Re: [SocketCan] Problem of accuracy

[Wolfgang Grandegger <wg@grandegger.com>]

On 07/09/2012 01:57 PM, Mohamed HAMZAOUI wrote:
> If i have understood you correctly, I think it must change the period
> if the write function is a synchronous call !
> if my function is like this :
> 
> while(1)
> {
>     nannosleep(1000000);
>     write (myFrame in opened CAN socket);
> }
> 
> then the result is 1ms + timeOf (write) for every iteration.

Yep.

> but if the write call is asynchronous we return to case you mentioned !

The write call is asynchronous and I'm surprised that it takes 300us to
return. Could you show us your test program?

> Is this correct ?

Anyway, in a previous mail you wrote:

> i use clock_nanosleep with (1000000 ns = 1ms) and the result mesured
> with another CAN transeiver is an average of 1.30 ms (delta = 300 µs)
> !

You cannot expect precises timing with nanosloeep(). Have a look to
cyclictest.c to understand how to implement a periodic task.

Wolfgang.