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

NAME
       cytune - Tune driver parameters for Cyclades-Z multiport serial card

SYNOPSIS
       cytune [-q [-i interval]] [{-s|-S} value] [-g|-G] [{-t|-T} timeout] 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, 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.

       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 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.

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.

       -S value
	      Set  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,  inclu-
	      sive, are permitted.

       -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  correctly.   cytune
       should prevent this, but does not.

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

SEE ALSO
       setserial(8)

AVAILABILITY
       The  cytune command is part of the util-linux package and is available from ftp://ftp.ker-
       nel.org/pub/linux/utils/util-linux/.

					    4 Mar 1995					CYTUNE(8)
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