cvs commit: src/sys/isa psm.c

[Alfred Perlstein]

alfred      2003/12/11 03:28:11 PST

  FreeBSD src repository

  Modified files:
    sys/isa              psm.c 
  Log:
  Significantly reduce the "jitter" that is typical for PS/2 mice
  when using a KVM.
  
  There is no actual solution possible, but this gets us pretty close.
  
  Typically when switching back to a FreeBSD box and moving the mouse
  wild data is produced, because the protocol's validation/checksum
  system is extremely weak it is impossible to determine that we're
  out of sync before dropping several bogus packets to user land.
  
  The actual solution that appears to offer the best clamping of
  jitter is to buffer the mouse packets if we've not seen mouse
  activity for more than .5 seconds.  Then waiting to flush that data
  for 1/20th of a second.  If within that 20th of a second we get any
  packets that do fail the weak test we drop the entire queue and
  back off accepting data from the mouse for 2 seconds and then repeat
  the whole deal.
  
  You can still get _some_ jitter, notably if you switch to the FreeBSD
  box, then move the mouse just enough to generate one or two packets.
  Those packets may be bogus, but may still pass the validity check.
  
  One way to finally kill the problem once and for all is to check
  the initial packets for "wild" values.  Typically one sees packets
  in the +/-60 range during normal operation, however when bogus data
  is generated it's typically near the outer range of +/-120 or more,
  those packets would be a good candidate for dropping or clamping.
  
  I've been running with this for several weeks now and it has
  significantly helped me stay sane even with a piece of junk Belkin
  KVM causing wild jitter each and every time I switch.
  
  Lastly I'd like to note that my experience with Windows shows me that
  somehow the Microsoft PS/2 driver typically avoids this problem, but
  that may only be possible when running the mouse in a dumb-ed down PS/2
  mode that Belkin recommends on their site.
  
  Revision  Changes    Path
  1.63      +256 -110  src/sys/isa/psm.c