SETSERIAL

NAME

SYNOPSIS

setserial -g [ -abv ] device1 ...  

DESCRIPTION

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 usually 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 following form: /dev/cua[0-3].

If no parameters are specified, setserial will print out the port type (i.e., 8250, 16450, 16550, 16550A), 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

-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.

-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.

PARAMETERS

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, and 16550A. Since the 8250 and 16450 UARTS do not have FIFO's, and since the original 16550 have bugs which make the FIFO's unusable, the FIFO will only be used on chips identifiied as 16550A UARTs. Setting the UART type to 8250, 16450, or 16550 will enable the serial port without trying to use the FIFO. 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.

autoconfigure

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 autoconfigure parameter should be given after the port,auto_irq, andskip_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 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 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_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.

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 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 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.

CONSIDERATIONS OF CONFIGURING SERIAL PORTS

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 (Auxillary device in PS/2)
IRQ 13      Math coprocessor
IRQ 14      Hard disk controller
IRQ 15      Reserved

CAUTION

FILES

SEE ALSO

AUTHOR

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.

Index

NAME

SYNOPSIS

DESCRIPTION

OPTIONS

PARAMETERS

CONSIDERATIONS OF CONFIGURING SERIAL PORTS

CAUTION

FILES

SEE ALSO

AUTHOR