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 charac-
       ters 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 maximum  num-
       ber  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  thresh-
              old, 11 max, 11 now
                 166.259866  interrupts/second, 1828.858521 char-

       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 hard-
       ware 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

       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 monitor-
       ing  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 thresh-
       old 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 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,  inclu-
              sive, 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.

       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  (, with modifications by
       Rik Faith (



                            4 Mar 1995                          1