🚀 go-pugleaf

In article <325@nsta.UUCP> amos%nsta@nsc.com (Amos Shapir) writes:
>One of the optional flags of the c_cflag field of termio is CLOCAL. (see
><termio.h>)  It is  supposed  to  cause the  tty  driver  to ignore  the
>'carrier detect' bit  in the RS232 interface, and open  the line anyway.
>This is needed for  ports that do not have the DC  wired; trying to open
>such a port without setting the CLOCAL bit first, will cause the open to
>hang forever waiting for a carrier signal.
>
>However, the  only way to set  this flag is  by a ioctl call;  the ioctl
>call needs  a file-descriptor  argument; a  file-descriptor can  only be
>obtained by a successfull open call...
>
>The  only solution  if you  don't have  sources is  to re-wire  all your
>terminal plugs by shorting CD to DTR or something like that.

The solution is to open the file with the O_NDELAY bit set (eg.
fd = open(file, O_RDWR | O_NDELAY)).  O_NDELAY allows the open to
complete without waiting for carrier.  Next, do a TCGETA ioctl
to get the current settings (ioctl(fd, TCGETA, &term)), turn on
the CLOCAL flag (term.c_flag |= CLOCAL) and do a TCSETA ioctl.
Now the port is open and modem control lines will be ignored.

--------------------------------------------
Robert (ain't got no cute sayings in my signature) Rother
rmr@sdcsvax.UCSD.EDU or sdcsvax!rmr