TERMIOX(4I) Ioctl Requests TERMIOX(4I)

NAME

termiox - extended general terminal interface

DESCRIPTION

The extended general terminal interface supplements the termio(4I)
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 <sys/termiox.h> for your system to find out which capabilities are
supported.

Hardware Flow Control Modes

Hardware flow control supplements the termio(4I) 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 unidirectional 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 interface allows both
unidirectional and bidirectional hardware flow control; when
bidirectional 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
(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 signals to one another. 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 CITT 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. 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.

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(4I) HUPCL and the termiox DTRXOFF
bits, which use the DTE ready line for different functions.

Variations of different hardware flow control methods may be selected
by setting the appropriate bits. For example, bidirectional RTS/CTS
flow control is selected by setting both the RTSXOFF and CTSXON bits
and bidirectional DTR/CTS flow control is selected by setting both the
DTRXOFF and CTSXON. Modem control or unidirectional 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 using 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 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.4
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 0000000 TSET clock not provided.
TSETCRBRG 0000100 Output receive baud rate generator on circuit
113.
TSETCTBRG 0000200 Output transmit baud rate generator on circuit
113
TSETCTSET 0000300 Output transmitter signal element timing (DCE
source) on circuit 113.
TSETCRSET 0000400 Output 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 0000000 RSET clock not provided.
RSETCRBRG 0001000 Output receive baud rate generator on circuit
128.
RSETCTBRG 0002000 Output transmit baud rate generator on circuit
128.
RSETCTSET 0003000 Output transmitter signal element timing (DCE
source) on circuit 128.
RSETCRSET 0004000 Output 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 = 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 ioctl system calls.

IOCTLS

The ioctl(2) system calls have the form:

struct termiox *arg;
ioctl(fildes, command, 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.

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(4I)

NOTES

The termiox(4I) system call is provided for compatibility with previous
releases and its use is discouraged. Instead, the termio(4I) system
call is recommended. See termio(4I) for usage information.

illumos October 29, 2017 illumos