osmo-trx: Generating frame sync output on GPIO?

[Harald Welte]

Hi all,

I was wondering if it is possible to generate a TDMA frame sync output
on a GPIO line of a USRP device (and/or any other SDR supported by
osmo-trx).  This way it would be much easier to do e.g. BER testing
by using a pure waveform/pattern generator for the "MS side".  Such
devices (Like an E4433B) can only generate the uplink bursts with
pseudo-random sequence, but they don't have any receiver, so they're not
able to receive the downlink from the BTS in order to lock on the TDMA
frame and transmit the uplink in sync to that.

There are of course specialized devices (CMU-300, ...) or hardware
options that add such receivers for synchronization on the signal
generators, equipment side, but why go there if there would be an easy
way to generate some kind of a frame sync output.

I would appreciate to know even if there's a way to introduce such
"synchronous GPIO toggles" or the like in the command stream to UHD
devices.  If that existed, it should be rather simple to insert those
whenever a new burst for TS0 is sent.

A rather computationally (and bandwidth) expensive other option might be
to use the second RF output to generate such a signal, but I was hoping
not having to abuse the 2nd channel for that ;)

Regards,
	Harald
-- 
- Harald Welte <laforge at gnumonks.org>           http://laforge.gnumonks.org/
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