COM(4) | Device Drivers Manual | COM(4)

# NAME

`com` —
serial communications interface for RS-232C

# 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 ?`
`com* at xirc?`
`options COM_HAYESP`
`options PPS_SYNC`
`options PPS_TRAILING_EDGE`
`options RND_COM`

## Amiga

`com* at clockport?`

## Arm32

`com0 at mainbus? base 0x00210fe0`
`com1 at mainbus? base 0x00210be0`
`com0 at pxaip?`

## HP 9000/300 and 400 Series

`com* at dio? scode ?`
`com* at frodo? offset ?`

## HP 9000/700 and 800 Series

`com* at dino?`
`com* at gsc?`
`com* at ssio?`

## IBM PowerPC 4xx

`com* at opb?`

## SPARC

`com* at ebus?`
`com* at obio0`

## x68k

`com0 at intio0 addr 0xefff00 intr 240`
`com1 at intio0 addr 0xefff10 intr 241`

# 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).)

`options COM_HAYESP` adds support for the Hayes ESP serial board.

`options PPS_SYNC` enables code to use the Data Carrier Detect (DCD) signal line for attachment to an external precision clock source (e.g., GPS, CDMA) which generates a Pulse Per Second (PPS) signal. This is used by ntpd(8) to discipline the system clock, and more accurately count/measure time. See options(4) for more discussion.

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), i386/pnpbios(4), isa(4), isapnp(4), mca(4), mhzc(4), ofisa(4), options(4), pcmcia(4), pcmcom(4), puc(4), pxaip(4), rtfps(4), tty(4), xirc(4), ntpd(8)

# 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.

March 4, 2017 | NetBSD 9.5