online. If using the poller, you'll get a respective Incoming…()
callback. If you don't use the poller, you can set the TX callback
pointer on the frame you send. The TX callback is called with a success
indicator, so you can know a frame has been sent even if you don't get a
response from the device.
Regards,
Michael
Am 08.01.21 um 09:33 schrieb Steve Davies:
> Hi Michael,
>
> Here's the log from a test on my car with your branch
>
> I started the car, left it for a while, then shut it down and waited
> until the OBD-II first went to "not getting replies to my requests"
> and then to "not sending anything at all".
>
> Hope its helpful.
>
> https://drive.google.com/file/d/1AavD41HCykYrn-BxQXNufu2dT_UVCXYU/view?usp=sharing
> <https://drive.google.com/file/d/1AavD41HCykYrn-BxQXNufu2dT_UVCXYU/view?usp=sharing>
>
> Steve
>
>
> On Fri, 8 Jan 2021 at 08:22, Steve Davies <steve at telviva.co.za
> <mailto:steve at telviva.co.za>> wrote:
>
> Hi Michael,
>
> The change looks helpful, thanks. I'll try it during the course
> of the day.
>
> It does prompt me to ask a question that I had - On the i3, if you
> do something like send a lock from the key or the Connected Drive
> APP then the OBD-II comes alive but goes asleep again in less than
> a minute.
>
> if I have a PID that I poll infrequently - say every 120 seconds.
> What happens in this case? Would they be seen as "overdue" when
> the bus comes alive and polled immediately, or is it a matter of
> luck if the 120th tick arrives at a time when the bus is alive?
>
> If the latter I need to poll even things like the VIN every 10
> seconds to make sure I get it before the bus goes to sleep again.
>
> Thanks,
> Steve
>
>
> On Thu, 7 Jan 2021 at 18:22, Michael Balzer <dexter at expeedo.de
> <mailto:dexter at expeedo.de>> wrote:
>
> Everyone,
>
> please pull & test the new "can-txfail-fix" branch. It's up to
> date and includes the BMW i3 code already.
>
> I need to get feedback from users of both can1 (esp32can) &
> can2/3/4 (mcp2515), as changes had to be made to both drivers.
>
> I'll quote from my commit:
> https://github.com/openvehicles/Open-Vehicle-Monitoring-System-3/commit/c94592a11ad2c989e65313d23a8876cf38787d70
> <https://github.com/openvehicles/Open-Vehicle-Monitoring-System-3/commit/c94592a11ad2c989e65313d23a8876cf38787d70>
>
> Design goals:
> - any TX can either fail or succeed, the result state is terminal
> - the respective TX callback is called exactly once
> - transmissions fail on reaching the error-passive bus state
> and on message/bus errors while in error-passive state
> - a failed TX will be aborted (no retries after bus recovery),
> i.e. will be retried at most 128 times (in error-active phase)
> - reduce excessive CAN error logging
> - reduce excessive interrupt load with switched-off buses
>
> This results in the application being able to reliably detect a
> switched-off vehicle bus by the TX callback's success indicator.
> It also results in frames no longer being held in the TX buffer
> or added to the TX queue when the bus is switched off. The
> application can now rely on getting a clean bus state on every
> reconnect, without any queued old frames to be sent automatically.
>
> Secondary benefit from aborting the transmission is, the module
> doesn't need to handle the load from the continuously triggered
> CAN error interrupts by retransmission attempts in error-passive
> state.
>
>
> Reason for this was a) Steve's question on aborting
> transmissions / flushing the queue and b) my new car now also
> switching off the bus, with the annoying effect of a frozen
> can1 every 2-3 days, needing to reboot the module. I'm not
> sure yet if the freeze issue is solved, but I haven't had it
> since running these changes on my module.
>
> The other issue of the transceivers resending frames queued
> long ago may have caused all sorts of strange & unrepeatable
> issues. I remember the VW crew having problems that fell into
> this category.
>
> I've verified the new MCP2515 implementation only on my
> workbench (with an Arduino as the CAN tester), so real life
> tests are necessary.
>
> Thanks,
> Michael
>
> --
> 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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