(GM-144VBIS+ RC9696/14 (?))
This modem does not(!) use Xon/Xoff flow control. Further, the default modem profile sets ‘&S1’, which makes the modem disable DSR all the time. On systems using the FAS serial driver, this will disable CTS flow control!
So, #define FAX_MODEM_HANDSHAKE "AT\\Q3&S0" in policy.h, do not
define FLOW_SOFT for flow control, and fax sending should work. (It
does for me!) Changing FAX_SEND_BAUD to B19200 is not
necessary, it works with B38400.
Fax receiving... I did not fully test it. It’s somewhat difficult since
that modem insists on using auto-answer, but it should be possible to let
it auto-answer if you set mgetty’s ring counter high enough. Or, you can
trick the modem, by changing mgetty’s answer command (ATA) into
ATS0=1 – upon the next RING, the modem will “auto-answer”.