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