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     ucom — USB tty support


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

           device ucom

     Alternatively, to load the driver as a module at boot time, place the following line in



     The ucom driver attaches to USB modems, serial ports, and other devices that need to look
     like a tty.  The ucom driver shows a behavior like a tty(4).  This means that normal
     programs such as tip(1) or ppp(8) can be used to access the device.


     The following variables are available as both sysctl(8) variables and loader(8) tunables:

             Debug output level, where 0 is debugging disabled and larger values increase debug
             message verbosity.  Default is 0.

             When set to 1, the ucom driver will mark terminals as console devices when operating
             in device mode.  Default is 1.

             Enables and configure PPS capture mode as described below.

Pulse Per Second (PPS) Timing Interface

     The ucom driver can capture PPS timing information as defined in RFC 2783.  The API,
     accessed via ioctl(2), is available on the tty device.  To use the PPS capture feature with
     ntpd(8), symlink the tty device to /dev/pps0.

     The hw.usb.ucom.pps_mode sysctl configures the PPS capture mode.  It can be set in
     loader.conf(5) or sysctl.conf(5).  The following capture modes are available:
         0     Capture disabled (default).
         1     Capture pulses on the CTS line.
         2     Capture pulses on the DCD line.


     /dev/ttyU*       for callin ports
     /dev/ttyU*.lock  corresponding callin initial-state and lock-state devices

     /dev/cuaU*       for callout ports
     /dev/cuaU*.lock  corresponding callout initial-state and lock-state devices


     tty(4), uark(4), ubsa(4), ubser(4), uchcom(4), ucycom(4), ufoma(4), uftdi(4), uhso(4),
     uipaq(4), umcs(4), umct(4), umodem(4), umoscom(4), uplcom(4), usb(4), uslcom(4), uvisor(4),


     The ucom driver was adopted from NetBSD in March of 2002.  This manual page was adopted from
     NetBSD by Tom Rhodes <> in April 2002.


     Prior to FreeBSD 6.0 ucom created /dev/ucom? rather than the uniform device names created
     today.  Old scripts must be adjusted accordingly.