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cytune — tune driver parameters for Cyclades-Z multiport serial card
cytune [options] tty [ ...
]
cytune queries and modifies the interruption threshold for the Cyclades driver. Each serial line on a Cyclades card has a 12-byte FIFO for input (and another 12-byte FIFO for output). The "threshold" specifies how many input characters must be present in the FIFO before an interruption is raised. When a Cyclades tty is opened, this threshold is set to a default value based on baud rate:
Baud Threshold 50-4800 10 9600 8 19200 4 38400 2 57600-150000 1
If the threshold is set too low, the large number of interruptions can load the machine and decrease overall system throughput. If the threshold is set too high, the FIFO buffer can overflow, and characters will be lost. Slower machines, however, may not be able to deal with the interrupt load, and will require that the threshold be adjusted upwards.
If the cyclades driver was compiled with ENABLE_MONITORING defined, the cytune
command can be used with the −q option to report interrupts over the
monitoring interval and characters transferred over the
monitoring interval. It will also report the state of the
FIFO. The maximum number of characters in the FIFO when an
interrupt occurred, the instantaneous count of characters in
the FIFO, and how many characters are now in the FIFO are
reported. This output might look like this:
/dev/cubC0: 830 ints, 9130 chars; fifo: 11 threshold, 11 max, 11 now
166.259866 interrupts/second, 1828.858521 characters/second
This output indicates that for this monitoring period, the
interrupts were always being handled within one character
time, because max
never rose above threshold. This is good, and
you can probably run this way, provided that a large number
of samples come out this way. You will lose characters if you
overrun the FIFO, as the Cyclades hardware does not seem to
support the RTS RS-232 signal line for hardware flow control
from the DCE to the DTE.
In query mode cytune will produce a summary report when ended with a SIGINT or when the threshold or timeout is changed.
There may be a responsiveness vs. throughput tradeoff. The
Cyclades card, at the higher speeds, is capable of putting a
very high interrupt load on the system. This will reduce the
amount of CPU time available for other tasks on your system.
However, the time it takes to respond to a single character
may be increased if you increase the threshold. This might be
noticed by monitoring ping(8) times on a SLIP link
controlled by a Cyclades card. If your SLIP link is generally
used for interactive work such as telnet(1), you may want to
leave the threshold low, so that characters are responded to
as quickly as possible. If your SLIP link is generally used
for file transfer, WWW, and the like, setting the FIFO to a
high value is likely to reduce the load on your system while
not significantly affecting throughput. Alternatively, see
the −t or −T options to adjust the time that the
cyclades waits before flushing its buffer. Units are 5ms.
If you are running a mouse on a Cyclades port, it is likely that you would want to maintain the threshold and timeout at a low value.
−s, −−set−threshold
valueSet the current threshold to value characters.
Note that if the tty is not being held
open by another process, the threshold will be reset on
the next open. Only values between 1 and 12, inclusive,
are permitted.
−t, −−set−flush
valueSet the current flush timeout to value units. Note
that if the tty
is not being held open by another process, the
threshold will be reset on the next open. Only values
between 0 and 255, inclusive, are permitted. Setting
value to
zero forces the default, currently 0x20 (160ms), but
soon to be 0x02 (10ms). Units are 5 ms.
−g, −−get−thresholdGet the current threshold and timeout.
−S, −−set−default−threshold
valueSet the default threshold to value characters.
When the tty is
next opened, this value will be used instead of the
default. Only values between 1 and 12, inclusive, are
permitted.
−T, −−set−default−flush
valueSet the default flush timeout to value units. When the
tty is next
opened, this value will be used instead of the default.
If value
is zero, then the value will default to 0x20 (160ms),
soon to be 0x02 (10ms).
−G, −−get−glushGet the default threshold and flush timeout values.
−q, −−statsGather statistics about the tty. The results are only
valid if the Cyclades driver has been compiled with
ENABLE_MONITORING
defined. This is probably not the default.
−i, −−interval intervalStatistics will be gathered every interval seconds.
If you run two copies of cytune at the same time to report statistics about the same port, the 'ints', 'chars', and 'max' value will be reset and not reported correctly. cytune should prevent this, but does not.
The cytune command is part of the util-linux package and is available from Linux Kernel Archive
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cytune.8 -- Created: Sat Mar 4 17:44:53 1995 by faithcs.unc.edu Update: Sat Mar 4 18:22:24 1995 by faithcs.unc.edu Update: Sun Mar 5 06:40:12 1995 by njsscifi.emi.net Copyright 1995 Rickard E. Faith (faithcs.unc.edu) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. " |