CYTUNE(8)						       System Administration							 CYTUNE(8)

NAME

       cytune - tune driver parameters for Cyclades-Z multiport serial card

SYNOPSIS

       cytune [options] 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 characters transferred over the monitoring interval.  It will also report the state of the FIFO.  The max-
       imum  number  of characters in the FIFO when an interrupt occurred, the instantaneous count of characters in the FIFO, and how many charac-
       ters 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 inter-
       rupt 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.

OPTIONS

       -s, --set-threshold 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, --set-flush 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, cur-
	      rently 0x20 (160ms), but soon to be 0x02 (10ms).	Units are 5 ms.

       -g, --get-threshold
	      Get the current threshold and timeout.

       -S, --set-default-threshold 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, inclusive, are permitted.

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

       -G, --get-glush
	      Get the default threshold and flush timeout values.

       -q, --stats
	      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 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 Linux Kernel Archive <ftp://ftp.kernel.org/pub/linux/utils/util-
       linux/>.

util-linux							  September 2011							 CYTUNE(8)