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SIO(4)                 FreeBSD Kernel Interfaces Manual                 SIO(4)

NAME
     sio -- fast interrupt driven asynchronous serial communications interface

SYNOPSIS
     For standard ports:
     device sio0 at isa? port IO_COM1 irq 4
     device sio1 at isa? port IO_COM2 irq 3
     device sio2 at isa? port IO_COM3 irq 5
     device sio3 at isa? port IO_COM4 irq 9

     For AST compatible multiport cards with 4 ports:
     options COM_MULTIPORT
     device sio4 at isa? port 0x2a0 flags 0x701
     device sio5 at isa? port 0x2a8 flags 0x701
     device sio6 at isa? port 0x2b0 flags 0x701
     device sio7 at isa? port 0x2b8 flags 0x701 irq 12

     For Boca Board compatible multiport cards with 8 ports:
     options COM_MULTIPORT
     device sio4 at isa? port 0x100 flags 0xb05
     ...
     device sio11 at isa? port 0x138 flags 0xb05 irq 12

     For Netmos Nm9845 multiport cards with 6 ports:
     options COM_MULTIPORT
     device sio4 at isa? port 0xb000 flags 0x901
     device sio5 at isa? port 0xb400 flags 0x901
     device sio6 at isa? port 0xb800 flags 0x901
     device sio7 at isa? port 0xbc00 flags 0x901
     device sio8 at isa? port 0xc000 flags 0x901
     device sio9 at isa? port 0xac00 flags 0x901 irq 12

     For Hayes ESP cards:
     options COM_ESP
     ...

     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
           0x20000   device is assumed to use a 16650A-type (extended FIFO)
                     chip

     Minor numbering:

     0bOLIMMMMM
       callOut
        Lock
         Initial
          MMMMMinor

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,
     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.  Fre-
     quently 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 flags keyword may be used on each device sio line in the kernel con-
     figuration 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 con-
     trol 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 minor
     number of the initial-state device is 32 higher than that of the corre-
     sponding 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
     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.

     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 cer-
     tain 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/ttyid?
     /dev/ttyld?  corresponding callin initial-state and lock-state devices

     /dev/cuaa?   for callout ports
     /dev/cuaia?
     /dev/cuala?  corresponding callout initial-state and lock-state devices

     /etc/rc.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 cur-
     rently 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 can-
     not 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 prob-
     ably 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.

FreeBSD 4.10                   October 10, 1995                   FreeBSD 4.10

NAME | SYNOPSIS | DESCRIPTION | FILES | DIAGNOSTICS | SEE ALSO | HISTORY | BUGS

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