Provided by: setserial_2.17-51_amd64 bug

NAME

       setserial - get/set Linux serial port information

SYNOPSIS

       setserial [ -abqvVWz ] device [ parameter1 [ arg ] ] ...

       setserial -g [ -abGv ] device1 ...

DESCRIPTION

       setserial  is  a  program  designed  to  set  and/or  report the configuration information
       associated with a serial port.   This  information  includes  what  I/O  port  and  IRQ  a
       particular serial port is using, and whether or not the break key should be interpreted as
       the Secure Attention Key, and so on.

       During the normal bootup process, only COM ports 1-4 are initialized,  using  the  default
       I/O  ports  and IRQ values, as listed below.  In order to initialize any additional serial
       ports, or to change the COM 1-4  ports  to  a  nonstandard  configuration,  the  setserial
       program should be used.  Typically it is called from an setserial script, which is usually
       run out of /etc/init.d.

       The device argument specifies which device to  configure  or  to  interrogate.   Examples:
       /dev/ttyS0, /dev/ttyS1, /dev/ttyS2, /dev/ttyS3, etc.

       If no parameters are specified, setserial will print out the port type (i.e., 8250, 16450,
       16550, 16550A, etc.), the hardware I/O port, the hardware IRQ line, its "baud  base,"  and
       some of its operational flags.

       If the -g option is given, the arguments to setserial are interpreted as a list of devices
       for which the characteristics of those devices should be printed.

       Without the -g option, the first argument to setserial is interpreted as the device to  be
       modified or characteristics to be printed, and any additional arguments are interpreted as
       parameters which should be assigned to that serial device.

       For the most part, superuser privilege is required to set the configuration parameters  of
       a  serial  port.   A  few  serial port parameters can be set by normal users, however, and
       these will be noted as exceptions in this manual page.

OPTIONS

       Setserial accepts the following options:

       -a     When  reporting  the  configuration  of  a  serial  device,  print  all   available
              information.

       -b     When  reporting  the  configuration  of  a  serial  device,  print a summary of the
              device's configuration, which might be suitable  for  printing  during  the  bootup
              process, during the /etc/rc script.

       -G     Print  out  the configuration information of the serial port in a form which can be
              fed back to setserial as command-line arguments.

       -q     Be quiet.  Setserial will print fewer lines of output.

       -v     Be verbose.  Setserial will print additional status output.

       -V     Display version and exit.

       -W     Do wild interrupt initialization and exit.  This option is no  longer  relevant  in
              Linux kernels after version 2.1.

       -z     Zero  out  the  serial  flags before starting to set flags.  This is related to the
              automatic saving of serial flags using the -G flag.

PARAMETERS

       The following parameters can be assigned to a serial port.

       All argument values are assumed to be in decimal unless preceded by "0x".

       port port_number
              The port option sets the I/O port, as described above.

       irq irq_number
              The irq option sets the hardware IRQ, as described above.

       uart uart_type
              This option is used to set the UART type.  The  permitted  types  are  none,  8250,
              16450, 16550, 16550A, 16650, 16650V2, 16654, 16750, 16850, 16950, and 16954.  Using
              UART type none will disable the port.

              Some internal modems are billed as having a "16550A UART with a 1k  buffer".   This
              is a lie.  They do not have really have a 16550A compatible UART; instead what they
              have is a 16450 compatible UART with  a  1k  receive  buffer  to  prevent  receiver
              overruns.   This  is  important,  because they do not have a transmit FIFO.  Hence,
              they are not compatible with a 16550A UART, and the autoconfiguration process  will
              correctly identify them as 16450's.  If you attempt to override this using the uart
              parameter, you will see dropped characters during file transmissions.  These UART's
              usually have other problems: the skip_test parameter also often must be specified.

       autoconfig
              When  this  parameter  is  given,  setserial  will  ask  the  kernel  to attempt to
              automatically configure the serial port.  The I/O port must be correctly  set;  the
              kernel  will  attempt  to determine the UART type, and if the auto_irq parameter is
              set, Linux will  attempt  to  automatically  determine  the  IRQ.   The  autoconfig
              parameter  should  be  given after the port,auto_irq, and skip_test parameters have
              been specified.

       auto_irq
              During autoconfiguration, try to determine the IRQ.  This feature is not guaranteed
              to  always  produce  the correct result; some hardware configurations will fool the
              Linux kernel.  It is generally safer not to use the auto_irq feature, but rather to
              specify the IRQ to be used explicitly, using the irq parameter.

       ^auto_irq
              During autoconfiguration, do not try to determine the IRQ.

       skip_test
              During  autoconfiguration,  skip  the  UART test.  Some internal modems do not have
              National Semiconductor compatible UART's, but have cheap imitations instead.   Some
              of these cheesy imitations UART's do not fully support the loopback detection mode,
              which is used by the kernel to make sure there really is a  UART  at  a  particular
              address before attempting to configure it.  So for certain internal modems you will
              need to specify this parameter so Linux can initialize the UART correctly.

       ^skip_test
              During autoconfiguration, do not skip the UART test.

       baud_base baud_base
              This option sets the base baud rate, which is the clock frequency  divided  by  16.
              Normally  this  value is 115200, which is also the fastest baud rate which the UART
              can support.

       spd_hi Use 57.6kb when the application requests 38.4kb.  This parameter may  be  specified
              by a non-privileged user.

       spd_vhi
              Use 115kb when the application requests 38.4kb.  This parameter may be specified by
              a non-privileged user.

       spd_shi
              Use 230kb when the application requests 38.4kb.  This parameter may be specified by
              a non-privileged user.

       spd_warp
              Use 460kb when the application requests 38.4kb.  This parameter may be specified by
              a non-privileged user.

       spd_cust
              Use the custom divisor to set the speed when the application requests  38.4kb.   In
              this  case,  the baud rate is the baud_base divided by the divisor.  This parameter
              may be specified by a non-privileged user.

       spd_normal
              Use 38.4kb when the application requests 38.4kb.  This parameter may  be  specified
              by a non-privileged user.

       divisor divisor
              This  option  sets the custom divisor.  This divisor will be used when the spd_cust
              option is selected and the serial port is set to 38.4kb by the  application.   This
              parameter may be specified by a non-privileged user.

       sak    Set the break key at the Secure Attention Key.

       ^sak   disable the Secure Attention Key.

       fourport
              Configure the port as an AST Fourport card.

       ^fourport
              Disable AST Fourport configuration.

       close_delay delay
              Specify  the  amount of time, in hundredths of a second, that DTR should remain low
              on a serial line after the callout device is  closed,  before  the  blocked  dialin
              device  raises DTR again.  The default value of this option is 50, or a half-second
              delay.

       closing_wait delay
              Specify the amount of time, in hundredths of a second, that the kernel should  wait
              for  data to be transmitted from the serial port while closing the port.  If "none"
              is specified, no delay will occur. If "infinite" is specified the kernel will  wait
              indefinitely  for the buffered data to be transmitted.  The default setting is 3000
              or 30 seconds of delay.  This default is generally appropriate  for  most  devices.
              If  too  long a delay is selected, then the serial port may hang for a long time if
              when a serial port which is not connected, and has data pending, is closed.  If too
              short  a  delay is selected, then there is a risk that some of the transmitted data
              is output  at  all.   If  the  device  is  extremely  slow,  like  a  plotter,  the
              closing_wait may need to be larger.

       session_lockout
              Lock  out  callout  port (/dev/cuaXX) accesses across different sessions.  That is,
              once a process has opened a port, do not allow a process with a  different  session
              ID to open that port until the first process has closed it.

       ^session_lockout
              Do not lock out callout port accesses across different sessions.

       pgrp_lockout
              Lock  out callout port (/dev/cuaXX) accesses across different process groups.  That
              is, once a process has opened a port, do not allow a process in a different process
              group to open that port until the first process has closed it.

       ^pgrp_lockout
              Do not lock out callout port accesses across different process groups.

       hup_notify
              Notify a process blocked on opening a dialin line when a process has finished using
              a callout line (either by closing it or by  the  serial  line  being  hung  up)  by
              returning EAGAIN to the open.

              The  application  of  this  parameter  is for getty's which are blocked on a serial
              port's dialin line.  This allows the getty to reset the modem (which may  have  had
              its  configuration  modified  by  the  application using the callout device) before
              blocking on the open again.

       ^hup_notify
              Do not notify a process blocked on opening a dialin line when the callout device is
              hung up.

       split_termios
              Treat the termios settings used by the callout device and the termios settings used
              by the dialin devices as separate.

       ^split_termios
              Use the same termios structure to store both the dialin and callout ports.  This is
              the default option.

       callout_nohup
              If this particular serial port is opened as a callout device, do not hangup the tty
              when carrier detect is dropped.

       ^callout_nohup
              Do not skip hanging up the tty when a serial port is opened as  a  callout  device.
              Of course, the HUPCL termios flag must be enabled if the hangup is to occur.

       low_latency
              Minimize  the  receive  latency  of  the  serial  device at the cost of greater CPU
              utilization.  (Normally there is an average of 5-10ms latency before characters are
              handed  off  to the line discipline to minimize overhead.)  This is off by default,
              but certain real-time applications may find this useful.

       ^low_latency
              Optimize for efficient CPU processing of serial characters at the cost of paying an
              average  of  5-10ms  of  latency  before the characters are processed.  This is the
              default.

CONSIDERATIONS OF CONFIGURING SERIAL PORTS

       It is important to note that setserial merely tells  the  Linux  kernel  where  it  should
       expect  to  find  the  I/O  port and IRQ lines of a particular serial port.  It does *not*
       configure the hardware, the actual serial board, to use a particular I/O port.   In  order
       to  do that, you will need to physically program the serial board, usually by setting some
       jumpers or by switching some DIP switches.

       This section will provide some pointers in helping  you  decide  how  you  would  like  to
       configure your serial ports.

       The "standard MS-DOS" port associations are given below:

              /dev/ttyS0 (COM1), port 0x3f8, irq 4
              /dev/ttyS1 (COM2), port 0x2f8, irq 3
              /dev/ttyS2 (COM3), port 0x3e8, irq 4
              /dev/ttyS3 (COM4), port 0x2e8, irq 3

       Due  to the limitations in the design of the AT/ISA bus architecture, normally an IRQ line
       may not be shared between two or more serial ports.  If you attempt to  do  this,  one  or
       both  serial  ports  will  become  unreliable if you try to use both simultaneously.  This
       limitation can be overcome by special multi-port serial port boards, which are designed to
       share  multiple serial ports over a single IRQ line.  Multi-port serial cards supported by
       Linux include the AST FourPort, the Accent Async board, the Usenet Serial  II  board,  the
       Bocaboard BB-1004, BB-1008, and BB-2016 boards, and the HUB-6 serial board.

       The  selection  of  an  alternative  IRQ line is difficult, since most of them are already
       used.  The following table lists the "standard MS-DOS" assignments of available IRQ lines:

              IRQ 3: COM2
              IRQ 4: COM1
              IRQ 5: LPT2
              IRQ 7: LPT1

       Most people find that IRQ 5 is a good choice, assuming that there  is  only  one  parallel
       port  active in the computer.  Another good choice is IRQ 2 (aka IRQ 9); although this IRQ
       is sometimes used by network cards, and very rarely VGA cards will be  configured  to  use
       IRQ  2  as  a vertical retrace interrupt.  If your VGA card is configured this way; try to
       disable it so you can reclaim that IRQ line for some other card.  It's not  necessary  for
       Linux and most other Operating systems.

       The  only  other  available  IRQ lines are 3, 4, and 7, and these are probably used by the
       other serial and parallel ports.  (If your serial card has a 16bit  card  edge  connector,
       and supports higher interrupt numbers, then IRQ 10, 11, 12, and 15 are also available.)

       On AT class machines, IRQ 2 is seen as IRQ 9, and Linux will interpret it in this manner.

       IRQ's other than 2 (9), 3, 4, 5, 7, 10, 11, 12, and 15, should not be used, since they are
       assigned to other hardware and cannot, in general, be changed.  Here  are  the  "standard"
       assignments:

              IRQ  0      Timer channel 0
              IRQ  1      Keyboard
              IRQ  2      Cascade for controller 2
              IRQ  3      Serial port 2
              IRQ  4      Serial port 1
              IRQ  5      Parallel port 2 (Reserved in PS/2)
              IRQ  6      Floppy diskette
              IRQ  7      Parallel port 1
              IRQ  8      Real-time clock
              IRQ  9      Redirected to IRQ2
              IRQ 10      Reserved
              IRQ 11      Reserved
              IRQ 12      Reserved (Auxiliary device in PS/2)
              IRQ 13      Math coprocessor
              IRQ 14      Hard disk controller
              IRQ 15      Reserved

MULTIPORT CONFIGURATION

       Certain multiport serial boards which share multiple ports on a single IRQ use one or more
       ports to indicate whether or not there are any pending ports which need  to  be  serviced.
       If  your  multiport  board  supports  these  ports,  you  should make use of them to avoid
       potential lockups if the interrupt gets lost.

       In order to set these ports specify set_multiport as a parameter, and follow it  with  the
       multiport  parameters.  The multiport parameters take the form of specifying the port that
       should be checked, a mask which indicate which bits in the register are  significant,  and
       finally, a match parameter which specifies what the significant bits in that register must
       match when there is no more pending work to be done.

       Up  to  four  such  port/mask/match  combinations  may  be  specified.   The  first   such
       combinations  should be specified by setting the parameters port1, mask1, and match1.  The
       second such combination should be specified with port2, mask2, and match2, and so on.   In
       order to disable this multiport checking, set port1 to be zero.

       In  order  to  view the current multiport settings, specify the parameter get_multiport on
       the command line.

       Here are some multiport settings for some common serial boards:

              AST FourPort    port1 0x1BF mask1 0xf match1 0xf

              Boca BB-1004/8  port1 0x107 mask1 0xff match1 0

              Boca BB-2016    port1 0x107 mask1 0xff match1 0
                              port2 0x147 mask2 0xff match2 0

Hayes ESP Configuration

       Setserial may also be used to configure ports on a Hayes ESP serial board.

       The following parameters when configuring ESP ports:

       rx_trigger
              This is the trigger level (in bytes) of the receive FIFO. Larger values may  result
              in  fewer  interrupts and hence better performance; however, a value too high could
              result in data loss. Valid values are 1 through 1023.

       tx_trigger
              This is the trigger level (in bytes) of the transmit FIFO. Larger values may result
              in  fewer  interrupts and hence better performance; however, a value too high could
              result in degraded transmit performance. Valid values are 1 through 1023.

       flow_off
              This is the level (in bytes) at which the ESP  port  will  "flow  off"  the  remote
              transmitter  (i.e.  tell  him to stop stop sending more bytes).  Valid values are 1
              through 1023.  This value should be greater than the receive trigger level and  the
              flow on level.

       flow_on
              This  is  the  level  (in  bytes)  at  which the ESP port will "flow on" the remote
              transmitter (i.e. tell him to resume sending bytes) after  having  flowed  it  off.
              Valid  values  are  1  through  1023.   This value should be less than the flow off
              level, but greater than the receive trigger level.

       rx_timeout
              This is the amount of time that the ESP port will wait after  receiving  the  final
              character  before signaling an interrupt.  Valid values are 0 through 255.  A value
              too high will increase  latency,  and  a  value  too  low  will  cause  unnecessary
              interrupts.

CAUTION

       CAUTION: Configuring a serial port to use an incorrect I/O port can lock up your machine.

FILES

       /etc/serial.conf /etc/init.d/setserial

SEE ALSO

       tty(4), ttys(4), kernel/chr_drv/serial.c

AUTHOR

       The original version of setserial was written by Rick Sladkey (jrs@world.std.com), and was
       modified by Michael K. Johnson (johnsonm@stolaf.edu).

       This version has since been rewritten from scratch by  Theodore  Ts'o  (tytso@mit.edu)  on
       1/1/93.  Any bugs or problems are solely his responsibility.

       Debian   related   problems   with   this   system   should  be  sent  to  Gordon  Russell
       (gor@debian.org).