cvs commit: src/sys/amd64/conf NOTES src/sys/amd64/isa clock.c src/sys/conf options.amd64 options.i386 options.pc98 src/sys/i386/conf NOTES src/sys/i386/isa clock.c src/sys/pc98/cbus clock.c src/sys/pc98/conf NOTES

[Poul-Henning Kamp]

phk         2008-03-26 22:12:00 UTC

  FreeBSD src repository

  Modified files:
    sys/amd64/conf       NOTES 
    sys/amd64/isa        clock.c 
    sys/conf             options.amd64 options.i386 options.pc98 
    sys/i386/conf        NOTES 
    sys/i386/isa         clock.c 
    sys/pc98/cbus        clock.c 
    sys/pc98/conf        NOTES 
  Log:
  Back in the good old days, PC's had random pieces of rock for
  frequency generation and what frequency the generated was anyones
  guess.
  
  In general the 32.768kHz RTC clock x-tal was the best, because that
  was a regular wrist-watch Xtal, whereas the X-tal generating the
  ISA bus frequency was much lower quality, often costing as much as
  several cents a piece, so it made good sense to check the ISA bus
  frequency against the RTC clock.
  
  The other relevant property of those machines, is that they
  typically had no more than 16MB RAM.
  
  These days, CPU chips croak if their clocks are not tightly within
  specs and all necessary frequencies are derived from the master
  crystal by means if PLL's.
  
  Considering that it takes on average 1.5 second to calibrate the
  frequency of the i8254 counter, that more likely than not, we will
  not actually use the result of the calibration, and as the final
  clincher, we seldom use the i8254 for anything besides BEL in
  syscons anyway, it has become time to drop the calibration code.
  
  If you need to tell the system what frequency your i8254 runs,
  you can do so from the loader using hw.i8254.freq or using the
  sysctl kern.timecounter.tc.i8254.frequency.
  
  Revision  Changes    Path
  1.77      +0 -13     src/sys/amd64/conf/NOTES
  1.241     +0 -112    src/sys/amd64/isa/clock.c
  1.31      +0 -2      src/sys/conf/options.amd64
  1.240     +0 -2      src/sys/conf/options.i386
  1.202     +0 -2      src/sys/conf/options.pc98
  1.1252    +0 -13     src/sys/i386/conf/NOTES
  1.245     +0 -122    src/sys/i386/isa/clock.c
  1.166     +0 -98     src/sys/pc98/cbus/clock.c
  1.87      +0 -17     src/sys/pc98/conf/NOTES