cytune - phpMan

CYTUNE(8) Linux Programmer’s Manual CYTUNE(8)

NAME
cytune - Tune Cyclades driver parameters

SYNOPSIS
cytune [-q [-i interval]] ([-s value]|[-S value]) [-g|G] ([-t timeout]|[-T time-
out]) tty [tty ...]

DESCRIPTION
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, how-
ever, 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 com-
mand can be used with the -q option to report interrupts over the monitoring inter-
val 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 inter-
rupt 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 hard-
ware 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 gen-
erally 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.

OPTIONS
-s value
Set 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 value
Set 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 the current threshold and timeout.

-T value
Set 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
the value will default to 0x20 (160ms), soon to be 0x02 (10ms).

-G Get the default threshold and flush timeout values.

-q Gather 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
Statistics will be gathered every interval seconds.

BUGS
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 cor-
rectly. cytune should prevent this, but does not.

FILES
/dev/ttyC[0-8]
/dev/cubC[0-8]