cytune man page on Archlinux

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CYTUNE(8)		     System Administration		     CYTUNE(8)

       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	inter‐
       ruption	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

       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 num‐
       ber of characters in the FIFO when an interrupt occurred, the instanta‐
       neous 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
		 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 con‐
       trol 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  con‐
       trolled	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 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, currently 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.

       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 ⟨

util-linux			September 2011			     CYTUNE(8)

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