I've been looking into this a bit. The way that dstar works is different from p25/ysf/dmr in that dstar uses gmsk. There is a gmsk demod block in native gnuradio, but I'm dissatisfied with its performance as it apparently doesn't handle frequency offsets at all gracefully. If there is any frequency drift (due to, say, ppm error in the rtl sdr) it will stop working due to that lack of frequency synchronization.Thanks for the update, Max. Any ETA on that fix ?
The OP25 demod block in any case needs to be enhanced to add gmsk as a valid filter type. I guess the sequence of steps might be roughly to add dstar initially using the gr native gmsk block and then fix the other issues. It's less than ideal...