Re: [Discuss-gnuradio] USRP1 Inband firmware questions

[Eric Schneider]

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.