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NAME
sio — fast interrupt driven asynchronous serial communications interface
SYNOPSIS
For standard ISA ports:
device sio
In /boot/device.hints:
hint.sio.0.at="isa"
hint.sio.0.port="0x3f8"
hint.sio.0.flags="0x10"
hint.sio.0.irq="4"
hint.sio.1.at="isa"
hint.sio.1.port="0x2f8"
hint.sio.1.flags="0x0"
hint.sio.1.irq="3"
For AST compatible multiport cards with 4 ports:
options COM_MULTIPORT
device sio
In /boot/device.hints:
hint.sio.4.at="isa"
hint.sio.4.port="0x2a0"
hint.sio.4.flags="0x701"
hint.sio.5.at="isa"
hint.sio.5.port="0x2a8"
hint.sio.5.flags="0x701"
hint.sio.6.at="isa"
hint.sio.6.port="0x2b0"
hint.sio.6.flags="0x701"
hint.sio.7.at="isa"
hint.sio.7.port="0x2b8"
hint.sio.7.flags="0x701"
hint.sio.7.irq="12"
For Boca Board compatible multiport cards with 8 ports:
options COM_MULTIPORT
device sio
In /boot/device.hints:
hint.sio.4.at="isa"
hint.sio.4.port="0x100"
hint.sio.4.flags="0xb05"
...
hint.sio.11.at="isa"
hint.sio.11.port="0x138"
hint.sio.11.flags="0xb05"
hint.sio.11.irq="12"
For Netmos Nm9845 multiport cards with 6 ports:
options COM_MULTIPORT
device sio
In /boot/device.hints:
hint.sio.4.at="isa"
hint.sio.4.port="0xb000"
hint.sio.4.flags="0x901"
hint.sio.5.at="isa"
hint.sio.5.port="0xb400"
hint.sio.5.flags="0x901"
hint.sio.6.at="isa"
hint.sio.6.port="0xb800"
hint.sio.6.flags="0x901"
hint.sio.7.at="isa"
hint.sio.7.port="0xbc00"
hint.sio.7.flags="0x901"
hint.sio.8.at="isa"
hint.sio.8.port="0xc000"
hint.sio.8.flags="0x901"
hint.sio.9.at="isa"
hint.sio.9.port="0xac00"
hint.sio.9.flags="0x901"
hint.sio.9.irq="12"
For Hayes ESP cards:
options COM_ESP
device sio
...
For single port PCI and PCCARD cards:
device sio
No lines are required in /boot/device.hints for these cards.
For dual port PCI cards that share an interrupt:
device sio
options COM_MULTIPORT
In /boot/device.hints:
hint.sio.2.flags="0x201"
hint.sio.3.flags="0x201"
Meaning of flags:
0x00001 shared IRQs
0x00002 disable FIFO
0x00004 no AST/4 compatible IRQ control register
0x00008 recover sooner from lost output interrupts
0x00010 device is potential system console
0x00020 device is forced to become system console
0x00040 device is reserved for low-level IO (e.g. for remote kernel debugging)
0x00080 use this port for remote kernel debugging
0x0??00 minor number of master port
0x10000 PPS timestamping on CTS instead of DCD
0x20000 device is assumed to use a 16650A-type (extended FIFO) chip
DESCRIPTION
The sio driver provides support for NS8250-, NS16450-, NS16550 and NS16550A-based EIA
RS-232C (CCITT V.24) communications interfaces. The NS8250 and NS16450 have single
character buffers, the NS16550A has 16 character FIFO input and output buffers.
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, 28800, 38400, 57600, or 115200. Your
hardware may limit your baud rate choices.
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).
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 master port.
The driver supports controller based PCI modems. The 3Com FaxModem PCI and the Advantec 56k
Voice Messaging PCI FaxModem are the only cards supported. WinModems, softmodems, hfc
modems and any other modems that are not controller based are not supported.
The flags keyword may be used on each 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.
The flags keyword 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 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.
The 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.
In the synopsis, 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.
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.
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.
Serial ports controlled by the sio 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.
The sio driver also supports an initial-state and a lock-state control device for each of
the callin and the callout "data" devices. 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 stty(1) in the normal way on the initial-state devices to program
initial termios states suitable for your setup.
The lock termios state acts as flags to disable changing the termios state. E.g., to lock a
flag variable such as CRTSCTS, use 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. E.g., to lock a speed to 115200, use “stty 115200” on the initial-
state device and “stty 1” on the lock-state device.
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 do not support it at
all. CLOCAL should be locked on for devices that do not support carrier. HUPCL may be
locked off if you do not 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.
FILES
/dev/ttyd? for callin ports
/dev/ttyd?.init
/dev/ttyd?.lock corresponding callin initial-state and lock-state devices
/dev/cuad? for callout ports
/dev/cuad?.init
/dev/cuad?.lock corresponding callout initial-state and lock-state devices
/etc/rc.d/serial examples of setting the initial-state and lock-state devices
The device numbers are made from the set [0-9a-v] so that more than 10 ports can be
supported.
DIAGNOSTICS
sio%d: silo overflow. Problem in the interrupt handler.
sio%d: interrupt-level buffer overflow. Problem in the bottom half of the driver.
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.
SEE ALSO
stty(1), termios(4), tty(4), comcontrol(8)
HISTORY
The sio driver is derived from the HP9000/300 dca(4) driver and is currently under
development.
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.
Stay away from plain NS16550's. These are early implementations of the chip with non-
functional FIFO hardware.
The constants which define the locations of the various serial ports are holdovers from DOS.
As shown, hex addresses can be and for clarity probably should be used instead.
Note that on the AST/4 the card's dipswitches should not be set to use interrupt sharing.
AST/4-like interrupt sharing is only used when multiple AST/4 cards are installed in the
same system. The sio driver does not support more than 1 AST/4 on one IRQ.
The examples in the synopsis are too vendor-specific.