COM(4) BSD Kernel Interfaces Manual COM(4)NAMEcom — 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
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 ?
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
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 ALSOacpi(4), ast(4), cardbus(4), isa(4), isapnp(4), mca(4), mhzc(4),
ofisa(4), options(4), pcmcia(4), pcmcom(4), pnpbios(4), puc(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.
BSD June 7, 2011 BSD
