hw/core/ptimer.c

   1 /*
   2  * General purpose implementation of a simple periodic countdown timer.
   3  *
   4  * Copyright (c) 2007 CodeSourcery.
   5  *
   6  * This code is licensed under the GNU LGPL.
   7  */
   8 #include "qemu/osdep.h"
   9 #include "hw/hw.h"
  10 #include "qemu/timer.h"
  11 #include "hw/ptimer.h"
  12 #include "qemu/host-utils.h"
  13 #include "sysemu/replay.h"
  14
  15 struct ptimer_state
  16 {
  17     uint8_t enabled; /* 0 = disabled, 1 = periodic, 2 = oneshot.  */
  18     uint64_t limit;
  19     uint64_t delta;
  20     uint32_t period_frac;
  21     int64_t period;
  22     int64_t last_event;
  23     int64_t next_event;
  24     QEMUBH *bh;
  25     QEMUTimer *timer;
  26 };
  27
  28 /* Use a bottom-half routine to avoid reentrancy issues.  */
  29 static void ptimer_trigger(ptimer_state *s)
  30 {
  31     if (s->bh) {
  32         replay_bh_schedule_event(s->bh);
  33     }
  34 }
  35
  36 static void ptimer_reload(ptimer_state *s)
  37 {
  38     if (s->delta == 0) {
  39         ptimer_trigger(s);
  40         s->delta = s->limit;
  41     }
  42     if (s->delta == 0 || s->period == 0) {
  43         fprintf(stderr, "Timer with period zero, disabling\n");
  44         s->enabled = 0;
  45         return;
  46     }
  47
  48     s->last_event = s->next_event;
  49     s->next_event = s->last_event + s->delta * s->period;
  50     if (s->period_frac) {
  51         s->next_event += ((int64_t)s->period_frac * s->delta) >> 32;
  52     }
  53     timer_mod(s->timer, s->next_event);
  54 }
  55
  56 static void ptimer_tick(void *opaque)
  57 {
  58     ptimer_state *s = (ptimer_state *)opaque;
  59     ptimer_trigger(s);
  60     s->delta = 0;
  61     if (s->enabled == 2) {
  62         s->enabled = 0;
  63     } else {
  64         ptimer_reload(s);
  65     }
  66 }
  67
  68 uint64_t ptimer_get_count(ptimer_state *s)
  69 {
  70     int64_t now;
  71     uint64_t counter;
  72
  73     if (s->enabled) {
  74         now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
  75         /* Figure out the current counter value.  */
  76         if (now - s->next_event > 0
  77             || s->period == 0) {
  78             /* Prevent timer underflowing if it should already have
  79                triggered.  */
  80             counter = 0;
  81         } else {
  82             uint64_t rem;
  83             uint64_t div;
  84             int clz1, clz2;
  85             int shift;
  86
  87             /* We need to divide time by period, where time is stored in
  88                rem (64-bit integer) and period is stored in period/period_frac
  89                (64.32 fixed point).
  90
  91                Doing full precision division is hard, so scale values and
  92                do a 64-bit division.  The result should be rounded down,
  93                so that the rounding error never causes the timer to go
  94                backwards.
  95             */
  96
  97             rem = s->next_event - now;
  98             div = s->period;
  99
 100             clz1 = clz64(rem);
 101             clz2 = clz64(div);
 102             shift = clz1 < clz2 ? clz1 : clz2;
 103
 104             rem <<= shift;
 105             div <<= shift;
 106             if (shift >= 32) {
 107                 div |= ((uint64_t)s->period_frac << (shift - 32));
 108             } else {
 109                 if (shift != 0)
 110                     div |= (s->period_frac >> (32 - shift));
 111                 /* Look at remaining bits of period_frac and round div up if
 112                    necessary.  */
 113                 if ((uint32_t)(s->period_frac << shift))
 114                     div += 1;
 115             }
 116             counter = rem / div;
 117         }
 118     } else {
 119         counter = s->delta;
 120     }
 121     return counter;
 122 }
 123
 124 void ptimer_set_count(ptimer_state *s, uint64_t count)
 125 {
 126     s->delta = count;
 127     if (s->enabled) {
 128         s->next_event = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 129         ptimer_reload(s);
 130     }
 131 }
 132
 133 void ptimer_run(ptimer_state *s, int oneshot)
 134 {
 135     if (s->enabled) {
 136         return;
 137     }
 138     if (s->period == 0) {
 139         fprintf(stderr, "Timer with period zero, disabling\n");
 140         return;
 141     }
 142     s->enabled = oneshot ? 2 : 1;
 143     s->next_event = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 144     ptimer_reload(s);
 145 }
 146
 147 /* Pause a timer.  Note that this may cause it to "lose" time, even if it
 148    is immediately restarted.  */
 149 void ptimer_stop(ptimer_state *s)
 150 {
 151     if (!s->enabled)
 152         return;
 153
 154     s->delta = ptimer_get_count(s);
 155     timer_del(s->timer);
 156     s->enabled = 0;
 157 }
 158
 159 /* Set counter increment interval in nanoseconds.  */
 160 void ptimer_set_period(ptimer_state *s, int64_t period)
 161 {
 162     s->period = period;
 163     s->period_frac = 0;
 164     if (s->enabled) {
 165         s->next_event = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 166         ptimer_reload(s);
 167     }
 168 }
 169
 170 /* Set counter frequency in Hz.  */
 171 void ptimer_set_freq(ptimer_state *s, uint32_t freq)
 172 {
 173     s->period = 1000000000ll / freq;
 174     s->period_frac = (1000000000ll << 32) / freq;
 175     if (s->enabled) {
 176         s->next_event = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 177         ptimer_reload(s);
 178     }
 179 }
 180
 181 /* Set the initial countdown value.  If reload is nonzero then also set
 182    count = limit.  */
 183 void ptimer_set_limit(ptimer_state *s, uint64_t limit, int reload)
 184 {
 185     /*
 186      * Artificially limit timeout rate to something
 187      * achievable under QEMU.  Otherwise, QEMU spends all
 188      * its time generating timer interrupts, and there
 189      * is no forward progress.
 190      * About ten microseconds is the fastest that really works
 191      * on the current generation of host machines.
 192      */
 193
 194     if (!use_icount && limit * s->period < 10000 && s->period) {
 195         limit = 10000 / s->period;
 196     }
 197
 198     s->limit = limit;
 199     if (reload)
 200         s->delta = limit;
 201     if (s->enabled && reload) {
 202         s->next_event = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 203         ptimer_reload(s);
 204     }
 205 }
 206
 207 const VMStateDescription vmstate_ptimer = {
 208     .name = "ptimer",
 209     .version_id = 1,
 210     .minimum_version_id = 1,
 211     .fields = (VMStateField[]) {
 212         VMSTATE_UINT8(enabled, ptimer_state),
 213         VMSTATE_UINT64(limit, ptimer_state),
 214         VMSTATE_UINT64(delta, ptimer_state),
 215         VMSTATE_UINT32(period_frac, ptimer_state),
 216         VMSTATE_INT64(period, ptimer_state),
 217         VMSTATE_INT64(last_event, ptimer_state),
 218         VMSTATE_INT64(next_event, ptimer_state),
 219         VMSTATE_TIMER_PTR(timer, ptimer_state),
 220         VMSTATE_END_OF_LIST()
 221     }
 222 };
 223
 224 ptimer_state *ptimer_init(QEMUBH *bh)
 225 {
 226     ptimer_state *s;
 227
 228     s = (ptimer_state *)g_malloc0(sizeof(ptimer_state));
 229     s->bh = bh;
 230     s->timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, ptimer_tick, s);
 231     return s;
 232 }