hw/core/ptimer.c - qemu - Git at Google

 /*
  * General purpose implementation of a simple periodic countdown timer.
  *
  * Copyright (c) 2007 CodeSourcery.
  *
  * This code is licensed under the GNU LGPL.
  */

 #include "qemu/osdep.h"
 #include "hw/ptimer.h"
 #include "migration/vmstate.h"
 #include "qemu/host-utils.h"
 #include "exec/replay-core.h"
 #include "sysemu/cpu-timers.h"
 #include "sysemu/qtest.h"
 #include "block/aio.h"
 #include "hw/clock.h"

 #define DELTA_ADJUST     1
 #define DELTA_NO_ADJUST -1

 struct ptimer_state
 {
     uint8_t enabled; /* 0 = disabled, 1 = periodic, 2 = oneshot.  */
     uint64_t limit;
     uint64_t delta;
     uint32_t period_frac;
     int64_t period;
     int64_t last_event;
     int64_t next_event;
     uint8_t policy_mask;
     QEMUTimer *timer;
     ptimer_cb callback;
     void *callback_opaque;
     /*
      * These track whether we're in a transaction block, and if we
      * need to do a timer reload when the block finishes. They don't
      * need to be migrated because migration can never happen in the
      * middle of a transaction block.
      */
     bool in_transaction;
     bool need_reload;
 };

 /* Use a bottom-half routine to avoid reentrancy issues.  */
 static void ptimer_trigger(ptimer_state *s)
 {
     s->callback(s->callback_opaque);
 }

 static void ptimer_reload(ptimer_state *s, int delta_adjust)
 {
     uint32_t period_frac;
     uint64_t period;
     uint64_t delta;
     bool suppress_trigger = false;

     /*
      * Note that if delta_adjust is 0 then we must be here because of
      * a count register write or timer start, not because of timer expiry.
      * In that case the policy might require us to suppress the timer trigger
      * that we would otherwise generate for a zero delta.
      */
     if (delta_adjust == 0 &&
         (s->policy_mask & PTIMER_POLICY_TRIGGER_ONLY_ON_DECREMENT)) {
         suppress_trigger = true;
     }
     if (s->delta == 0 && !(s->policy_mask & PTIMER_POLICY_NO_IMMEDIATE_TRIGGER)
         && !suppress_trigger) {
         ptimer_trigger(s);
     }

     /*
      * Note that ptimer_trigger() might call the device callback function,
      * which can then modify timer state, so we must not cache any fields
      * from ptimer_state until after we have called it.
      */
     delta = s->delta;
     period = s->period;
     period_frac = s->period_frac;

     if (delta == 0 && !(s->policy_mask & PTIMER_POLICY_NO_IMMEDIATE_RELOAD)) {
         delta = s->delta = s->limit;
     }

     if (s->period == 0) {
         if (!qtest_enabled()) {
             fprintf(stderr, "Timer with period zero, disabling\n");
         }
         timer_del(s->timer);
         s->enabled = 0;
         return;
     }

     if (s->policy_mask & PTIMER_POLICY_WRAP_AFTER_ONE_PERIOD) {
         if (delta_adjust != DELTA_NO_ADJUST) {
             delta += delta_adjust;
         }
     }

     if (delta == 0 && (s->policy_mask & PTIMER_POLICY_CONTINUOUS_TRIGGER)) {
         if (s->enabled == 1 && s->limit == 0) {
             delta = 1;
         }
     }

     if (delta == 0 && (s->policy_mask & PTIMER_POLICY_NO_IMMEDIATE_TRIGGER)) {
         if (delta_adjust != DELTA_NO_ADJUST) {
             delta = 1;
         }
     }

     if (delta == 0 && (s->policy_mask & PTIMER_POLICY_NO_IMMEDIATE_RELOAD)) {
         if (s->enabled == 1 && s->limit != 0) {
             delta = 1;
         }
     }

     if (delta == 0) {
         if (s->enabled == 0) {
             /* trigger callback disabled the timer already */
             return;
         }
         if (!qtest_enabled()) {
             fprintf(stderr, "Timer with delta zero, disabling\n");
         }
         timer_del(s->timer);
         s->enabled = 0;
         return;
     }

     /*
      * Artificially limit timeout rate to something
      * achievable under QEMU.  Otherwise, QEMU spends all
      * its time generating timer interrupts, and there
      * is no forward progress.
      * About ten microseconds is the fastest that really works
      * on the current generation of host machines.
      */

     if (s->enabled == 1 && (delta * period < 10000) &&
         !icount_enabled() && !qtest_enabled()) {
         period = 10000 / delta;
         period_frac = 0;
     }

     s->last_event = s->next_event;
     s->next_event = s->last_event + delta * period;
     if (period_frac) {
         s->next_event += ((int64_t)period_frac * delta) >> 32;
     }
     timer_mod(s->timer, s->next_event);
 }

 static void ptimer_tick(void *opaque)
 {
     ptimer_state *s = (ptimer_state *)opaque;
     bool trigger = true;

     /*
      * We perform all the tick actions within a begin/commit block
      * because the callback function that ptimer_trigger() calls
      * might make calls into the ptimer APIs that provoke another
      * trigger, and we want that to cause the callback function
      * to be called iteratively, not recursively.
      */
     ptimer_transaction_begin(s);

     if (s->enabled == 2) {
         s->delta = 0;
         s->enabled = 0;
     } else {
         int delta_adjust = DELTA_ADJUST;

         if (s->delta == 0 || s->limit == 0) {
             /* If a "continuous trigger" policy is not used and limit == 0,
                we should error out. delta == 0 means that this tick is
                caused by a "no immediate reload" policy, so it shouldn't
                be adjusted.  */
             delta_adjust = DELTA_NO_ADJUST;
         }

         if (!(s->policy_mask & PTIMER_POLICY_NO_IMMEDIATE_TRIGGER)) {
             /* Avoid re-trigger on deferred reload if "no immediate trigger"
                policy isn't used.  */
             trigger = (delta_adjust == DELTA_ADJUST);
         }

         s->delta = s->limit;

         ptimer_reload(s, delta_adjust);
     }

     if (trigger) {
         ptimer_trigger(s);
     }

     ptimer_transaction_commit(s);
 }

 uint64_t ptimer_get_count(ptimer_state *s)
 {
     uint64_t counter;

     if (s->enabled && s->delta != 0) {
         int64_t now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
         int64_t next = s->next_event;
         int64_t last = s->last_event;
         bool expired = (now - next >= 0);
         bool oneshot = (s->enabled == 2);

         /* Figure out the current counter value.  */
         if (expired) {
             /* Prevent timer underflowing if it should already have
                triggered.  */
             counter = 0;
         } else {
             uint64_t rem;
             uint64_t div;
             int clz1, clz2;
             int shift;
             uint32_t period_frac = s->period_frac;
             uint64_t period = s->period;

             if (!oneshot && (s->delta * period < 10000) &&
                 !icount_enabled() && !qtest_enabled()) {
                 period = 10000 / s->delta;
                 period_frac = 0;
             }

             /* We need to divide time by period, where time is stored in
                rem (64-bit integer) and period is stored in period/period_frac
                (64.32 fixed point).

                Doing full precision division is hard, so scale values and
                do a 64-bit division.  The result should be rounded down,
                so that the rounding error never causes the timer to go
                backwards.
             */

             rem = next - now;
             div = period;

             clz1 = clz64(rem);
             clz2 = clz64(div);
             shift = clz1 < clz2 ? clz1 : clz2;

             rem <<= shift;
             div <<= shift;
             if (shift >= 32) {
                 div |= ((uint64_t)period_frac << (shift - 32));
             } else {
                 if (shift != 0)
                     div |= (period_frac >> (32 - shift));
                 /* Look at remaining bits of period_frac and round div up if
                    necessary.  */
                 if ((uint32_t)(period_frac << shift))
                     div += 1;
             }
             counter = rem / div;

             if (s->policy_mask & PTIMER_POLICY_WRAP_AFTER_ONE_PERIOD) {
                 /* Before wrapping around, timer should stay with counter = 0
                    for a one period.  */
                 if (!oneshot && s->delta == s->limit) {
                     if (now == last) {
                         /* Counter == delta here, check whether it was
                            adjusted and if it was, then right now it is
                            that "one period".  */
                         if (counter == s->limit + DELTA_ADJUST) {
                             return 0;
                         }
                     } else if (counter == s->limit) {
                         /* Since the counter is rounded down and now != last,
                            the counter == limit means that delta was adjusted
                            by +1 and right now it is that adjusted period.  */
                         return 0;
                     }
                 }
             }
         }

         if (s->policy_mask & PTIMER_POLICY_NO_COUNTER_ROUND_DOWN) {
             /* If now == last then delta == limit, i.e. the counter already
                represents the correct value. It would be rounded down a 1ns
                later.  */
             if (now != last) {
                 counter += 1;
             }
         }
     } else {
         counter = s->delta;
     }
     return counter;
 }

 void ptimer_set_count(ptimer_state *s, uint64_t count)
 {
     assert(s->in_transaction);
     s->delta = count;
     if (s->enabled) {
         s->need_reload = true;
     }
 }

 void ptimer_run(ptimer_state *s, int oneshot)
 {
     bool was_disabled = !s->enabled;

     assert(s->in_transaction);

     if (was_disabled && s->period == 0) {
         if (!qtest_enabled()) {
             fprintf(stderr, "Timer with period zero, disabling\n");
         }
         return;
     }
     s->enabled = oneshot ? 2 : 1;
     if (was_disabled) {
         s->need_reload = true;
     }
 }

 /* Pause a timer.  Note that this may cause it to "lose" time, even if it
    is immediately restarted.  */
 void ptimer_stop(ptimer_state *s)
 {
     assert(s->in_transaction);

     if (!s->enabled)
         return;

     s->delta = ptimer_get_count(s);
     timer_del(s->timer);
     s->enabled = 0;
     s->need_reload = false;
 }

 /* Set counter increment interval in nanoseconds.  */
 void ptimer_set_period(ptimer_state *s, int64_t period)
 {
     assert(s->in_transaction);
     s->delta = ptimer_get_count(s);
     s->period = period;
     s->period_frac = 0;
     if (s->enabled) {
         s->need_reload = true;
     }
 }

 /* Set counter increment interval from a Clock */
 void ptimer_set_period_from_clock(ptimer_state *s, const Clock *clk,
                                   unsigned int divisor)
 {
     /*
      * The raw clock period is a 64-bit value in units of 2^-32 ns;
      * put another way it's a 32.32 fixed-point ns value. Our internal
      * representation of the period is 64.32 fixed point ns, so
      * the conversion is simple.
      */
     uint64_t raw_period = clock_get(clk);
     uint64_t period_frac;

     assert(s->in_transaction);
     s->delta = ptimer_get_count(s);
     s->period = extract64(raw_period, 32, 32);
     period_frac = extract64(raw_period, 0, 32);
     /*
      * divisor specifies a possible frequency divisor between the
      * clock and the timer, so it is a multiplier on the period.
      * We do the multiply after splitting the raw period out into
      * period and frac to avoid having to do a 32*64->96 multiply.
      */
     s->period *= divisor;
     period_frac *= divisor;
     s->period += extract64(period_frac, 32, 32);
     s->period_frac = (uint32_t)period_frac;

     if (s->enabled) {
         s->need_reload = true;
     }
 }

 /* Set counter frequency in Hz.  */
 void ptimer_set_freq(ptimer_state *s, uint32_t freq)
 {
     assert(s->in_transaction);
     s->delta = ptimer_get_count(s);
     s->period = 1000000000ll / freq;
     s->period_frac = (1000000000ll << 32) / freq;
     if (s->enabled) {
         s->need_reload = true;
     }
 }

 /* Set the initial countdown value.  If reload is nonzero then also set
    count = limit.  */
 void ptimer_set_limit(ptimer_state *s, uint64_t limit, int reload)
 {
     assert(s->in_transaction);
     s->limit = limit;
     if (reload)
         s->delta = limit;
     if (s->enabled && reload) {
         s->need_reload = true;
     }
 }

 uint64_t ptimer_get_limit(ptimer_state *s)
 {
     return s->limit;
 }

 void ptimer_transaction_begin(ptimer_state *s)
 {
     assert(!s->in_transaction);
     s->in_transaction = true;
     s->need_reload = false;
 }

 void ptimer_transaction_commit(ptimer_state *s)
 {
     assert(s->in_transaction);
     /*
      * We must loop here because ptimer_reload() can call the callback
      * function, which might then update ptimer state in a way that
      * means we need to do another reload and possibly another callback.
      * A disabled timer never needs reloading (and if we don't check
      * this then we loop forever if ptimer_reload() disables the timer).
      */
     while (s->need_reload && s->enabled) {
         s->need_reload = false;
         s->next_event = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
         ptimer_reload(s, 0);
     }
     /* Now we've finished reload we can leave the transaction block. */
     s->in_transaction = false;
 }

 const VMStateDescription vmstate_ptimer = {
     .name = "ptimer",
     .version_id = 1,
     .minimum_version_id = 1,
     .fields = (VMStateField[]) {
         VMSTATE_UINT8(enabled, ptimer_state),
         VMSTATE_UINT64(limit, ptimer_state),
         VMSTATE_UINT64(delta, ptimer_state),
         VMSTATE_UINT32(period_frac, ptimer_state),
         VMSTATE_INT64(period, ptimer_state),
         VMSTATE_INT64(last_event, ptimer_state),
         VMSTATE_INT64(next_event, ptimer_state),
         VMSTATE_TIMER_PTR(timer, ptimer_state),
         VMSTATE_END_OF_LIST()
     }
 };

 ptimer_state *ptimer_init(ptimer_cb callback, void *callback_opaque,
                           uint8_t policy_mask)
 {
     ptimer_state *s;

     /* The callback function is mandatory. */
     assert(callback);

     s = g_new0(ptimer_state, 1);
     s->timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, ptimer_tick, s);
     s->policy_mask = policy_mask;
     s->callback = callback;
     s->callback_opaque = callback_opaque;

     /*
      * These two policies are incompatible -- trigger-on-decrement implies
      * a timer trigger when the count becomes 0, but no-immediate-trigger
      * implies a trigger when the count stops being 0.
      */
     assert(!((policy_mask & PTIMER_POLICY_TRIGGER_ONLY_ON_DECREMENT) &&
              (policy_mask & PTIMER_POLICY_NO_IMMEDIATE_TRIGGER)));
     return s;
 }

 void ptimer_free(ptimer_state *s)
 {
     timer_free(s->timer);
     g_free(s);
 }
	/*
	* General purpose implementation of a simple periodic countdown timer.
	*
	* Copyright (c) 2007 CodeSourcery.
	*
	* This code is licensed under the GNU LGPL.
	*/

	#include "qemu/osdep.h"
	#include "hw/ptimer.h"
	#include "migration/vmstate.h"
	#include "qemu/host-utils.h"
	#include "exec/replay-core.h"
	#include "sysemu/cpu-timers.h"
	#include "sysemu/qtest.h"
	#include "block/aio.h"
	#include "hw/clock.h"

	#define DELTA_ADJUST 1
	#define DELTA_NO_ADJUST -1

	struct ptimer_state
	{
	uint8_t enabled; /* 0 = disabled, 1 = periodic, 2 = oneshot. */
	uint64_t limit;
	uint64_t delta;
	uint32_t period_frac;
	int64_t period;
	int64_t last_event;
	int64_t next_event;
	uint8_t policy_mask;
	QEMUTimer *timer;
	ptimer_cb callback;
	void *callback_opaque;
	/*
	* These track whether we're in a transaction block, and if we
	* need to do a timer reload when the block finishes. They don't
	* need to be migrated because migration can never happen in the
	* middle of a transaction block.
	*/
	bool in_transaction;
	bool need_reload;
	};

	/* Use a bottom-half routine to avoid reentrancy issues. */
	static void ptimer_trigger(ptimer_state *s)
	{
	s->callback(s->callback_opaque);
	}

	static void ptimer_reload(ptimer_state *s, int delta_adjust)
	{
	uint32_t period_frac;
	uint64_t period;
	uint64_t delta;
	bool suppress_trigger = false;

	/*
	* Note that if delta_adjust is 0 then we must be here because of
	* a count register write or timer start, not because of timer expiry.
	* In that case the policy might require us to suppress the timer trigger
	* that we would otherwise generate for a zero delta.
	*/
	if (delta_adjust == 0 &&
	(s->policy_mask & PTIMER_POLICY_TRIGGER_ONLY_ON_DECREMENT)) {
	suppress_trigger = true;
	}
	if (s->delta == 0 && !(s->policy_mask & PTIMER_POLICY_NO_IMMEDIATE_TRIGGER)
	&& !suppress_trigger) {
	ptimer_trigger(s);
	}

	/*
	* Note that ptimer_trigger() might call the device callback function,
	* which can then modify timer state, so we must not cache any fields
	* from ptimer_state until after we have called it.
	*/
	delta = s->delta;
	period = s->period;
	period_frac = s->period_frac;

	if (delta == 0 && !(s->policy_mask & PTIMER_POLICY_NO_IMMEDIATE_RELOAD)) {
	delta = s->delta = s->limit;
	}

	if (s->period == 0) {
	if (!qtest_enabled()) {
	fprintf(stderr, "Timer with period zero, disabling\n");
	}
	timer_del(s->timer);
	s->enabled = 0;
	return;
	}

	if (s->policy_mask & PTIMER_POLICY_WRAP_AFTER_ONE_PERIOD) {
	if (delta_adjust != DELTA_NO_ADJUST) {
	delta += delta_adjust;
	}
	}

	if (delta == 0 && (s->policy_mask & PTIMER_POLICY_CONTINUOUS_TRIGGER)) {
	if (s->enabled == 1 && s->limit == 0) {
	delta = 1;
	}
	}

	if (delta == 0 && (s->policy_mask & PTIMER_POLICY_NO_IMMEDIATE_TRIGGER)) {
	if (delta_adjust != DELTA_NO_ADJUST) {
	delta = 1;
	}
	}

	if (delta == 0 && (s->policy_mask & PTIMER_POLICY_NO_IMMEDIATE_RELOAD)) {
	if (s->enabled == 1 && s->limit != 0) {
	delta = 1;
	}
	}

	if (delta == 0) {
	if (s->enabled == 0) {
	/* trigger callback disabled the timer already */
	return;
	}
	if (!qtest_enabled()) {
	fprintf(stderr, "Timer with delta zero, disabling\n");
	}
	timer_del(s->timer);
	s->enabled = 0;
	return;
	}

	/*
	* Artificially limit timeout rate to something
	* achievable under QEMU. Otherwise, QEMU spends all
	* its time generating timer interrupts, and there
	* is no forward progress.
	* About ten microseconds is the fastest that really works
	* on the current generation of host machines.
	*/

	if (s->enabled == 1 && (delta * period < 10000) &&
	!icount_enabled() && !qtest_enabled()) {
	period = 10000 / delta;
	period_frac = 0;
	}

	s->last_event = s->next_event;
	s->next_event = s->last_event + delta * period;
	if (period_frac) {
	s->next_event += ((int64_t)period_frac * delta) >> 32;
	}
	timer_mod(s->timer, s->next_event);
	}

	static void ptimer_tick(void *opaque)
	{
	ptimer_state s = (ptimer_state )opaque;
	bool trigger = true;

	/*
	* We perform all the tick actions within a begin/commit block
	* because the callback function that ptimer_trigger() calls
	* might make calls into the ptimer APIs that provoke another
	* trigger, and we want that to cause the callback function
	* to be called iteratively, not recursively.
	*/
	ptimer_transaction_begin(s);

	if (s->enabled == 2) {
	s->delta = 0;
	s->enabled = 0;
	} else {
	int delta_adjust = DELTA_ADJUST;

	if (s->delta == 0 \|\| s->limit == 0) {
	/* If a "continuous trigger" policy is not used and limit == 0,
	we should error out. delta == 0 means that this tick is
	caused by a "no immediate reload" policy, so it shouldn't
	be adjusted. */
	delta_adjust = DELTA_NO_ADJUST;
	}

	if (!(s->policy_mask & PTIMER_POLICY_NO_IMMEDIATE_TRIGGER)) {
	/* Avoid re-trigger on deferred reload if "no immediate trigger"
	policy isn't used. */
	trigger = (delta_adjust == DELTA_ADJUST);
	}

	s->delta = s->limit;

	ptimer_reload(s, delta_adjust);
	}

	if (trigger) {
	ptimer_trigger(s);
	}

	ptimer_transaction_commit(s);
	}

	uint64_t ptimer_get_count(ptimer_state *s)
	{
	uint64_t counter;

	if (s->enabled && s->delta != 0) {
	int64_t now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
	int64_t next = s->next_event;
	int64_t last = s->last_event;
	bool expired = (now - next >= 0);
	bool oneshot = (s->enabled == 2);

	/* Figure out the current counter value. */
	if (expired) {
	/* Prevent timer underflowing if it should already have
	triggered. */
	counter = 0;
	} else {
	uint64_t rem;
	uint64_t div;
	int clz1, clz2;
	int shift;
	uint32_t period_frac = s->period_frac;
	uint64_t period = s->period;

	if (!oneshot && (s->delta * period < 10000) &&
	!icount_enabled() && !qtest_enabled()) {
	period = 10000 / s->delta;
	period_frac = 0;
	}

	/* We need to divide time by period, where time is stored in
	rem (64-bit integer) and period is stored in period/period_frac
	(64.32 fixed point).

	Doing full precision division is hard, so scale values and
	do a 64-bit division. The result should be rounded down,
	so that the rounding error never causes the timer to go
	backwards.
	*/

	rem = next - now;
	div = period;

	clz1 = clz64(rem);
	clz2 = clz64(div);
	shift = clz1 < clz2 ? clz1 : clz2;

	rem <<= shift;
	div <<= shift;
	if (shift >= 32) {
	div \|= ((uint64_t)period_frac << (shift - 32));
	} else {
	if (shift != 0)
	div \|= (period_frac >> (32 - shift));
	/* Look at remaining bits of period_frac and round div up if
	necessary. */
	if ((uint32_t)(period_frac << shift))
	div += 1;
	}
	counter = rem / div;

	if (s->policy_mask & PTIMER_POLICY_WRAP_AFTER_ONE_PERIOD) {
	/* Before wrapping around, timer should stay with counter = 0
	for a one period. */
	if (!oneshot && s->delta == s->limit) {
	if (now == last) {
	/* Counter == delta here, check whether it was
	adjusted and if it was, then right now it is
	that "one period". */
	if (counter == s->limit + DELTA_ADJUST) {
	return 0;
	}
	} else if (counter == s->limit) {
	/* Since the counter is rounded down and now != last,
	the counter == limit means that delta was adjusted
	by +1 and right now it is that adjusted period. */
	return 0;
	}
	}
	}
	}

	if (s->policy_mask & PTIMER_POLICY_NO_COUNTER_ROUND_DOWN) {
	/* If now == last then delta == limit, i.e. the counter already
	represents the correct value. It would be rounded down a 1ns
	later. */
	if (now != last) {
	counter += 1;
	}
	}
	} else {
	counter = s->delta;
	}
	return counter;
	}

	void ptimer_set_count(ptimer_state *s, uint64_t count)
	{
	assert(s->in_transaction);
	s->delta = count;
	if (s->enabled) {
	s->need_reload = true;
	}
	}

	void ptimer_run(ptimer_state *s, int oneshot)
	{
	bool was_disabled = !s->enabled;

	assert(s->in_transaction);

	if (was_disabled && s->period == 0) {
	if (!qtest_enabled()) {
	fprintf(stderr, "Timer with period zero, disabling\n");
	}
	return;
	}
	s->enabled = oneshot ? 2 : 1;
	if (was_disabled) {
	s->need_reload = true;
	}
	}

	/* Pause a timer. Note that this may cause it to "lose" time, even if it
	is immediately restarted. */
	void ptimer_stop(ptimer_state *s)
	{
	assert(s->in_transaction);

	if (!s->enabled)
	return;

	s->delta = ptimer_get_count(s);
	timer_del(s->timer);
	s->enabled = 0;
	s->need_reload = false;
	}

	/* Set counter increment interval in nanoseconds. */
	void ptimer_set_period(ptimer_state *s, int64_t period)
	{
	assert(s->in_transaction);
	s->delta = ptimer_get_count(s);
	s->period = period;
	s->period_frac = 0;
	if (s->enabled) {
	s->need_reload = true;
	}
	}

	/* Set counter increment interval from a Clock */
	void ptimer_set_period_from_clock(ptimer_state s, const Clock clk,
	unsigned int divisor)
	{
	/*
	* The raw clock period is a 64-bit value in units of 2^-32 ns;
	* put another way it's a 32.32 fixed-point ns value. Our internal
	* representation of the period is 64.32 fixed point ns, so
	* the conversion is simple.
	*/
	uint64_t raw_period = clock_get(clk);
	uint64_t period_frac;

	assert(s->in_transaction);
	s->delta = ptimer_get_count(s);
	s->period = extract64(raw_period, 32, 32);
	period_frac = extract64(raw_period, 0, 32);
	/*
	* divisor specifies a possible frequency divisor between the
	* clock and the timer, so it is a multiplier on the period.
	* We do the multiply after splitting the raw period out into
	* period and frac to avoid having to do a 32*64->96 multiply.
	*/
	s->period *= divisor;
	period_frac *= divisor;
	s->period += extract64(period_frac, 32, 32);
	s->period_frac = (uint32_t)period_frac;

	if (s->enabled) {
	s->need_reload = true;
	}
	}

	/* Set counter frequency in Hz. */
	void ptimer_set_freq(ptimer_state *s, uint32_t freq)
	{
	assert(s->in_transaction);
	s->delta = ptimer_get_count(s);
	s->period = 1000000000ll / freq;
	s->period_frac = (1000000000ll << 32) / freq;
	if (s->enabled) {
	s->need_reload = true;
	}
	}

	/* Set the initial countdown value. If reload is nonzero then also set
	count = limit. */
	void ptimer_set_limit(ptimer_state *s, uint64_t limit, int reload)
	{
	assert(s->in_transaction);
	s->limit = limit;
	if (reload)
	s->delta = limit;
	if (s->enabled && reload) {
	s->need_reload = true;
	}
	}

	uint64_t ptimer_get_limit(ptimer_state *s)
	{
	return s->limit;
	}

	void ptimer_transaction_begin(ptimer_state *s)
	{
	assert(!s->in_transaction);
	s->in_transaction = true;
	s->need_reload = false;
	}

	void ptimer_transaction_commit(ptimer_state *s)
	{
	assert(s->in_transaction);
	/*
	* We must loop here because ptimer_reload() can call the callback
	* function, which might then update ptimer state in a way that
	* means we need to do another reload and possibly another callback.
	* A disabled timer never needs reloading (and if we don't check
	* this then we loop forever if ptimer_reload() disables the timer).
	*/
	while (s->need_reload && s->enabled) {
	s->need_reload = false;
	s->next_event = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
	ptimer_reload(s, 0);
	}
	/* Now we've finished reload we can leave the transaction block. */
	s->in_transaction = false;
	}

	const VMStateDescription vmstate_ptimer = {
	.name = "ptimer",
	.version_id = 1,
	.minimum_version_id = 1,
	.fields = (VMStateField[]) {
	VMSTATE_UINT8(enabled, ptimer_state),
	VMSTATE_UINT64(limit, ptimer_state),
	VMSTATE_UINT64(delta, ptimer_state),
	VMSTATE_UINT32(period_frac, ptimer_state),
	VMSTATE_INT64(period, ptimer_state),
	VMSTATE_INT64(last_event, ptimer_state),
	VMSTATE_INT64(next_event, ptimer_state),
	VMSTATE_TIMER_PTR(timer, ptimer_state),
	VMSTATE_END_OF_LIST()
	}
	};

	ptimer_state ptimer_init(ptimer_cb callback, void callback_opaque,
	uint8_t policy_mask)
	{
	ptimer_state *s;

	/* The callback function is mandatory. */
	assert(callback);

	s = g_new0(ptimer_state, 1);
	s->timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, ptimer_tick, s);
	s->policy_mask = policy_mask;
	s->callback = callback;
	s->callback_opaque = callback_opaque;

	/*
	* These two policies are incompatible -- trigger-on-decrement implies
	* a timer trigger when the count becomes 0, but no-immediate-trigger
	* implies a trigger when the count stops being 0.
	*/
	assert(!((policy_mask & PTIMER_POLICY_TRIGGER_ONLY_ON_DECREMENT) &&
	(policy_mask & PTIMER_POLICY_NO_IMMEDIATE_TRIGGER)));
	return s;
	}

	void ptimer_free(ptimer_state *s)
	{
	timer_free(s->timer);
	g_free(s);
	}