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

     sio - fast interrupt driven asynchronous serial communications interface

     For standard ISA ports:
           device sio

           In /boot/device.hints:

     For AST compatible multiport cards with 4 ports:
           options COM_MULTIPORT
           device sio

           In /boot/device.hints:

     For Boca Board compatible multiport cards with 8 ports:
           options COM_MULTIPORT
           device sio

           In /boot/device.hints:

     For Netmos Nm9845 multiport cards with 6 ports:
           options COM_MULTIPORT
           device sio

           In /boot/device.hints:

     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:

     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)

     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

     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.

     /dev/ttyd?       for callin ports
     /dev/ttyd?.lock  corresponding callin initial-state and lock-state

     /dev/cuad?       for callout ports
     /dev/cuad?.lock  corresponding callout initial-state and lock-state

     /etc/rc.d/serial  examples of setting the initial-state and lock-state

     The device numbers are made from the set [0-9a-v] so that more than 10
     ports can be supported.

     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

     stty(1), termios(4), tty(4), comcontrol(8)

     The sio driver is derived from the HP9000/300 dca(4) driver and is
     currently under development.

     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.

FreeBSD 11.1-RELEASE-p4         August 30, 2006        FreeBSD 11.1-RELEASE-p4
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