From c763b22a79ef10c0a961b24ae617980231681e06 Mon Sep 17 00:00:00 2001 From: phk Date: Wed, 26 Mar 2008 22:12:00 +0000 Subject: 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. --- sys/conf/options.amd64 | 2 -- sys/conf/options.i386 | 2 -- sys/conf/options.pc98 | 2 -- 3 files changed, 6 deletions(-) (limited to 'sys/conf') diff --git a/sys/conf/options.amd64 b/sys/conf/options.amd64 index 258b0b7..b05b770 100644 --- a/sys/conf/options.amd64 +++ b/sys/conf/options.amd64 @@ -21,8 +21,6 @@ LINPROCFS opt_dontuse.h LINSYSFS opt_dontuse.h NDISAPI opt_dontuse.h -CLK_CALIBRATION_LOOP opt_clock.h -CLK_USE_I8254_CALIBRATION opt_clock.h TIMER_FREQ opt_clock.h # options for serial support diff --git a/sys/conf/options.i386 b/sys/conf/options.i386 index 3fc3fb1..8cdaa5e 100644 --- a/sys/conf/options.i386 +++ b/sys/conf/options.i386 @@ -36,8 +36,6 @@ KVA_PAGES opt_global.h # Physical address extensions and support for >4G ram. As above. PAE opt_global.h -CLK_CALIBRATION_LOOP opt_clock.h -CLK_USE_I8254_CALIBRATION opt_clock.h TIMER_FREQ opt_clock.h CPU_ATHLON_SSE_HACK opt_cpu.h diff --git a/sys/conf/options.pc98 b/sys/conf/options.pc98 index 605870a..d910ff2 100644 --- a/sys/conf/options.pc98 +++ b/sys/conf/options.pc98 @@ -31,8 +31,6 @@ PECOFF_SUPPORT opt_dontuse.h # Change KVM size. Changes things all over the kernel. KVA_PAGES opt_global.h -CLK_CALIBRATION_LOOP opt_clock.h -CLK_USE_I8254_CALIBRATION opt_clock.h TIMER_FREQ opt_clock.h # options for serial support -- cgit v1.1