COM(4)

NAME
com - serial communications interface

SYNOPSIS
com0 at mainbus? base 0x00210fe0
com1 at mainbus? base 0x00210be0

DESCRIPTION
The com driver provides support for NS8250-, NS16450-, and NS16550-based EIA RS-232C (CCITT V.28) communications interfaces. The NS8250 and NS16450 have single character buffers, and the NS16550 has a 16 character buffer.

Input and output for each line may set to one of following baud rates; 50, 75, 110, 134.5, 150, 300, 600, 1200, 1800, 2400, 4800, 9600, 19200, 38400, 57600, or 115200, or any other baud rate which is a factor of 115200.

If “flags 1” is specified, the com driver will not set the MCR_IENABLE bit on the UART. This is mainly for use on AST multiport boards, where the MCR_IENABLE bit is used to control whether or not the devices use a shared interrupt.

FILES

/dev/tty00

/dev/tty01

DIAGNOSTICS

com%d: %d silo overflows The input “silo” has overflowed and incoming data has been lost.

com%d: weird interrupt: iir=%x The device has generated an unexpected interrupt with the code listed.

SEE ALSO
tty(4)

HISTORY
The com driver was originally derived from the i386 com driver and is

BUGS
Data loss is possible on busy systems with unbuffered UARTs at high speed.

The name of this driver and the constants which define the locations of the various serial ports are holdovers from DOS.