termiox(7) termiox(7)
NAME
termiox - extended general terminal interface
DESCRIPTION
The extended general terminal interface supplements the
termio(7) general terminal interface by adding support for
asynchronous hardware flow control, isochronous flow control
and clock modes, and local implementations of additional
asynchronous features. Some systems may not support all of
these capabilities because of either hardware or software
limitations. Other systems may not permit certain functions
to be disabled. In these cases the appropriate bits will be
ignored. See termiox.h for your system to find out which
capabilities are supported.
Hardware Flow Control Modes
Hardware flow control supplements the termio(7) IXON, IXOFF,
and IXANY character flow control. Character flow control
occurs when one device controls the data transfer of another
device by the insertion of control characters in the data
stream between devices. Hardware flow control occurs when one
device controls the data transfer of another device using
electrical control signals on wires (circuits) of the
asynchronous interface. Isochronous hardware flow control
occurs when one device controls the data transfer of another
device by asserting or removing the transmit clock signals of
that device. Character flow control and hardware flow control
may be simultaneously set.
In asynchronous, full duplex applications, the use of the
Electronic Industries Association's EIA-232-D Request To Send
(RTS) and Clear To Send (CTS) circuits is the preferred method
of hardware flow control. An interface to other hardware flow
control methods is included to provide a standard interface to
these existing methods.
The EIA-232-D standard specified only uni-directional hardware
flow control - the Data Circuit-terminating Equipment or Data
Communications Equipment (DCE) indicates to the Data Terminal
Equipment (DTE) to stop transmitting data. The termiox(7)
interface allows both uni-directional and bi-directional
hardware flow control; when bi-directional flow control is
enabled, either the DCE or DTE can indicate to each other to
stop transmitting data across the interface. Note: It is
assumed that the asynchronous port is configured as a DTE. If
the connected device is also a DTE and not a DCE, then DTE to
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DTE (for example, terminal or printer connected to computer)
hardware flow control is possible by using a null modem to
interconnect the appropriate data and control circuits.
Clock Modes
Isochronous communication is a variation of asynchronous
communication whereby two communicating devices may provide
transmit and/or receive clock to each other. Incoming clock
signals can be taken from the baud rate generator on the local
isochronous port controller, from CCITT V.24 circuit 114,
Transmitter Signal Element Timing - DCE source (EIA-232-D pin
15), or from CCITT V.24 circuit 115, Receiver Signal Element
Timing - DCE source (EIA-232-D pin 17). Outgoing clock
signals can be sent on CCITT V.24 circuit 113, Transmitter
Signal Element Timing - DTE source (EIA-232-D pin 24), on
CCITT V.24 circuit 128, Receiver Signal Element Timing - DTE
source (no EIA-232-D pin), or not sent at all.
In terms of clock modes, traditional asynchronous
communication is implemented simply by using the local baud
rate generator as the incoming transmit and receive clock
source and not outputting any clock signals.
Terminal Parameters
The parameters that control the behavior of devices providing
the termiox interface are specified by the termiox structure,
defined in the sys/termiox.h header file. Several ioctl(2)
system calls that fetch or change these parameters use this
structure:
#define NFF 5
struct termiox {
unsigned short x_hflag; /* hardware flow control
modes */
unsigned short x_cflag; /* clock modes */
unsigned short x_rflag[NFF];/* reserved modes */
unsigned short x_sflag; /* spare local modes */
};
The x_hflag field describes hardware flow control modes:
RTSXOFF 0000001 Enable RTS hardware flow control on input.
CTSXON 0000002 Enable CTS hardware flow control on output.
DTRXOFF 0000004 Enable DTR hardware flow control on input.
CDXON 0000010 Enable CD hardware flow control on output.
ISXOFF 0000020 Enable isochronous hardware flow control on input.
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The EIA-232-D DTR and CD circuits are used to establish a
connection between two systems. The RTS circuit is also used
to establish a connection with a modem. Thus, both DTR and
RTS are activated when an asynchronous port is opened. If DTR
is used for hardware flow control, then RTS must be used for
connectivity. If CD is used for hardware flow control, then
CTS must be used for connectivity. Thus, RTS and DTR (or CTS
and CD) cannot both be used for hardware flow control at the
same time. Other mutual exclusions may apply, such as the
simultaneous setting of the termio(7) HUPCL and the termiox(7)
DTRXOFF bits, which use the DTE ready line for different
functions.
Variations of different hardware flow control methods may be
selected by setting the the appropriate bits. For example,
bi-directional RTS/CTS flow control is selected by setting
both the RTSXOFF and CTSXON bits and bi-directional DTR/CTS
flow control is selected by setting both the DTRXOFF and
CTSXON. Modem control or uni-directional CTS hardware flow
control is selected by setting only the CTSXON bit.
As previously mentioned, it is assumed that the local
asynchronous port (for example, computer) is configured as a
DTE. If the connected device (for example, printer) is also a
DTE, it is assumed that the device is connected to the
computer's asynchronous port via a null modem that swaps
control circuits (typically RTS and CTS). The connected DTE
drives RTS and the null modem swaps RTS and CTS so that the
remote RTS is received as CTS by the local DTE. In the case
that CTSXON is set for hardware flow control, printer's
lowering of its RTS would cause CTS seen by the computer to be
lowered. Output to the printer is suspended
until the printer's raising of its RTS, which would cause CTS
seen by the computer to be raised.
If RTSXOFF is set, the Request To Send (RTS) circuit (line)
will be raised, and if the asynchronous port needs to have its
input stopped, it will lower the Request To Send (RTS) line.
If the RTS line is lowered, it is assumed that the connected
device will stop its output until RTS is raised.
If CTSXON is set, output will occur only if the Clear To Send
(CTS) circuit (line) is raised by the connected device. If
the CTS line is lowered by the connected device, output is
suspended until CTS is raised.
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If DTRXOFF is set, the DTE Ready (DTR) circuit (line) will be
raised, and if the asynchronous port needs to have its input
stopped, it will lower the DTE Ready (DTR) line. If the DTR
line is lowered, it is assumed that the connected device will
stop its output until DTR is raised.
If CDXON is set, output will occur only if the Received Line
Signal Detector (CD) circuit (line) is raised by the connected
device. If the CD line is lowered by the connected device,
output is suspended until CD is raised.
If ISXOFF is set, and if the isochronous port needs to have
its input stopped, it will stop the outgoing clock signal. It
is assumed that the connected device is using this clock
signal to create its output. Transit and receive clock
sources are programmed using the x_cflag fields. If the port
is not programmed for external clock generation, ISXOFF is
ignored. Output isochronous flow control is supported by
appropriate clock source programming using the x_cflag field
and enabled at the remote connected device.
The x_cflag field specifies the system treatment of clock
modes.
XMTCLK 0000007 Transmit clock source:
XCIBRG 0000000 Get transmit clock from internal baud rate
generator.
XCTSET 0000001 Get transmit clock from transmitter signal
element timing (DCE source) lead, CCITT
V.24 circuit 114, EIA-232-D pin 15.
XCRSET 0000002 Get transmit clock from receiver signal
element timing (DCE source) lead, CCITT
V.24 circuit 115, EIA-232-D pin 17.
RCVCLK 0000070 Receive clock source:
RCIBRG 0000000 Get receive clock from internal baud rate
generator.
RCTSET 0000010 Get receive clock from transmitter signal
element timing (DCE source) lead, CCITT
V.24 circuit 114, EIA-232-D pin 15.
RCRSET 0000020 Get receive clock from receiver signal
element timing (DCE source) lead, CCITT
V.24 circuit 115, EIA-232-D pin 17.
TSETCLK 0000700 Transmitter signal element timing (DTE source)
lead, CCITT V.24 circuit 113, EIA-232-D
pin 24, clock source:
TSETCOFF 0000000TSET clock not provided.
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TSETCRBRG 0000100Output receive baud rate generator on
circuit 113.
TSETCTBRG 0000200Output transmit baud rate generator on
circuit 113.
TSETCTSET 0000300Output transmitter signal element timing
(DCE source) on circuit 113.
TSETCRSET 0000400Output receiver signal element timing
(DCE source) on circuit 113.
RSETCLK 0007000 Receiver signal element timing (DTE source)
lead, CCITT V.24 circuit 128, no EIA-232-D
pin, clock source:
RSETCOFF 0000000RSET clock not provided.
RSETCRBRG 0001000Output receive baud rate generator on
circuit 128.
RSETCTBRG 0002000Output transmit baud rate generator on
circuit 128.
RSETCTSET 0003000Output transmitter signal element timing
(DCE source) on circuit 128.
RSETCRSET 0004000Output receiver signal element timing
(DCE) on circuit 128.
If the XMTCLK field has a value of XCIBRG the transmit clock
is taken from the hardware internal baud rate generator, as in
normal asynchronous transmission. If XMTCLK = XCTSET the
transmit clock is taken from the Transmitter Signal Element
Timing (DCE source) circuit. If XMTCLK = XCRSET the transmit
clock is taken from the Receiver Signal Element Timing (DCE
source) circuit.
If the RCVCLK field has a value of RCIBRG the receive clock is
taken from the hardware Internal Baud Rate Generator, as in
normal asynchronous transmission. If RCVCLK = RCTSET the
receive clock is taken from the Transmitter Signal Element
Timing (DCE source) circuit. If RCVCLK = RCRSET the receive
clock is taken from the Receiver Signal Element Timing (DCE
source) circuit.
If the TSETCLK field has a value of TSETCOFF the Transmitter
Signal Element Timing (DTE source) circuit is not driven. If
TSETCLK = TSETCRBRG the Transmitter Signal Element Timing (DTE
source) circuit is driven by the Receive Baud Rate Generator.
If TSETCLK = TSETCTBRG the Transmitter Signal Element Timing
(DTE source) circuit is driven by the Transmit Baud Rate
Generator. If TSETCLK = TSETCTSET the Transmitter Signal
Element Timing (DTE source) circuit is driven by the
Transmitter Signal Element Timing (DCE source). If TSETCLK =
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TSETCRBRG the Transmitter Signal Element Timing (DTE source)
circuit is driven by the Receiver Signal Element Timing (DCE
source).
If the RSETCLK field has a value of RSETCOFF the Receiver
Signal Element Timing (DTE source) circuit is not driven. If
RSETCLK = RSETCRBRG the Receiver Signal Element Timing (DTE
source) circuit is driven by the Receive Baud Rate Generator.
If RSETCLK = RSETCTBRG the Receiver Signal Element Timing (DTE
source) circuit is driven by the Transmit Baud Rate Generator.
If RSETCLK = RSETCTSET the Receiver Signal Element Timing (DTE
source) circuit is driven by the Transmitter Signal Element
Timing (DCE source). If RSETCLK = RSETCRBRG the Receiver
Signal Element Timing (DTE source) circuit is driven by the
Receiver Signal Element Timing (DCE source).
The x_rflag is reserved for future interface definitions and
should not be used by any implementations. The x_sflag may be
used by local implementations wishing to customize their
terminal interface using the termiox(7) ioctl system calls.
ioctls
The ioctl(2) system calls have the form:
ioctl (int fildes, int command, struct termiox *arg);
The commands using this form are:
TCGETX
The argument is a pointer to a termiox structure. The
current terminal parameters are fetched and stored into
that structure.
TCSETX
The argument is a pointer to a termiox structure. The
current terminal parameters are set from the values
stored in that structure. The change is immediate.
TCSETXW
The argument is a pointer to a termiox structure. The
current terminal parameters are set from the values
stored in that structure. The change occurs after all
characters queued for output have been transmitted.
This form should be used when changing parameters that
will affect output.
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TCSETXF
The argument is a pointer to a termiox structure. The
current terminal parameters are set from the values
stored in that structure. The change occurs after all
characters queued for output have been transmitted; all
characters queued for input are discarded and then the
change occurs.
FILES
/dev/*
REFERENCES
ioctl(2), stty(1), termio(7)
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