[linux-dvb] help on timing stuff

[Ralph Metzler <rjkm@convergence.de>]

giancarlo@baracchino.it writes:
 > Hi, I would like to know how I can determinate the exact istant when the TS 
 > packet (that matches the currently demux rules) is received in the buffer 
 > of the sat-dvb card or when it is sent to the driver.

No, this is not possible. You do not have direct access to the TS
packets on card.

 
 > I would like also to know if it is possible to get the current status of 
 > the STC.

Possible, but not supported right now and it would not be very
reliable. The time between reading the STC on the AV7110 and getting
it to the PC could vary a lot. You first have to write the STC
somewhere into DPRAM and then send an IRQ to the PC. I don't know what
precision you are after, but it would be nowhere close to the
resolution of the do_gettimeofday timers.
 
 > 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.


Ralph




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