Dear all,
the following question popped up on IRC:
22:08 < roh> is there some documentation how the minLatency() call in osmo-trx
works?
22:10 < roh> it looks to me like the values we use for usrp1 and lms are not
correct/cargocult
I agree, the values are likely wrong for the non-UHD devices.
Interestingly, they are auto-tuned at runtime, see the following piece in
Transceiver.cpp:
// if underrun hasn't occurred in the last sec (216 frames) drop
// transmit latency by a timeslot
if (mTransmitLatency > mRadioInterface->minLatency()) {
if (radioClock->get() > mLatencyUpdateTime + GSM::Time(216,0)) {
mTransmitLatency.decTN();
LOG(INFO) << "reduced latency: " << mTransmitLatency;
mLatencyUpdateTime = radioClock->get();
}
}
However, that block only applies to devices with TX_WINDOW_USRP1 set, that is
USRP1, B100 and B2xx devices.
In fact, I cannot find any user of the minLatency() method outside the context
of TX_WINDOW_USRP1, and hence I think it doesn't matter what kind of magic
value the LMS driver supplies?
So at least I conclude:
* it's only ever used on USRP1, B100 and B2xx, and it is dynamically adjusted
at runtime on those platforms
Regards,
Harald
--
- Harald Welte <[email protected]> http://laforge.gnumonks.org/
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