COM(4)                  NetBSD Kernel Interfaces 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 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), 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. NetBSD 7.1.2 April 29, 2012 NetBSD 7.1.2

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