90 lines
2.1 KiB
C
90 lines
2.1 KiB
C
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#include <stdio.h>
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#include <time.h>
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#include <sys/time.h>
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#include <sys/times.h>
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#include <sys/types.h>
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#include <minix/u64.h>
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#include <minix/config.h>
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#include <minix/const.h>
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#include "sysutil.h"
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#define CALIBRATE_TICKS (HZ/5)
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#define MICROHZ 1000000 /* number of micros per second */
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#define MICROSPERTICK (MICROHZ/HZ) /* number of micros per HZ tick */
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static u32_t calib_tsc;
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static int calibrated = 0;
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int
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micro_delay_calibrate(void)
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{
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u64_t start, end, diff, hz;
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struct tms tms;
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unsigned long t = 0;
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/* Wait for clock to tick. */
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while(!t || (t == times(&tms)))
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t = times(&tms);
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t++;
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/* Wait for clock to tick CALIBRATE_TICKS times, and time
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* this using the TSC.
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*/
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read_tsc_64(&start);
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while(times(&tms) < t+CALIBRATE_TICKS) ;
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read_tsc_64(&end);
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diff = sub64(end, start);
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if(ex64hi(diff) != 0)
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panic(__FILE__,
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"micro_delay_calibrate: CALIBRATE_TICKS too high "
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"for TSC frequency\n", NO_NUM);
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calib_tsc = ex64lo(diff);
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printf("micro_delay_calibrate: "
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"%lu cycles/%d ticks of %d Hz; %lu cycles/s\n",
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calib_tsc, CALIBRATE_TICKS, HZ,
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div64u(mul64u(calib_tsc, HZ), CALIBRATE_TICKS));
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calibrated = 1;
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return OK;
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}
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int
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micro_delay(u32_t micros)
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{
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u64_t now, end;
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/* Start of delay. */
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read_tsc_64(&now);
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/* We have to be calibrated. */
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if(!calibrated) {
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int r;
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printf("micro_delay: calibrating\n");
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if((r=micro_delay_calibrate()) != OK)
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panic(__FILE__, "micro_delay: calibrate failed\n", r);
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}
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/* We have to know when to end the delay. */
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end = add64u(now, div64u(mul64u(calib_tsc,
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micros * HZ / CALIBRATE_TICKS), MICROHZ));
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/* If we have to wait for at least one HZ tick, use the regular
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* tickdelay first. Round downwards on purpose, so the average
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* half-tick we wait short (depending on where in the current tick
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* we call tickdelay). We can correct for both overhead of tickdelay
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* itself and the short wait in the busywait later.
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*/
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if(micros >= MICROSPERTICK)
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tickdelay(micros*HZ/MICROHZ);
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/* Wait (the rest) of the delay time using busywait. */
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while(cmp64(now, end) < 0)
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read_tsc_64(&now);
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return OK;
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}
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