RM502 sends always zeroes to o PCM stream


Having RM502QGLAAR11A02M4G_01.200.01.200. After answering the call with ATA second USB port (USB PCM audio port) sending only zeroes. The actual RX PCM voice data expected. How to fix ?

P.S. I’m using CS voice, i.e.


P.P.S Reproduce steps: start in Linux hex monitoring of voice port with tio - “tio -h /dev/voice_port”, call number, answer with ATA. Observe running zeroes in terminal instead live PCM data. Actual call is working as I can send DTMF’s with AT+VTS and can hear them from other side of call

BTW: Generating local DTMF’s with AT+QLDTMF do not produce anything at USB PCM voice port. I think this is bug