Re: [Discuss-gnuradio] USRP1 Inband firmware questions

[Eric Schneider]

Correction: As Brian stated, I think 0xffffffff is the correct "NOW"
timestamp.

On Thu, 2010-08-12 at 09:08 -0600, Eric Schneider wrote:
> Sylvain -
> 
> On Thu, 2010-08-12 at 14:27 +0200, Sylvain Munaut wrote:
> 
> >  - How can I know the 'current' TX timestamp ? I want to send a ping
> > command, but I don't see a way to know what timestamp I should use.
> 
> It is in the header of every Rx packet.  If you need to send a command
> without knowing the current timestamp, use timestamp = 0, which will
> always execute immediately.  (There are some caveats which can usually
> be ignored)
> 
> >  - The timestamp seems imprecise: I often get a timestamp difference
> > between two packets of 24191 or 24193  while I should in fact get 24192
> > (I'm at 192 decimation). With such a high decimator, I can fix it up
> > myself, but still, that looks weird.
> 
> Which inband code are you using exactly?  My inband work (which was in
> the ets developer branch) fixed exactly that problem.  The root cause
> was that time-stamping was done after sample buffering, so the stamps
> would vary based on the buffer levels.
> 
> The new code is accurate and reflects the exact value of the 64MHz
> counter for the first sample in the packet.  There is an additional
> offset between rx/tx times at analog due to various signal processing
> stages before the time-stamping (which can vary depending on the FPGA
> configuration).  This value is easily compensated for on the host.
> 
> --Eric S.
> 
> 
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