HP-UX Reference (11i v3 07/02) - 7 Device (Special) Files, 9 General Information, Index (vol 10)

t
termio(7) termio(7)
SAM or kctune(1M) may be used to change the
nclist value.
DEPENDENCIES
Workstations
Built-in serial ports on workstation machines support the following additional baud rate settings: 57600,
and 115200. An RS-232-to-RS-422 converter may be required to achieve practical cable lengths at these
baud rates (because RS-232 only specifies up to 19200 baud).
Timed delays are not supported.
Built-in serial ports on workstation systems have RTS and CTS flow control capability, configurable receive
FIFO trigger levels, and a configurable transmit limit. RTS/CTS hardware handshaking can be enabled
through a bit in the device file minor number, through an
ioctl() call (see termiox(7)), or through the
stty command (see stty(1)).
The receive FIFO trigger level is configurable through two bits in the device file minor number. The
receive FIFO trigger level is used to set the level at which a receive interrupt is generated to the system.
Setting a smaller value for the receive FIFO trigger level enables the system to react more quickly to
receipt of characters. However, using a smaller trigger level increases system overhead to process the
additional interrupts. A higher receive FIFO trigger level reduces the system interrupt overhead for heavy
inbound data traffic at the cost of less time for the system to read data from the hardware before receive
FIFOs are overrun. When using RTS flow control, the receive FIFO trigger level also determines the point
at which the hardware lowers RTS to protect the receive FIFO. Use of a higher receive FIFO trigger level
also reduces XOFF flow control responsiveness because, under light inbound data flow conditions, receipt of
the XOFF character by the system is slightly delayed. Choice of the appropriate receive FIFO trigger level
should be based upon how the serial port is to be used. For most applications a receive FIFO trigger level
of 8 (c3,c2 = 10) is suggested.
Two bits in the device file minor number specify the transmit limit, the number of characters which are suc-
cessively loaded into the transmit FIFO. Setting a smaller transmit limit allows the transmitter to be more
responsive to flow control either from receipt of an XOFF character or de-assertion of CTS at the cost of
increased system interrupt overhead. Setting a larger transmit limit reduces interrupt overhead but is not
as responsive to flow control since the remainder of the transmit FIFO can be transmitted even after the
transmitter is flow controlled. When communicating with devices which have little tolerance for data
receipt after flow control, one must choose the transmit limit appropriately.
Device File Minor Number
Workstation device file minor numbers take the form:
0xIIC0HM
where:
II = Two hexadecimal digits (8 bits) to indicate the instance of the serial interface.
C = One hexadecimal digit (4 bits) for FIFO control. Values for each bit are as follows:
Receive FIFO Trigger Level Transmit Limit
c3 c2 Level c1 c0 Limit
001001
014014
108108
1 1 14 1 1 12
H = One hexadecimal digit (4 bits) which controls diagnostic access and hardware flow control.
Bit Value
h3 Diagnostic telephony access
h2 Reserved
h1 Reserved
h0 Enables RTS/CTS hardware flow control
M = One hexadecimal digit (4 bits) to determine the port access type. Values for each bit are as
follows:
HP-UX 11i Version 3: February 2007 − 19 − Hewlett-Packard Company 227