hw/ptimer.c

   1 /*
   2  * General purpose implementation of a simple periodic countdown timer.
   3  *
   4  * Copyright (c) 2007 CodeSourcery.
   5  *
   6  * This code is licenced under the GNU LGPL.
   7  */
   8 #include "hw.h"
   9 #include "qemu-timer.h"
  10 #include "host-utils.h"
  11
  12 struct ptimer_state
  13 {
  14     uint8_t enabled; /* 0 = disabled, 1 = periodic, 2 = oneshot.  */
  15     uint64_t limit;
  16     uint64_t delta;
  17     uint32_t period_frac;
  18     int64_t period;
  19     int64_t last_event;
  20     int64_t next_event;
  21     QEMUBH *bh;
  22     QEMUTimer *timer;
  23 };
  24
  25 /* Use a bottom-half routine to avoid reentrancy issues.  */
  26 static void ptimer_trigger(ptimer_state *s)
  27 {
  28     if (s->bh) {
  29         qemu_bh_schedule(s->bh);
  30     }
  31 }
  32
  33 static void ptimer_reload(ptimer_state *s)
  34 {
  35     if (s->delta == 0) {
  36         ptimer_trigger(s);
  37         s->delta = s->limit;
  38     }
  39     if (s->delta == 0 || s->period == 0) {
  40         fprintf(stderr, "Timer with period zero, disabling\n");
  41         s->enabled = 0;
  42         return;
  43     }
  44
  45     s->last_event = s->next_event;
  46     s->next_event = s->last_event + s->delta * s->period;
  47     if (s->period_frac) {
  48         s->next_event += ((int64_t)s->period_frac * s->delta) >> 32;
  49     }
  50     qemu_mod_timer(s->timer, s->next_event);
  51 }
  52
  53 static void ptimer_tick(void *opaque)
  54 {
  55     ptimer_state *s = (ptimer_state *)opaque;
  56     ptimer_trigger(s);
  57     s->delta = 0;
  58     if (s->enabled == 2) {
  59         s->enabled = 0;
  60     } else {
  61         ptimer_reload(s);
  62     }
  63 }
  64
  65 uint64_t ptimer_get_count(ptimer_state *s)
  66 {
  67     int64_t now;
  68     uint64_t counter;
  69
  70     if (s->enabled) {
  71         now = qemu_get_clock_ns(vm_clock);
  72         /* Figure out the current counter value.  */
  73         if (now - s->next_event > 0
  74             || s->period == 0) {
  75             /* Prevent timer underflowing if it should already have
  76                triggered.  */
  77             counter = 0;
  78         } else {
  79             uint64_t rem;
  80             uint64_t div;
  81             int clz1, clz2;
  82             int shift;
  83
  84             /* We need to divide time by period, where time is stored in
  85                rem (64-bit integer) and period is stored in period/period_frac
  86                (64.32 fixed point).
  87
  88                Doing full precision division is hard, so scale values and
  89                do a 64-bit division.  The result should be rounded down,
  90                so that the rounding error never causes the timer to go
  91                backwards.
  92             */
  93
  94             rem = s->next_event - now;
  95             div = s->period;
  96
  97             clz1 = clz64(rem);
  98             clz2 = clz64(div);
  99             shift = clz1 < clz2 ? clz1 : clz2;
 100
 101             rem <<= shift;
 102             div <<= shift;
 103             if (shift >= 32) {
 104                 div |= ((uint64_t)s->period_frac << (shift - 32));
 105             } else {
 106                 if (shift != 0)
 107                     div |= (s->period_frac >> (32 - shift));
 108                 /* Look at remaining bits of period_frac and round div up if
 109                    necessary.  */
 110                 if ((uint32_t)(s->period_frac << shift))
 111                     div += 1;
 112             }
 113             counter = rem / div;
 114         }
 115     } else {
 116         counter = s->delta;
 117     }
 118     return counter;
 119 }
 120
 121 void ptimer_set_count(ptimer_state *s, uint64_t count)
 122 {
 123     s->delta = count;
 124     if (s->enabled) {
 125         s->next_event = qemu_get_clock_ns(vm_clock);
 126         ptimer_reload(s);
 127     }
 128 }
 129
 130 void ptimer_run(ptimer_state *s, int oneshot)
 131 {
 132     if (s->enabled) {
 133         return;
 134     }
 135     if (s->period == 0) {
 136         fprintf(stderr, "Timer with period zero, disabling\n");
 137         return;
 138     }
 139     s->enabled = oneshot ? 2 : 1;
 140     s->next_event = qemu_get_clock_ns(vm_clock);
 141     ptimer_reload(s);
 142 }
 143
 144 /* Pause a timer.  Note that this may cause it to "lose" time, even if it
 145    is immediately restarted.  */
 146 void ptimer_stop(ptimer_state *s)
 147 {
 148     if (!s->enabled)
 149         return;
 150
 151     s->delta = ptimer_get_count(s);
 152     qemu_del_timer(s->timer);
 153     s->enabled = 0;
 154 }
 155
 156 /* Set counter increment interval in nanoseconds.  */
 157 void ptimer_set_period(ptimer_state *s, int64_t period)
 158 {
 159     s->period = period;
 160     s->period_frac = 0;
 161     if (s->enabled) {
 162         s->next_event = qemu_get_clock_ns(vm_clock);
 163         ptimer_reload(s);
 164     }
 165 }
 166
 167 /* Set counter frequency in Hz.  */
 168 void ptimer_set_freq(ptimer_state *s, uint32_t freq)
 169 {
 170     s->period = 1000000000ll / freq;
 171     s->period_frac = (1000000000ll << 32) / freq;
 172     if (s->enabled) {
 173         s->next_event = qemu_get_clock_ns(vm_clock);
 174         ptimer_reload(s);
 175     }
 176 }
 177
 178 /* Set the initial countdown value.  If reload is nonzero then also set
 179    count = limit.  */
 180 void ptimer_set_limit(ptimer_state *s, uint64_t limit, int reload)
 181 {
 182     s->limit = limit;
 183     if (reload)
 184         s->delta = limit;
 185     if (s->enabled && reload) {
 186         s->next_event = qemu_get_clock_ns(vm_clock);
 187         ptimer_reload(s);
 188     }
 189 }
 190
 191 const VMStateDescription vmstate_ptimer = {
 192     .name = "ptimer",
 193     .version_id = 1,
 194     .minimum_version_id = 1,
 195     .minimum_version_id_old = 1,
 196     .fields      = (VMStateField[]) {
 197         VMSTATE_UINT8(enabled, ptimer_state),
 198         VMSTATE_UINT64(limit, ptimer_state),
 199         VMSTATE_UINT64(delta, ptimer_state),
 200         VMSTATE_UINT32(period_frac, ptimer_state),
 201         VMSTATE_INT64(period, ptimer_state),
 202         VMSTATE_INT64(last_event, ptimer_state),
 203         VMSTATE_INT64(next_event, ptimer_state),
 204         VMSTATE_TIMER(timer, ptimer_state),
 205         VMSTATE_END_OF_LIST()
 206     }
 207 };
 208
 209 ptimer_state *ptimer_init(QEMUBH *bh)
 210 {
 211     ptimer_state *s;
 212
 213     s = (ptimer_state *)qemu_mallocz(sizeof(ptimer_state));
 214     s->bh = bh;
 215     s->timer = qemu_new_timer_ns(vm_clock, ptimer_tick, s);
 216     return s;
 217 }