UART0 doesn't recognize char input


I’m trying to use UART0 of 401c (pins 5 & 7 of LS exp con) to control a serial device. UART0 is ttyMSM1 in my Debian build. I can see chars being transmitted to the ext device and they get received by the ext device; but any char that is input to the 410c from the ext device is ignored. I have a really simple test loop using stdin/stdout. I can see chars input to the UART0 via a logic analyzer, but the 410c code just never sees the input chars. I’m using termios and am in a non-canonical mode. I have chmod properties on ttyMSM1 to 0777 but that doesn’t seem to help. Has anyone ever been able to get this work? Can you share some code that does work?


Could you please confirm the peer device (or adapter) uses same 1.8V IO logic levels?

Could you also try with an existing known working tool like minicom or microcom and check I you reproduce this issue?


Yep-the interface is 1.8V on each end. Also, I have been able to see chars transmitted from the 410c. I’m checking the Rx side now.


Update: I can see chars being transmitted TO the UART0 from both a Putty Terminal and then also from an nRF devkit using a 1.8V UART interface; but still the 410c does not ever seem to actually receive the chars. I’m looking now for full feature setup through termios.