Re: [PATCH 3/3] can: janz-ican3: add support for one shot mode

["Ira W. Snyder" <iws@ovro.caltech.edu>]

On Fri, Jul 13, 2012 at 10:59:18AM +0200, Marc Kleine-Budde wrote:
> On 07/12/2012 06:15 PM, Ira W. Snyder wrote:
> > From: "Ira W. Snyder" <iws@ovro.caltech.edu>
> > 
> > The Janz VMOD-ICAN3 hardware has support for one shot packet
> > transmission. This means that a packet will be attempted to be sent
> > once, with no automatic retries.
> > 
> > The SocketCAN core supports this mode using CAN_CTRLMODE_ONE_SHOT.
> 
> What happens to the queued to-be-echoed CAN frames if the device fails
> to send a CAN frame, due to one shot mode?
> 

I borrowed the hardware and tested this. I generated bus problems by
unplugging the cable from the card.

With "berr-reporting off" I get no indication from the firmware that
there is any problems until ERROR-WARNING (96 errors) or ERROR-PASSIVE
(128 errors) state is reached.

With "berr-reporting on", I get a bus-error message for every message I
try to send. It looks like this:

  can0  20000088  [8] 00 00 80 19 00 00 08 00   ERRORFRAME
        protocol-violation{{error-on-tx}{acknowledge-slot}}
        bus-error
        error-counter-tx-rx{{8}{0}}

The TX error count increases by 8 for each packet. My CAN book seems to
say this is the correct behavior when the bus is unconnected.

I fixed the echo skb problem (see my patch in reply to this) by always
enabling bus errors, and using those to know when packet transmission
failed. In testing, it works well. Please take that patch instead of
this one.

Thanks for the review.

Ira

> Marc
> -- 
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