[linux-dvb] Re: help on timing stuff

[GB <giancarlo@baracchino.it>]

At 00.51 20/09/2001, you wrote:
>  > My target is to determinate the exact receiving time istant in order to
>  > estimate the jitter on the packets. I know that a good correction of the
>  > jitter is obtained from  "max(PCR - STC)" but I would like to follow
>  > another "kernel" way (do_gettimeofday at every TSP receved with the same
>  > pid, and then subtract).
>
>The AV7110 does not have a do_gettimeofday(). Of course it has timers,
>but certainly not as precise as the built-in ones of Pentium processors.
>And, as I said, you don't have direct access to the TSP arrival times.

Ok, suppose that I make a software PLL that emulates the internal 27mhz 
clock... maybe I can estimate the jitter only by make difference between 
the "virtual clock" and the just received PCR. It will bring the "software" 
delay, but once determinate, it can be subtracted.
What scares me is the possibility that sometimes a packet takes time X for 
being received by the software, and sometimes in takes X+Y for being 
received. Maybe if I write a kernel module instead of a user program, I can 
be sure that the software delay will be constant.


May it works?


--------------------------------------------
Giancarlo Baracchino
student at Telecommunications Engineering, Pisa
mobile: +39 338 2200917
--------------------------------------------



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