minLatency() in osmo-trx

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 &lt;laforge(a)gnumonks.org&gt; http://laforge.gnumonks.org/ ============================================================================ "Privacy in residential applications is a desirable marketing option." (ETSI EN 300 175-7 Ch. A6)