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RedHat 9 (Linux i386) - man page for cytune (redhat section 8)

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

       cytune - Tune Cyclades driver parameters

       cytune  [-q  [-i interval]] ([-s value]|[-S value]) [-g|G] ([-t timeout]|[-T timeout]) tty
       [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  charac-
       ters 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.   cytune will in query mode 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  possi-
       ble.   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  signifi-
       cantly  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  main-
       tain the threshold and timeout at a low value.

       -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

       -i interval
	      Statistics 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(8)
       should prevent this, but does not.

       Nick Simicich (njs@scifi.emi.net), with modifications by Rik Faith (faith@cs.unc.edu)



					    4 Mar 1995					CYTUNE(8)

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