W dniu 17.07.2016 o 13:05, Piotr Krysik pisze: > W dniu 07.06.2016 o 13:30, Piotr Krysik pisze: >> W dniu 01.10.2015 o 14:46, Piotr Krysik pisze: >>> W dniu 25.09.2015 o 23:23, Tom Rondeau pisze: >>> >>> >>> >>> Looking at the block, I was hoping it was as easy as putting a >>> set_relative_rate call in the set_resamp_rate to adjust how the tags >>> are being propagated. But it's not that simple. See Issue #846 >>> (http://gnuradio.org/redmine/issues/846) for details on the problem. >>> >>> Tom >>> >>> >> Hi, >> >> I'm writing to let everyone know that resampling blocks after changing >> the resampling rate in the run-time is still eating stream tags. This >> makes some designs impossible to implement currently. >> >> For example - it would be great if it was possible to implement a clock >> offset frequency correction like I have drawn on the attached image: >> -there are two blocks that do the correction: resampler and frequency >> shifting block, >> -they change their parameters (resamp_rate, frequency_shift) on stream tags, >> -there is a block that does clock frequency offset measurements that is >> connected at the end (putting it in different place is not practical in >> many circumstances), >> -these measurements are sent to frequency offset control block which >> turns them into control messages addressed for both resampler and >> frequency shifter, >> -msg to tag blocks adds a tag containing a control message to a stream, >> -the information about changes of settings of the resampler and rotator >> are interpreted also by the measurement block, that adjusts measurements >> based on this information. >> >> But currently it not possible to do this due to the issue with the >> resampling blocks. >> >> Did you Tom or anyone found the source of the problem? >> >> > Hi Tom and others, > > I implemented fractional resampling block that can have resampling rate > changed. > > When doing this I learned what is the source of the issue #846. The > mistake is following: > > transformation of tag offset by resampling block that changes its > resample rate is not a linear function, so in this case you can't use > such simple linear conversion, like it is done in GNU Radio's runtime: > https://github.com/gnuradio/gnuradio/blob/master/gnuradio-runtime/lib/block_executor.cc#L143 > > However, transformation is linear from one resample rate change to > another. So if you know input and output sample number for which > resample rate was the same as for the moment when a tag came - you can > use this as reference point to compute the tag's offset at the output of > the resampling block. > > > My proposed solution: modification of tags offsets processing in > gnuradio runtime so it includes case when you have resampling blocks > with dynamically changing resample rate doesn't seem resonable. If would > complicate things too much because the runtime would have to track > resample rate changes inside of every block that can do that. Resampling > blocks that can have resample rate changed dynamically should implement > tags propagation themselves. > > Current fractional resampler block doesn't do that and it is incorrect. > The input for dynamic resample rate control should be removed as it can > cause problems to the users OR users should be warned that if they use > this input they shouldn't expect tags to work correctly. > > The block implemented by me is available here: > https://github.com/ptrkrysik/gr-gsm/blob/master/lib/misc_utils/controlled_fractional_resampler_cc_impl.cc > > It uses a pmt pair ("set_resamp_ratio",value) tag to set resample ratio > precisely at the moment of tag occurrence. > It wasn't tested in all possible conditions yet, so I'm still a bit > cautious regarding it. But it presents how such a block can be > implemented and in tests performed by me it worked (it is also now used > to correct sample frequency offset in gr-gsm). > Hi all,
Little update in this old but still valid thread. I created two issues regarding it: 1. what is wrong in the runtime in the context changing relative rate and tag propagation: https://github.com/gnuradio/gnuradio/issues/2055 2. other things regarding tag propagation that are wrong in mmse_resampler (new name of fractional_resampler): https://github.com/gnuradio/gnuradio/issues/2056 Best Regards, Piotr Krysik _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
