I'm using the FMCOMMS3 board and am able to generate a signal but how do I stop the DAC after it starts transmitting? I've tried the dac_stop() function but that does not work.
There are multiple ways - the common ones:
1) Use TDD mode - and move ENSM between Tx <-> ALERT <-> RX
2) In FDD mode insert ZEROs into the DMA stream - or set the channel MUX that selects between DMA, DDS to ZERO. This will also insert Zeros.
I tried to use dac_datasel(ad9361_phy, 0, DATA_SEL_ZERO) but there were random spurs around the previous carrier frequency. Is this the correct function to set the channel mux?
That's the proper function to set the MUX.
But be aware - this mux is available on a per channel basis.
So for a complete TX you have to set the mux for I and Q.
Retrieving data ...