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 DTE (e.g., 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
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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 xhflag; /* hardware flow control
modes */
unsigned short xcflag; /* clock modes */
unsigned short xrflag[NFF];/* reserved modes */
unsigned short xsflag; /* spare local modes */
};
The xhflag 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.
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
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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 (e.g., computer) is configured as a DTE. If the connected device
(e.g., 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.
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 xcflag
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 xcflag field and
enabled at the remote connected device.
The xcflag field specifies the system treatment of clock modes.
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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.
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.
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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 =
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 xrflag is reserved for future interface definitions and should
not be used by any implementations. The xsflag 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 (fildes, command, arg)
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.
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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.
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/*
SEE ALSO
stty(1), ioctl(2), termio(7).
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