NMDM(4)                FreeBSD Kernel Interfaces Manual                NMDM(4)

NAME
     nmdm - nullmodem terminal driver

SYNOPSIS
     To compile this driver into the kernel, place the following line in your
     kernel configuration file:

           device nmdm

     Alternatively, to load the driver as a module at boot time, place the
     following line in loader.conf(5):

           nmdm_load="YES"

DESCRIPTION
     The nmdm driver provides two tty(4) devices connected by a virtual "null
     modem" cable.

     If either of the two tty devices have the CDSR_OFLOW bit ("stty dsrflow")
     set in their line discipline, the nmdm device will emulate the speed
     configured in the termios(4) settings.  The speed emulation works
     independently in the two directions, controlled by the slower end's
     termios settings (c_ispeed, c_ospeed, CS5 ... CS8, CSTOPB and PARENB).

FILES
     /dev/nmdmN[AB]                     nullmodem device nodes.  Where the A
                                        node has a matching B node.

     The nmdm driver implements "on-demand device creation" so simply
     accessing a given instance in /dev will create it.

DIAGNOSTICS
     None.

SEE ALSO
     stty(1), termios(4), tty(4), ttys(5)

HISTORY
     The nmdm driver first appeared in FreeBSD 4.4.

FreeBSD 13.1-RELEASE-p6          July 11, 2020         FreeBSD 13.1-RELEASE-p6