Reduce jitter of Pentium microtime() implementation by letting the counter
free-run and doing a subtract in microtime() rather than resetting the counter to zero at every clock tick. In combination with the changes to kern_clock.c, this should eliminate all the immediately obvious sources of systematic jitter in timekeeping on Pentium machines.
This commit is contained in:
wollman
parent
fab8249e23
commit
6cbc65227c
@ -34,7 +34,7 @@
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* SUCH DAMAGE.
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*
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* from: @(#)clock.c 7.2 (Berkeley) 5/12/91
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* $Id: clock.c,v 1.35 1995/06/11 19:31:18 rgrimes Exp $
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* $Id: clock.c,v 1.36 1995/08/25 19:24:56 bde Exp $
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*/
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/*
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@ -95,6 +95,8 @@ int disable_rtc_set = 0; /* disable resettodr() if != 0 */
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u_int idelayed;
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#ifdef I586_CPU
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int pentium_mhz;
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long long i586_ctr_bias;
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long long i586_last_tick;
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#endif
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u_int stat_imask = SWI_CLOCK_MASK;
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int timer0_max_count;
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@ -279,8 +281,6 @@ getit(void)
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}
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#ifdef I586_CPU
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static long long cycles_per_sec = 0;
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/*
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* Figure out how fast the cyclecounter runs. This must be run with
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* clock interrupts disabled, but with the timer/counter programmed
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@ -293,15 +293,15 @@ calibrate_cyclecounter(void)
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* Don't need volatile; should always use unsigned if 2's
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* complement arithmetic is desired.
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*/
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unsigned long long count, last_count;
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unsigned long long count;
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__asm __volatile(".byte 0xf,0x31" : "=A" (last_count));
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__asm __volatile(".byte 0x0f, 0x30" : : "A"(0LL), "c" (0x10));
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DELAY(1000000);
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__asm __volatile(".byte 0xf,0x31" : "=A" (count));
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/*
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* XX lose if the clock rate is not nearly a multiple of 1000000.
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*/
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pentium_mhz = ((count - last_count) + 500000) / 1000000;
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pentium_mhz = (count + 500000) / 1000000;
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}
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#endif
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@ -569,6 +569,15 @@ cpu_initclocks()
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/* XXX */ (inthand2_t *)clkintr, &clk_imask,
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/* unit */ 0);
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INTREN(IRQ0);
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#ifdef I586_CPU
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/*
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* Finish setting up anti-jitter measures.
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*/
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if (pentium_mhz) {
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I586_CYCLECTR(i586_last_tick);
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i586_ctr_bias = i586_last_tick;
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}
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#endif
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/* Initialize RTC. */
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writertc(RTC_STATUSA, rtc_statusa);
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@ -8,40 +8,35 @@
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#define _MACHINE_CLOCK_H_
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#ifdef I586_CPU
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#define I586_CYCLECTR(x) \
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__asm __volatile(".byte 0x0f, 0x31" : "=A" (x))
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/*
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* This resets the CPU cycle counter to zero, to make our
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* job easier in microtime(). Some fancy ifdefs could speed
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* this up for Pentium-only kernels.
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* We want this to be done as close as possible to the actual
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* timer incrementing in hardclock(), because there is a window
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* between the two where the value is no longer valid. Experimentation
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* may reveal a good precompensation to apply in microtime().
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* When we update the clock, we also update this bias value which is
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* automatically subtracted in microtime(). We assume that CPU_THISTICKLEN()
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* has been called at some point in the past, so that an appropriate value is
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* set up in i586_last_tick. (This works even if we are not being called
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* from hardclock because hardclock will have run before and will made the
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* call.)
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*/
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#define CPU_CLOCKUPDATE(otime, ntime) \
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do { \
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if(pentium_mhz) { \
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__asm __volatile("cli\n" \
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"movl (%2),%%eax\n" \
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"movl %%eax,(%1)\n" \
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"movl 4(%2),%%eax\n" \
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"movl %%eax,4(%1)\n" \
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"movl $0x10,%%ecx\n" \
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"xorl %%eax,%%eax\n" \
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"movl %%eax,%%edx\n" \
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".byte 0x0f, 0x30\n" \
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"sti\n" \
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"#%0%1%2" \
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: "=m"(*otime) /* no outputs */ \
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: "c"(otime), "b"(ntime) /* fake input */ \
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: "ax", "cx", "dx"); \
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disable_intr(); \
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i586_ctr_bias = i586_last_tick; \
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*(otime) = *(ntime); \
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enable_intr(); \
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} else { \
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*(otime) = *(ntime); \
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} \
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} while(0)
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#define CPU_THISTICKLEN(dflt) cpu_thisticklen(dflt)
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#else
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#define CPU_CLOCKUPDATE(otime, ntime) \
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(*(otime) = *(ntime))
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#define CPU_THISTICKLEN(dflt) dflt
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#endif
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#if defined(KERNEL) && !defined(LOCORE)
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@ -57,6 +52,8 @@ extern int adjkerntz;
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extern int disable_rtc_set;
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#ifdef I586_CPU
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extern int pentium_mhz;
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extern long long i586_last_tick;
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extern long long i586_ctr_bias;
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#endif
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extern int timer0_max_count;
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extern u_int timer0_overflow_threshold;
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@ -68,6 +65,24 @@ void calibrate_cyclecounter __P((void));
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void clkintr __P((struct clockframe frame));
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void rtcintr __P((struct clockframe frame));
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#ifdef I586_CPU
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static __inline u_long
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cpu_thisticklen(u_long dflt)
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{
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long long old;
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long rv;
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if (pentium_mhz) {
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old = i586_last_tick;
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I586_CYCLECTR(i586_last_tick);
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rv = (i586_last_tick - old) / pentium_mhz;
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} else {
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rv = dflt;
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}
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return rv;
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}
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#endif
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/*
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* Driver to clock driver interface.
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*/
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@ -34,7 +34,7 @@
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* SUCH DAMAGE.
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*
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* from: @(#)clock.c 7.2 (Berkeley) 5/12/91
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* $Id: clock.c,v 1.35 1995/06/11 19:31:18 rgrimes Exp $
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* $Id: clock.c,v 1.36 1995/08/25 19:24:56 bde Exp $
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*/
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/*
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@ -95,6 +95,8 @@ int disable_rtc_set = 0; /* disable resettodr() if != 0 */
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u_int idelayed;
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#ifdef I586_CPU
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int pentium_mhz;
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long long i586_ctr_bias;
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long long i586_last_tick;
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#endif
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u_int stat_imask = SWI_CLOCK_MASK;
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int timer0_max_count;
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@ -279,8 +281,6 @@ getit(void)
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}
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#ifdef I586_CPU
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static long long cycles_per_sec = 0;
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/*
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* Figure out how fast the cyclecounter runs. This must be run with
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* clock interrupts disabled, but with the timer/counter programmed
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@ -293,15 +293,15 @@ calibrate_cyclecounter(void)
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* Don't need volatile; should always use unsigned if 2's
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* complement arithmetic is desired.
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*/
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unsigned long long count, last_count;
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unsigned long long count;
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__asm __volatile(".byte 0xf,0x31" : "=A" (last_count));
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__asm __volatile(".byte 0x0f, 0x30" : : "A"(0LL), "c" (0x10));
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DELAY(1000000);
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__asm __volatile(".byte 0xf,0x31" : "=A" (count));
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/*
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* XX lose if the clock rate is not nearly a multiple of 1000000.
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*/
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pentium_mhz = ((count - last_count) + 500000) / 1000000;
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pentium_mhz = (count + 500000) / 1000000;
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}
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#endif
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@ -569,6 +569,15 @@ cpu_initclocks()
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/* XXX */ (inthand2_t *)clkintr, &clk_imask,
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/* unit */ 0);
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INTREN(IRQ0);
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#ifdef I586_CPU
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/*
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* Finish setting up anti-jitter measures.
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*/
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if (pentium_mhz) {
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I586_CYCLECTR(i586_last_tick);
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i586_ctr_bias = i586_last_tick;
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}
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#endif
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/* Initialize RTC. */
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writertc(RTC_STATUSA, rtc_statusa);
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@ -31,7 +31,7 @@
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* SUCH DAMAGE.
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*
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* from: Steve McCanne's microtime code
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* $Id: microtime.s,v 1.6 1994/08/13 17:45:09 wollman Exp $
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* $Id: microtime.s,v 1.7 1994/11/05 23:53:46 bde Exp $
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*/
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#include <machine/asmacros.h>
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@ -46,8 +46,6 @@ ENTRY(microtime)
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movl _pentium_mhz, %ecx
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testl %ecx, %ecx
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jne pentium_microtime
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#else
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xorl %ecx, %ecx # clear ecx
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#endif
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movb $TIMER_SEL0|TIMER_LATCH, %al # prepare to latch
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@ -173,9 +171,13 @@ common_microtime:
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ret
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.extern _i586_ctr_bias
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ALIGN_TEXT
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pentium_microtime:
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cli
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.byte 0x0f, 0x31 # RDTSC
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subl _i586_ctr_bias, %eax
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sbbl _i586_ctr_bias+4, %edx
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divl %ecx # get value in usec
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jmp common_microtime
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@ -34,7 +34,7 @@
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* SUCH DAMAGE.
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*
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* from: @(#)clock.c 7.2 (Berkeley) 5/12/91
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* $Id: clock.c,v 1.35 1995/06/11 19:31:18 rgrimes Exp $
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* $Id: clock.c,v 1.36 1995/08/25 19:24:56 bde Exp $
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*/
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/*
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@ -95,6 +95,8 @@ int disable_rtc_set = 0; /* disable resettodr() if != 0 */
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u_int idelayed;
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#ifdef I586_CPU
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int pentium_mhz;
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long long i586_ctr_bias;
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long long i586_last_tick;
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#endif
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u_int stat_imask = SWI_CLOCK_MASK;
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int timer0_max_count;
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@ -279,8 +281,6 @@ getit(void)
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}
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#ifdef I586_CPU
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static long long cycles_per_sec = 0;
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/*
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* Figure out how fast the cyclecounter runs. This must be run with
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* clock interrupts disabled, but with the timer/counter programmed
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@ -293,15 +293,15 @@ calibrate_cyclecounter(void)
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* Don't need volatile; should always use unsigned if 2's
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* complement arithmetic is desired.
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*/
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unsigned long long count, last_count;
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unsigned long long count;
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__asm __volatile(".byte 0xf,0x31" : "=A" (last_count));
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__asm __volatile(".byte 0x0f, 0x30" : : "A"(0LL), "c" (0x10));
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DELAY(1000000);
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__asm __volatile(".byte 0xf,0x31" : "=A" (count));
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/*
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* XX lose if the clock rate is not nearly a multiple of 1000000.
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*/
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pentium_mhz = ((count - last_count) + 500000) / 1000000;
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pentium_mhz = (count + 500000) / 1000000;
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}
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#endif
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@ -569,6 +569,15 @@ cpu_initclocks()
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/* XXX */ (inthand2_t *)clkintr, &clk_imask,
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/* unit */ 0);
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INTREN(IRQ0);
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#ifdef I586_CPU
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/*
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* Finish setting up anti-jitter measures.
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*/
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if (pentium_mhz) {
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I586_CYCLECTR(i586_last_tick);
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i586_ctr_bias = i586_last_tick;
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}
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#endif
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/* Initialize RTC. */
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writertc(RTC_STATUSA, rtc_statusa);
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@ -8,40 +8,35 @@
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#define _MACHINE_CLOCK_H_
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#ifdef I586_CPU
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#define I586_CYCLECTR(x) \
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__asm __volatile(".byte 0x0f, 0x31" : "=A" (x))
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/*
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* This resets the CPU cycle counter to zero, to make our
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* job easier in microtime(). Some fancy ifdefs could speed
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* this up for Pentium-only kernels.
|
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* We want this to be done as close as possible to the actual
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* timer incrementing in hardclock(), because there is a window
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* between the two where the value is no longer valid. Experimentation
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* may reveal a good precompensation to apply in microtime().
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* When we update the clock, we also update this bias value which is
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* automatically subtracted in microtime(). We assume that CPU_THISTICKLEN()
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* has been called at some point in the past, so that an appropriate value is
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* set up in i586_last_tick. (This works even if we are not being called
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* from hardclock because hardclock will have run before and will made the
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* call.)
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*/
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#define CPU_CLOCKUPDATE(otime, ntime) \
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do { \
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if(pentium_mhz) { \
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__asm __volatile("cli\n" \
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"movl (%2),%%eax\n" \
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"movl %%eax,(%1)\n" \
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"movl 4(%2),%%eax\n" \
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"movl %%eax,4(%1)\n" \
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"movl $0x10,%%ecx\n" \
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"xorl %%eax,%%eax\n" \
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"movl %%eax,%%edx\n" \
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".byte 0x0f, 0x30\n" \
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"sti\n" \
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"#%0%1%2" \
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: "=m"(*otime) /* no outputs */ \
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: "c"(otime), "b"(ntime) /* fake input */ \
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: "ax", "cx", "dx"); \
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disable_intr(); \
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i586_ctr_bias = i586_last_tick; \
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*(otime) = *(ntime); \
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enable_intr(); \
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} else { \
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*(otime) = *(ntime); \
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} \
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} while(0)
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#define CPU_THISTICKLEN(dflt) cpu_thisticklen(dflt)
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#else
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#define CPU_CLOCKUPDATE(otime, ntime) \
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(*(otime) = *(ntime))
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#define CPU_THISTICKLEN(dflt) dflt
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#endif
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#if defined(KERNEL) && !defined(LOCORE)
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@ -57,6 +52,8 @@ extern int adjkerntz;
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extern int disable_rtc_set;
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#ifdef I586_CPU
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extern int pentium_mhz;
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extern long long i586_last_tick;
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extern long long i586_ctr_bias;
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#endif
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extern int timer0_max_count;
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extern u_int timer0_overflow_threshold;
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@ -68,6 +65,24 @@ void calibrate_cyclecounter __P((void));
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void clkintr __P((struct clockframe frame));
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void rtcintr __P((struct clockframe frame));
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#ifdef I586_CPU
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static __inline u_long
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cpu_thisticklen(u_long dflt)
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{
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long long old;
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long rv;
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if (pentium_mhz) {
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old = i586_last_tick;
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I586_CYCLECTR(i586_last_tick);
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rv = (i586_last_tick - old) / pentium_mhz;
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} else {
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rv = dflt;
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}
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return rv;
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}
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#endif
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/*
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* Driver to clock driver interface.
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*/
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@ -34,7 +34,7 @@
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* SUCH DAMAGE.
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*
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* from: @(#)clock.c 7.2 (Berkeley) 5/12/91
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* $Id: clock.c,v 1.35 1995/06/11 19:31:18 rgrimes Exp $
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* $Id: clock.c,v 1.36 1995/08/25 19:24:56 bde Exp $
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*/
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/*
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@ -95,6 +95,8 @@ int disable_rtc_set = 0; /* disable resettodr() if != 0 */
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u_int idelayed;
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#ifdef I586_CPU
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int pentium_mhz;
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long long i586_ctr_bias;
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long long i586_last_tick;
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#endif
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u_int stat_imask = SWI_CLOCK_MASK;
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int timer0_max_count;
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@ -279,8 +281,6 @@ getit(void)
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}
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#ifdef I586_CPU
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static long long cycles_per_sec = 0;
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/*
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* Figure out how fast the cyclecounter runs. This must be run with
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* clock interrupts disabled, but with the timer/counter programmed
|
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@ -293,15 +293,15 @@ calibrate_cyclecounter(void)
|
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* Don't need volatile; should always use unsigned if 2's
|
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* complement arithmetic is desired.
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*/
|
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unsigned long long count, last_count;
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unsigned long long count;
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__asm __volatile(".byte 0xf,0x31" : "=A" (last_count));
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__asm __volatile(".byte 0x0f, 0x30" : : "A"(0LL), "c" (0x10));
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DELAY(1000000);
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__asm __volatile(".byte 0xf,0x31" : "=A" (count));
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/*
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* XX lose if the clock rate is not nearly a multiple of 1000000.
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*/
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pentium_mhz = ((count - last_count) + 500000) / 1000000;
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pentium_mhz = (count + 500000) / 1000000;
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}
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#endif
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@ -569,6 +569,15 @@ cpu_initclocks()
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/* XXX */ (inthand2_t *)clkintr, &clk_imask,
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/* unit */ 0);
|
||||
INTREN(IRQ0);
|
||||
#ifdef I586_CPU
|
||||
/*
|
||||
* Finish setting up anti-jitter measures.
|
||||
*/
|
||||
if (pentium_mhz) {
|
||||
I586_CYCLECTR(i586_last_tick);
|
||||
i586_ctr_bias = i586_last_tick;
|
||||
}
|
||||
#endif
|
||||
|
||||
/* Initialize RTC. */
|
||||
writertc(RTC_STATUSA, rtc_statusa);
|
||||
|
||||
@ -34,7 +34,7 @@
|
||||
* SUCH DAMAGE.
|
||||
*
|
||||
* from: @(#)clock.c 7.2 (Berkeley) 5/12/91
|
||||
* $Id: clock.c,v 1.35 1995/06/11 19:31:18 rgrimes Exp $
|
||||
* $Id: clock.c,v 1.36 1995/08/25 19:24:56 bde Exp $
|
||||
*/
|
||||
|
||||
/*
|
||||
@ -95,6 +95,8 @@ int disable_rtc_set = 0; /* disable resettodr() if != 0 */
|
||||
u_int idelayed;
|
||||
#ifdef I586_CPU
|
||||
int pentium_mhz;
|
||||
long long i586_ctr_bias;
|
||||
long long i586_last_tick;
|
||||
#endif
|
||||
u_int stat_imask = SWI_CLOCK_MASK;
|
||||
int timer0_max_count;
|
||||
@ -279,8 +281,6 @@ getit(void)
|
||||
}
|
||||
|
||||
#ifdef I586_CPU
|
||||
static long long cycles_per_sec = 0;
|
||||
|
||||
/*
|
||||
* Figure out how fast the cyclecounter runs. This must be run with
|
||||
* clock interrupts disabled, but with the timer/counter programmed
|
||||
@ -293,15 +293,15 @@ calibrate_cyclecounter(void)
|
||||
* Don't need volatile; should always use unsigned if 2's
|
||||
* complement arithmetic is desired.
|
||||
*/
|
||||
unsigned long long count, last_count;
|
||||
unsigned long long count;
|
||||
|
||||
__asm __volatile(".byte 0xf,0x31" : "=A" (last_count));
|
||||
__asm __volatile(".byte 0x0f, 0x30" : : "A"(0LL), "c" (0x10));
|
||||
DELAY(1000000);
|
||||
__asm __volatile(".byte 0xf,0x31" : "=A" (count));
|
||||
/*
|
||||
* XX lose if the clock rate is not nearly a multiple of 1000000.
|
||||
*/
|
||||
pentium_mhz = ((count - last_count) + 500000) / 1000000;
|
||||
pentium_mhz = (count + 500000) / 1000000;
|
||||
}
|
||||
#endif
|
||||
|
||||
@ -569,6 +569,15 @@ cpu_initclocks()
|
||||
/* XXX */ (inthand2_t *)clkintr, &clk_imask,
|
||||
/* unit */ 0);
|
||||
INTREN(IRQ0);
|
||||
#ifdef I586_CPU
|
||||
/*
|
||||
* Finish setting up anti-jitter measures.
|
||||
*/
|
||||
if (pentium_mhz) {
|
||||
I586_CYCLECTR(i586_last_tick);
|
||||
i586_ctr_bias = i586_last_tick;
|
||||
}
|
||||
#endif
|
||||
|
||||
/* Initialize RTC. */
|
||||
writertc(RTC_STATUSA, rtc_statusa);
|
||||
|
||||
Loading…
Reference in New Issue
Block a user