Re: [PATCH] can: sja1000: Add support for listen-only mode and one-shot mode

[Marc Kleine-Budde <mkl@pengutronix.de>]

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On 09/18/2012 06:16 PM, Ira W. Snyder wrote:
[...]

>>> The commit message is incomplete and confusing, I agree. The patch
>>> obviously implements listen-only and one-shot mode. From the data sheet:
>>>
>>> LOM FUNCTION:
>>>    1: listen only; in this mode the CAN controller would
>>>    give no acknowledge to the CAN-bus, even if a message is received
>>>    successfully; the error counters are stopped at the current value
>>>    normal
>>>
>>> Single-shot:
>>>    Setting the command bits CMR.0 (TR) and CMR.1 (AT) simultaneously
>>>    results in sending the transmit message once. No re-transmission will
>>>    be performed in the event of an error or arbitration lost
>>>    (single-shot transmission).
>>
>> The limitation is that when a one-shot message transmission fails, a 
>> Transmit Interrupt is generated and as a consequence can_get_echo_skb is 
>> called. Thus a can frame is echoed back even when the transmission fails 

The question is, can you identify somehow if the message has been
transmitted successfully or not.

>> (instead of being discarded). When one-shot mode is enabled no other 
>> interrupts are generated on a failed transmission. Thus, as far as I can 
>> see, there is no way for the failed frames not to be echoed back locally 
>> in this case.

> I worked around this limitation in the janz-ican3 driver by writing my
> own version of the can_put_echo_skb() and can_get_echo_skb() functions.
> Also notice the skb_dequeue() in ican3_handle_cevtind(), which handles
> the transmission failure case.
> 
> It is probably possible to modify the SJA1000 driver to do something
> similar.

Marc
-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
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