[op25-dev] OP25 working with UHD and GRC [2 Attachments]

Hi folks, I had the pleasure of sitting with some major OP25 contributors (Max and Mike) at the GNU Radio conference today, and also managed to get OP25 working with a USRP N210 using UHD. You can see in the attached image that I'm using the OP25 block from gr-baz in GRC (the flowgraph sends the decoded audio to the speakers via the Audio Sink). The voice frames' data is being printed in the console, and four-level dibits are shown on the scope. The other tabs contain FFTs for the entire baseband and the selected channel, and make use of the new click-handler feature that triggers a callback containing the frequency you clicked on. You can therefore tune (really change the offset in the Freq Xlating Filter) to a signal you see appear on the FFT just by clicking on it (the same way you can with the Python apps, e.g. usrp_p25_rx/audio_p25_rx, however this is all from GRC). The IT++ 4.2 BCH problem still exists, so I've used the alternate implementation that Max also uses in the 'repeater' code to handle identification of the frame header. The GRC flowgraph obviously uses the UHD Source block to capture the baseband data, but the Python scripts (e.g. those mentioned above) also now work with UHD. The legacy USRP code is actually untouched as I've written a thin wrapper for UHD that makes any UHD-compatible device accessible through the legacy interface (i.e. brought 'from gnuradio import usrp' & usrp.source_c back). Not the best approach to force projects to move to UHD properly, but a temporary measure in the meantime ;) I'll post some code soon! Kind regard, Balint