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SETSERIAL(8)		    System Manager's Manual		  SETSERIAL(8)



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 nonstadard configuration, the setserial  program  should  be
       used.   Typically  it is called from an rc.serial script, which is usu-
       ally run out of /etc/rc.local.

       The device argument or arguments	 specifies  the	 serial	 device	 which
       should be configured or interrogated.  It will usually have the follow-
       ing form: /dev/cua[0-3].

       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 configu-
       ration 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 argu-
	      ments.

       -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 preceeded 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  dis-
	      able 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 com-
	      patible UART with a 1k receive buffer to prevent receiver	 over-
	      runs.   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 parame-
	      ter,  you will see dropped characters during file transmissions.
	      These UART's usually have other problems: the skip_test  parame-
	      ter 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 fea-
	      ture 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 cheasy 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  fre-
	      quency  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 divison.  This divisor will be  used
	      then  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  dial in 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 dial in line.	 This allows the getty
	      to reset the modem (which may have had its  configuration	 modi-
	      fied  by the application using the callout device) before block-
	      ing on the open again.

       ^hup_notify
	      Do not notify a process blocked on opening a dial in  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 dis-
	      cpline  to minimize overhead.)  This is off by default, but cer-
	      tain 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 particu-
       lar 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 prob-
       ably 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 (Auxillary 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  sup-
       ports these ports, you should make use of them to avoid potential lock-
       ups 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  reg-
       ister 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 speci-
       fied 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  perfor-
	      mance;  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/rc.local /etc/rc.serial

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	(john-
       sonm@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 respon-
       sibility.



Setserial 2.17			 January 2000			  SETSERIAL(8)