root / hw / core / ptimer.c @ 49ab747f
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/*
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* General purpose implementation of a simple periodic countdown timer.
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*
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* Copyright (c) 2007 CodeSourcery.
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*
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* This code is licensed under the GNU LGPL.
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*/
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#include "hw/hw.h" |
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#include "qemu/timer.h" |
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#include "hw/ptimer.h" |
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#include "qemu/host-utils.h" |
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struct ptimer_state
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{ |
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uint8_t enabled; /* 0 = disabled, 1 = periodic, 2 = oneshot. */
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uint64_t limit; |
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uint64_t delta; |
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uint32_t period_frac; |
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int64_t period; |
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int64_t last_event; |
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int64_t next_event; |
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QEMUBH *bh; |
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QEMUTimer *timer; |
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}; |
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/* Use a bottom-half routine to avoid reentrancy issues. */
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static void ptimer_trigger(ptimer_state *s) |
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{ |
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if (s->bh) {
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qemu_bh_schedule(s->bh); |
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} |
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} |
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static void ptimer_reload(ptimer_state *s) |
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{ |
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if (s->delta == 0) { |
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ptimer_trigger(s); |
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s->delta = s->limit; |
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} |
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if (s->delta == 0 || s->period == 0) { |
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fprintf(stderr, "Timer with period zero, disabling\n");
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s->enabled = 0;
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return;
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} |
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s->last_event = s->next_event; |
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s->next_event = s->last_event + s->delta * s->period; |
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if (s->period_frac) {
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s->next_event += ((int64_t)s->period_frac * s->delta) >> 32;
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} |
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qemu_mod_timer(s->timer, s->next_event); |
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} |
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static void ptimer_tick(void *opaque) |
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{ |
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ptimer_state *s = (ptimer_state *)opaque; |
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ptimer_trigger(s); |
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s->delta = 0;
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if (s->enabled == 2) { |
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s->enabled = 0;
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} else {
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ptimer_reload(s); |
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} |
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} |
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uint64_t ptimer_get_count(ptimer_state *s) |
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{ |
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int64_t now; |
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uint64_t counter; |
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if (s->enabled) {
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now = qemu_get_clock_ns(vm_clock); |
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/* Figure out the current counter value. */
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if (now - s->next_event > 0 |
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|| s->period == 0) {
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/* Prevent timer underflowing if it should already have
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triggered. */
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counter = 0;
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} else {
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uint64_t rem; |
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uint64_t div; |
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int clz1, clz2;
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int shift;
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/* We need to divide time by period, where time is stored in
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rem (64-bit integer) and period is stored in period/period_frac
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(64.32 fixed point).
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Doing full precision division is hard, so scale values and
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do a 64-bit division. The result should be rounded down,
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so that the rounding error never causes the timer to go
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backwards.
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*/
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rem = s->next_event - now; |
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div = s->period; |
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clz1 = clz64(rem); |
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clz2 = clz64(div); |
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shift = clz1 < clz2 ? clz1 : clz2; |
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rem <<= shift; |
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div <<= shift; |
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if (shift >= 32) { |
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div |= ((uint64_t)s->period_frac << (shift - 32));
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} else {
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if (shift != 0) |
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div |= (s->period_frac >> (32 - shift));
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/* Look at remaining bits of period_frac and round div up if
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necessary. */
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if ((uint32_t)(s->period_frac << shift))
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div += 1;
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} |
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counter = rem / div; |
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} |
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} else {
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counter = s->delta; |
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} |
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return counter;
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} |
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void ptimer_set_count(ptimer_state *s, uint64_t count)
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{ |
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s->delta = count; |
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if (s->enabled) {
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s->next_event = qemu_get_clock_ns(vm_clock); |
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ptimer_reload(s); |
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} |
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} |
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void ptimer_run(ptimer_state *s, int oneshot) |
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{ |
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if (s->enabled) {
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return;
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} |
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if (s->period == 0) { |
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fprintf(stderr, "Timer with period zero, disabling\n");
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return;
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} |
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s->enabled = oneshot ? 2 : 1; |
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s->next_event = qemu_get_clock_ns(vm_clock); |
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ptimer_reload(s); |
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} |
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/* Pause a timer. Note that this may cause it to "lose" time, even if it
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is immediately restarted. */
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void ptimer_stop(ptimer_state *s)
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{ |
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if (!s->enabled)
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return;
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s->delta = ptimer_get_count(s); |
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qemu_del_timer(s->timer); |
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s->enabled = 0;
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} |
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/* Set counter increment interval in nanoseconds. */
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void ptimer_set_period(ptimer_state *s, int64_t period)
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{ |
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s->period = period; |
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s->period_frac = 0;
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if (s->enabled) {
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s->next_event = qemu_get_clock_ns(vm_clock); |
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ptimer_reload(s); |
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} |
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} |
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/* Set counter frequency in Hz. */
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void ptimer_set_freq(ptimer_state *s, uint32_t freq)
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{ |
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s->period = 1000000000ll / freq;
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s->period_frac = (1000000000ll << 32) / freq; |
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if (s->enabled) {
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s->next_event = qemu_get_clock_ns(vm_clock); |
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ptimer_reload(s); |
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} |
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} |
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/* Set the initial countdown value. If reload is nonzero then also set
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count = limit. */
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void ptimer_set_limit(ptimer_state *s, uint64_t limit, int reload) |
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{ |
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/*
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* Artificially limit timeout rate to something
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* achievable under QEMU. Otherwise, QEMU spends all
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* its time generating timer interrupts, and there
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* is no forward progress.
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* About ten microseconds is the fastest that really works
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* on the current generation of host machines.
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*/
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if (limit * s->period < 10000 && s->period) { |
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limit = 10000 / s->period;
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} |
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s->limit = limit; |
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if (reload)
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s->delta = limit; |
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if (s->enabled && reload) {
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s->next_event = qemu_get_clock_ns(vm_clock); |
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ptimer_reload(s); |
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} |
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} |
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const VMStateDescription vmstate_ptimer = {
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.name = "ptimer",
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.version_id = 1,
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.minimum_version_id = 1,
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.minimum_version_id_old = 1,
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.fields = (VMStateField[]) { |
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VMSTATE_UINT8(enabled, ptimer_state), |
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VMSTATE_UINT64(limit, ptimer_state), |
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VMSTATE_UINT64(delta, ptimer_state), |
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VMSTATE_UINT32(period_frac, ptimer_state), |
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VMSTATE_INT64(period, ptimer_state), |
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VMSTATE_INT64(last_event, ptimer_state), |
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VMSTATE_INT64(next_event, ptimer_state), |
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VMSTATE_TIMER(timer, ptimer_state), |
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VMSTATE_END_OF_LIST() |
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} |
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}; |
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ptimer_state *ptimer_init(QEMUBH *bh) |
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{ |
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ptimer_state *s; |
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s = (ptimer_state *)g_malloc0(sizeof(ptimer_state));
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s->bh = bh; |
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s->timer = qemu_new_timer_ns(vm_clock, ptimer_tick, s); |
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return s;
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} |