Yolinux.com

setserial manpage

Search topic Section
Get manual page for the search topic
List all commands matching the search topic
List all topics in the manpage index

SETSERIAL(8)							  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  pro-
	      cess  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)
YoLinux.com Home Page
YoLinux Tutorial Index
Privacy Policy | Advertise with us | Feedback Form |
Unauthorized copying or redistribution prohibited.
    Bookmark and Share