On 2022-05-05 10:26, [email protected] wrote:
I wanted to verify something to make sure I understand how things
work. It seems to me that when using an X310 or N320 (the two USRPs I
happen to be messing with), that when I am using both RX channels, if
I change frequencies on on one channel, both will produce time tags in
Gnu Radio. I’ve looked through the uhd and FPGA source code and
haven’t seen anywhere where the two channels are linked together on a
freq change; but I suspect that I missed something and wanted to verify.
Interesting. Time tags are definitely issued whenever there's an
overrun, and if your tuning results in an overrun, you'll also get a
fresh time-tag in Gnu Radio.
Also, it seems like when I change frequencies, I may, or may not, drop
samples. This makes sense and is more prevalent when I am using a
higher sample rate. What is weird to me is that it looks like when I
again change the freq on a single channel, both channels will drop (or
not drop) the same number of samples. I assume that this is to keep
the streams in sync, but again I wanted to verify that.
IN a multi_usrp with multiple channels the streams are conceptually
"multi-channel streams". Since the connection into a single device is
typically arranged as
I1Q2 I2Q2 etc, then packet drops will always end up dropping for both
channels. On top of THAT, yes, the underlying multi_usrp code tries to
keep the channels
aligned after an overrun, etc.
Dropping samples on frequency-change is definitely NOT "by design", but
may emerge as you get close to the limits of the overall radio<---->host
"channel", which includes
not only the raw bit-rate of the underlying transport, but the
ability of the entire "stack" to "keep up".
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