Re: c_can driver sometimes sends first two bytes filled with zeros

[Thor Thayer <tthayer@opensource.altera.com>]

Hi Richard,

On 05/12/2016 04:23 AM, Richard Andrysek wrote:
> We can reproduce an issue with the canutils. We send messages in the loop with non-zero bytes and from time to time we get first two bytes of the message with zero values. The test script looks so:
>
> #!/bin/sh
>
> echo "Press [CTRL+C] to stop.."
> while true
> do
>                 cansend can1 --loop=15 -i 933 0xde 0xde 0xde 0xde 0xde 0xde
> done
>
> With CAN analyzer we see normally the right message, but in cycles ~1min we see first two bytes are zero.
>
> If we add some delays between messages, like this:
>
> do
>                 cansend can1 --loop=1 -i 933 0xde 0xde 0xde 0xde 0xde 0xde
>                 usleep 5
> 	cansend can1 --loop=1 -i 933 0xde 0xde 0xde 0xde 0xde 0xde
>                 usleep 5
> 	cansend can1 --loop=1 -i 933 0xde 0xde 0xde 0xde 0xde 0xde
>                 usleep 5
> 	cansend can1 --loop=1 -i 933 0xde 0xde 0xde 0xde 0xde 0xde
>                 usleep 5
> 	cansend can1 --loop=1 -i 933 0xde 0xde 0xde 0xde 0xde 0xde
>                 usleep 5
> 	cansend can1 --loop=1 -i 933 0xde 0xde 0xde 0xde 0xde 0xde
>                 usleep 5
> 	cansend can1 --loop=1 -i 933 0xde 0xde 0xde 0xde 0xde 0xde
>                 usleep 5
> 	cansend can1 --loop=1 -i 933 0xde 0xde 0xde 0xde 0xde 0xde
>                 usleep 5
> 	cansend can1 --loop=1 -i 933 0xde 0xde 0xde 0xde 0xde 0xde
>                 usleep 5
> 	cansend can1 --loop=1 -i 933 0xde 0xde 0xde 0xde 0xde 0xde
>                 usleep 5
> 	cansend can1 --loop=1 -i 933 0xde 0xde 0xde 0xde 0xde 0xde
>                 usleep 5
>
> done
>
> It works fine.
>
> We use Altera Cyclone V, where the  c_can driver is used. It runs with Linux kernel 3.16, but I've checked 4.5 version of a driver and it is a same one.
>
> Have somebody idea how to find a reason for that?
>
> Richard
>
How old are your canutils? I had a similar issue on an older version of 
cansend (4.0.6 from the Pengutronix site - with a copyright date of 2009).

There is an old thread (http://comments.gmane.org/gmane.linux.can/2339) 
that suggests adding a delay in the cansend utility to work around a 
poll/select bug.

I added a delay for 4.0.6 but you may want to grab the latest from 
github (https://github.com/linux-can/can-utils).

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