Thanks for the tip! I finally got the time to mess with this again and tried all permutations I could think of. However:
arecord --verbose -f S8 -r 48000 -D plughw:CARD=MNTREFORM2BPICM,DEV=3 mon.wav
arecord: set_params:1456: Unable to install hw params:
ACCESS: RW_INTERLEAVED
FORMAT: S8
SUBFORMAT: STD
SAMPLE_BITS: 8
FRAME_BITS: 8
CHANNELS: 1
RATE: 48000
PERIOD_TIME: 125000
PERIOD_SIZE: 6000
PERIOD_BYTES: 6000
PERIODS: 4
BUFFER_TIME: 500000
BUFFER_SIZE: 24000
BUFFER_BYTES: 24000
TICK_TIME: 0
I tried different DEV values and different formats (just for the sake of trying), but I always get the same error message and no output file is written.
Is there some introspection in the system, i.e. a way to find out what the HW supports similar to how arecord would suggest supported formats?