COM(4)

NAME
com - serial communications interface

SYNOPSIS
com0 at isa? port "IO_COM1" irq 4
com1 at isa? port "IO_COM2" irq 3
com* at acpi?
com* at cardbus?
com* at isapnp?
com* at mca? slot ?
com* at mhzc?
com* at ofisa?
com* at pcmcia?
com* at pcmcom?
com* at pnpbios? index ?
com* at puc? port ?
options COM_HAYESP
options RND_COM

  Arm32
com0 at mainbus? base 0x00210fe0
com1 at mainbus? base 0x00210be0

  HP 9000/300 and 400 Series
com* at dio? scode ?
com* at frodo? offset ?

  IBM PowerPC 4xx
com* at opb?

  SPARC
com* at ebus?
com* at obio0

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.

The ttyXX devices are traditional dial-in devices; the dtyXX devices are used for dial-out. (See tty(4).)

The COM_HAYESP kernel option adds support for the Hayes ESP serial board.

With options RND_COM enabled, the com driver can be used to collect entropy for the rnd(4) entropy pool. The entropy is generated from interrupt randomness.

  Arm32 specific
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/dty00
/dev/dty01
/dev/dty02
/dev/tty00
/dev/tty01
/dev/tty02

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
acpi(4), ast(4), cardbus(4), isa(4), isapnp(4), mca(4), mhzc(4), ofisa(4), pcmcia(4), pcmcom(4), pnpbios(4), puc(4), rtfps(4), tty(4)

HISTORY
The com driver was originally derived from the HP9000/300 dca driver.

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.