.\" Copyright (c) 1990, 1991 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" the Systems Programming Group of the University of Utah Computer
.\" Science Department.
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.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
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.\"     from: @(#)dca.4	5.2 (Berkeley) 3/27/91
.\"	from: com.4,v 1.1 1993/08/06 11:19:07 cgd Exp
.\" $FreeBSD: src/share/man/man4/sio.4,v 1.34.2.4 2002/12/18 13:31:17 keramida Exp $
.\" $DragonFly: src/share/man/man4/sio.4,v 1.2 2003/06/17 04:36:59 dillon Exp $
.\"
.Dd October 10, 1995
.Dt SIO 4
.Os
.Sh NAME
.Nm sio
.Nd "fast interrupt driven asynchronous serial communications interface"
.Sh SYNOPSIS
For standard ports:
.Cd "device sio0 at isa? port IO_COM1 irq 4"
.Cd "device sio1 at isa? port IO_COM2 irq 3"
.Cd "device sio2 at isa? port IO_COM3 irq 5"
.Cd "device sio3 at isa? port IO_COM4 irq 9"
.Pp
For AST compatible multiport cards with 4 ports:
.Cd "options COM_MULTIPORT"
.Cd "device sio4 at isa? port 0x2a0 flags 0x701"
.Cd "device sio5 at isa? port 0x2a8 flags 0x701"
.Cd "device sio6 at isa? port 0x2b0 flags 0x701"
.Cd "device sio7 at isa? port 0x2b8 flags 0x701 irq 12"
.Pp
For Boca Board compatible multiport cards with 8 ports:
.Cd "options COM_MULTIPORT"
.Cd "device sio4 at isa? port 0x100 flags 0xb05"
.Cd "..."
.Cd "device sio11 at isa? port 0x138 flags 0xb05 irq 12"
.Pp
For Netmos Nm9845 multiport cards with 6 ports:
.Cd "options COM_MULTIPORT"
.Cd "device sio4 at isa? port 0xb000 flags 0x901"
.Cd "device sio5 at isa? port 0xb400 flags 0x901"
.Cd "device sio6 at isa? port 0xb800 flags 0x901"
.Cd "device sio7 at isa? port 0xbc00 flags 0x901"
.Cd "device sio8 at isa? port 0xc000 flags 0x901"
.Cd "device sio9 at isa? port 0xac00 flags 0x901 irq 12"
.Pp
For Hayes ESP cards:
.Cd "options COM_ESP"
.Cd "..."
.Pp
Meaning of
.Ar flags :
.Bl -tag -offset indent -compact -width 0x000000
.It 0x00001
shared IRQs
.It 0x00002
disable FIFO
.It 0x00004
no AST/4 compatible IRQ control register
.It 0x00008
recover sooner from lost output interrupts
.It 0x00010
device is potential system console
.It 0x00020
device is forced to become system console
.It 0x00040
device is reserved for low-level IO (e. g. for remote kernel debugging)
.It 0x00080
use this port for remote kernel debugging
.It 0x0 Ns Em ?? Ns 00
minor number of master port
.It 0x20000
device is assumed to use a 16650A-type (extended FIFO) chip
.El
.Pp
Minor numbering:
.Bd -literal
0b\fIOLIMMMMM\fR
  call\fBO\fRut
   \fBL\fRock
    \fBI\fRnitial
     \fBMMMMM\fRinor
.Ed
.Sh DESCRIPTION
The
.Nm
driver provides support for NS8250-, NS16450-, NS16550 and NS16550A-based
.Tn EIA
.Tn RS-232C
.Pf ( Tn CCITT
.Tn V.24 )
communications interfaces.  The NS8250 and NS16450 have single character
buffers, the NS16550A has 16 character FIFO input and output buffers.
.Pp
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. Your hardware may limit your baud
rate choices.
.Pp
The driver supports `multiport' cards.
Multiport cards are those that have one or more groups of ports
that share an Interrupt Request (IRQ) line per group.
Shared IRQs on different cards are not supported.
Frequently 4 ports share 1 IRQ; some 8 port cards have 2 groups of 4 ports,
thus using 2 IRQs.
Some cards allow the first 2 serial ports to have separate IRQs per port
(as per DOS PC standard).
.Pp
Some cards have an IRQ control register for each group.
Some cards require special initialization related to such registers.
Only AST/4 compatible IRQ control registers are supported.
Some cards have an IRQ status register for each group.
The driver does not require or use such registers yet.
To work, the control and status registers for a group, if any,
must be mapped to the scratch register (register 7)
of a port in the group.
Such a port is called a
.Em master
port.
.Pp
The
.Em flags
keyword may be used on each
.Em device sio
line in the kernel configuration file
to disable the FIFO on 16550A UARTs
(see the synopsis).
Disabling the FIFO should rarely be necessary.
.Pp
The
.Em flags
keyword
.Em must
be used for all ports that are part of an IRQ sharing group.
One bit specifies IRQ sharing; another bit specifies whether the port does
.Em not
require AST/4 compatible initialization.
The minor number of the device corresponding a master port
for the group is encoded as a bitfield in the high byte.
The same master port must be specified for all ports in a group.
.Pp
The
.Em irq
specification must be given for master ports
and for ports that are not part of an IRQ sharing group,
and not for other ports.
.Pp
In the synopsis,
.Em flags 0x701
means that the 8th port (sio7) is the master
port, and that the port is on a multiport card with shared IRQs
and an AST/4 compatible IRQ control register.
.Pp
.Em flags 0xb05
means that the 12th port (sio11) is the master
port, and that the port is on a multiport card with shared IRQs
and no special IRQ control register.
.Pp
Which port is the master port depends on the card type.
Consult the hardware documentation of your card.
Since IRQ status registers are never used,
and IRQ control registers are only used for AST/4 compatible cards,
and some cards map the control/status registers to all ports in a group,
any port in a group will sometimes do for the master port.
Choose a port containing an IRQ status register for forwards compatibility,
and the highest possible port for consistency.
.Pp
Serial ports controlled by the
.Nm
driver can be used for both `callin' and `callout'.
For each port there is a callin device and a callout device.
The minor number of the callout device is 128 higher
than that of the corresponding callin port.
The callin device is general purpose.
Processes opening it normally wait for carrier
and for the callout device to become inactive.
The callout device is used to steal the port from
processes waiting for carrier on the callin device.
Processes opening it do not wait for carrier
and put any processes waiting for carrier on the callin device into
a deeper sleep so that they do not conflict with the callout session.
The callout device is abused for handling programs that are supposed
to work on general ports and need to open the port without waiting
but are too stupid to do so.
.Pp
The
.Nm
driver also supports an initial-state and a lock-state control
device for each of the callin and the callout "data" devices.
The minor number of the initial-state device is 32 higher
than that of the corresponding data device.
The minor number of the lock-state device is 64 higher
than that of the corresponding data device.
The termios settings of a data device are copied
from those of the corresponding initial-state device
on first opens and are not inherited from previous opens.
Use
.Xr stty 1
in the normal way on the initial-state devices to program
initial termios states suitable for your setup.
.Pp
The lock termios state acts as flags to disable changing
the termios state.  E.g., to lock a flag variable such as
CRTSCTS, use
.Em stty crtscts
on the lock-state device.  Speeds and special characters
may be locked by setting the corresponding value in the lock-state
device to any nonzero value.
.Pp
Correct programs talking to correctly wired external devices
work with almost arbitrary initial states and almost no locking,
but other setups may benefit from changing some of the default
initial state and locking the state.
In particular, the initial states for non (POSIX) standard flags
should be set to suit the devices attached and may need to be
locked to prevent buggy programs from changing them.
E.g., CRTSCTS should be locked on for devices that support
RTS/CTS handshaking at all times and off for devices that don't
support it at all.  CLOCAL should be locked on for devices
that don't support carrier.  HUPCL may be locked off if you don't
want to hang up for some reason.  In general, very bad things happen
if something is locked to the wrong state, and things should not
be locked for devices that support more than one setting.  The
CLOCAL flag on callin ports should be locked off for logins
to avoid certain security holes, but this needs to be done by
getty if the callin port is used for anything else.
.Sh FILES
.Bl -tag -width /dev/ttyid? -compact
.It Pa /dev/ttyd?
for callin ports
.It Pa /dev/ttyid?
.It Pa /dev/ttyld?
corresponding callin initial-state and lock-state devices
.Pp
.It Pa /dev/cuaa?
for callout ports
.It Pa /dev/cuaia?
.It Pa /dev/cuala?
corresponding callout initial-state and lock-state devices
.El
.Pp
.Bl -tag -width /etc/rc.serial -compact
.It Pa /etc/rc.serial
examples of setting the initial-state and lock-state devices
.El
.Pp
The device numbers are made from the set [0-9a-v] so that more than
10 ports can be supported.
.Sh DIAGNOSTICS
.Bl -diag
.It sio%d: silo overflow.
Problem in the interrupt handler.
.El
.Bl -diag
.It sio%d: interrupt-level buffer overflow.
Problem in the bottom half of the driver.
.El
.Bl -diag
.It sio%d: tty-level buffer overflow.
Problem in the application.
Input has arrived faster than the given module could process it
and some has been lost.
.El
.\" .Bl -diag
.\" .It sio%d: reduced fifo trigger level to %d.
.\" Attempting to avoid further silo overflows.
.\" .El
.Sh SEE ALSO
.Xr stty 1 ,
.Xr termios 4 ,
.Xr tty 4 ,
.Xr comcontrol 8
.Sh HISTORY
The
.Nm
driver is derived from the
.Tn HP9000/300
.Xr dca 4
driver and is
.Ud
.Sh BUGS
Data loss may occur at very high baud rates on slow systems,
or with too many ports on any system,
or on heavily loaded systems when crtscts cannot be used.
The use of NS16550A's reduces system load and helps to avoid data loss.
.Pp
Stay away from plain NS16550's. These are early
implementations of the chip with non-functional FIFO hardware.
.Pp
The constants which define the locations
of the various serial ports are holdovers from
.Tn DOS .
As shown, hex addresses can be and for clarity probably should be used instead.
.Pp
Note that on the AST/4 the card's dipswitches should
.Em not
be set to use interrupt sharing.
AST/4-like interrupt sharing is only used when
.Em multiple
AST/4 cards are installed in the same system.  The sio driver does not
support more than 1 AST/4 on one IRQ.
.Pp
The examples in the synopsis are too vendor-specific.