arch/all-pc/boot/grub/netboot/timer.c

   1 /* A couple of routines to implement a low-overhead timer for drivers */
   2
   3  /*
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License as
   6  * published by the Free Software Foundation; either version 2, or (at
   7  * your option) any later version.
   8  */
   9
  10 #include        "etherboot.h"
  11 #include        "timer.h"
  12
  13 void load_timer2(unsigned int ticks)
  14 {
  15         /* Set up the timer gate, turn off the speaker */
  16         outb((inb(PPC_PORTB) & ~PPCB_SPKR) | PPCB_T2GATE, PPC_PORTB);
  17         outb(TIMER2_SEL|WORD_ACCESS|MODE0|BINARY_COUNT, TIMER_MODE_PORT);
  18         outb(ticks & 0xFF, TIMER2_PORT);
  19         outb(ticks >> 8, TIMER2_PORT);
  20 }
  21
  22 #if defined(CONFIG_TSC_CURRTICKS)
  23 #define rdtsc(low,high) \
  24      __asm__ __volatile__("rdtsc" : "=a" (low), "=d" (high))
  25
  26 #define rdtscll(val) \
  27      __asm__ __volatile__ ("rdtsc" : "=A" (val))
  28
  29
  30 #define HZ TICKS_PER_SEC
  31 #define CLOCK_TICK_RATE 1193180U /* Underlying HZ */
  32 /* LATCH is used in the interval timer and ftape setup. */
  33 #define LATCH  ((CLOCK_TICK_RATE + HZ/2) / HZ)  /* For divider */
  34
  35
  36 /* ------ Calibrate the TSC -------
  37  * Return 2^32 * (1 / (TSC clocks per usec)) for do_fast_gettimeoffset().
  38  * Too much 64-bit arithmetic here to do this cleanly in C, and for
  39  * accuracy's sake we want to keep the overhead on the CTC speaker (channel 2)
  40  * output busy loop as low as possible. We avoid reading the CTC registers
  41  * directly because of the awkward 8-bit access mechanism of the 82C54
  42  * device.
  43  */
  44
  45 #define CALIBRATE_LATCH (5 * LATCH)
  46
  47 static unsigned long long calibrate_tsc(void)
  48 {
  49         /* Set the Gate high, disable speaker */
  50         outb((inb(0x61) & ~0x02) | 0x01, 0x61);
  51
  52         /*
  53          * Now let's take care of CTC channel 2
  54          *
  55          * Set the Gate high, program CTC channel 2 for mode 0,
  56          * (interrupt on terminal count mode), binary count,
  57          * load 5 * LATCH count, (LSB and MSB) to begin countdown.
  58          */
  59         outb(0xb0, 0x43);                       /* binary, mode 0, LSB/MSB, Ch 2 */
  60         outb(CALIBRATE_LATCH & 0xff, 0x42);     /* LSB of count */
  61         outb(CALIBRATE_LATCH >> 8, 0x42);       /* MSB of count */
  62
  63         {
  64                 unsigned long startlow, starthigh;
  65                 unsigned long endlow, endhigh;
  66                 unsigned long count;
  67
  68                 rdtsc(startlow,starthigh);
  69                 count = 0;
  70                 do {
  71                         count++;
  72                 } while ((inb(0x61) & 0x20) == 0);
  73                 rdtsc(endlow,endhigh);
  74
  75                 /* Error: ECTCNEVERSET */
  76                 if (count <= 1)
  77                         goto bad_ctc;
  78
  79                 /* 64-bit subtract - gcc just messes up with long longs */
  80                 __asm__("subl %2,%0\n\t"
  81                         "sbbl %3,%1"
  82                         :"=a" (endlow), "=d" (endhigh)
  83                         :"g" (startlow), "g" (starthigh),
  84                          "0" (endlow), "1" (endhigh));
  85
  86                 /* Error: ECPUTOOFAST */
  87                 if (endhigh)
  88                         goto bad_ctc;
  89
  90                 endlow /= 5;
  91                 return endlow;
  92         }
  93
  94         /*
  95          * The CTC wasn't reliable: we got a hit on the very first read,
  96          * or the CPU was so fast/slow that the quotient wouldn't fit in
  97          * 32 bits..
  98          */
  99 bad_ctc:
 100         printf("bad_ctc\n");
 101         return 0;
 102 }
 103
 104
 105 unsigned long currticks(void)
 106 {
 107         static unsigned long clocks_per_tick;
 108         unsigned long clocks_high, clocks_low;
 109         unsigned long currticks;
 110         if (!clocks_per_tick) {
 111                 clocks_per_tick = calibrate_tsc();
 112                 printf("clocks_per_tick = %d\n", clocks_per_tick);
 113         }
 114
 115         /* Read the Time Stamp Counter */
 116         rdtsc(clocks_low, clocks_high);
 117
 118         /* currticks = clocks / clocks_per_tick; */
 119         __asm__("divl %1"
 120                 :"=a" (currticks)
 121                 :"r" (clocks_per_tick), "0" (clocks_low), "d" (clocks_high));
 122
 123
 124         return currticks;
 125 }
 126
 127 #endif /* RTC_CURRTICKS */