Hi Brais, On Mon, 2019-02-04 at 18:34 +0100, Brais Ares via USRP-users wrote: > Hello, > > I'm trying to implement an AGC software in our RF application. The > setup is the following: > B200mini > master clock rate: 16 MSPS > fs = 32 KSPS
Are you sure? That's a decimation of 500, 125 of which you're doing with a CIC. 32 kS/s is really an extremely low sampling rate for SDR applications, and there's little reason not to do the resampling with "nicer" software filters on your host PC; even the slowest Linux computer should have plenty CPU power to do that. A higher sampling rate would also allow a much more fine-grained examination of these delays. I'd ask you to examine this option. Generally, in the interest of reproducability: how are you doing that gain step detection, en detail? Best regards, Marcus > Receive samples in blocks of 32k (1 second). > I made a tiny program, where I change rx_gain every 1 seconds (just > after rx_streamer->recv() returns) adding or substracting 30 dB. > To find out when a change in rx_gain actually affects the received > samples I implemented a simple detection algorithm. > > Ignoring the non-deterministic latency, at least I would expect the > time between changes to be 1 seconds as well (µ = 1 seconds, with > some non-zero variance), the same periodicity they were invoked > with. > > However, this change takes on average 1.016 seconds (see figure). > This means for each set_rx_gain call the radio is taking longer and > longer to apply the change (see figure). Example: > > t = 1 s -> Recv previous block and change gain > t = 2 s -> Recv previous block and change gain > t = 1.016 -> Change in gain detected in previous block (OK, latency > to change gain is around ~0.016 ms)16 µs would indeed be a pretty *gp > t = 3 s -> Recv previous nd change gain > t = 2.032 s -> Change in gain detected in previous block (I would > expect ~2.016) > t = 4 s -> Recv previous block and change gain > t = 3.048 s -> Change in gain detected in previous block (I would > expect ~3.016) > (...) > t = 60 s -> Recv previous block and change gain > t = 59.96 s -> Change in gain detected in previous block (After 60th > call to rx_gain, latency has increased to almost 1 second!) > > Is there any rational reason why this is happening? > (I've tried longer periods, up to 10 seconds, with the same result). > > Regards, > Brais. > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com _______________________________________________ USRP-users mailing list USRP-users@lists.ettus.com http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
