nmdm — nullmodem terminal driver

       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 (“sttydsrflow”) 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).

       None.

/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.

       The nmdm driver first appeared in FreeBSD 4.4.

Debian                                          January 23, 2018                                         NMDM(4)

       nmdm — nullmodem terminal driver

stty(1), termios(4), tty(4)

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

             devicenmdm

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

             nmdm_load="YES"