hw/slavio_timer.c - qemu - Git at Google

 /*
  * QEMU Sparc SLAVIO timer controller emulation
  *
  * Copyright (c) 2003-2005 Fabrice Bellard
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
  * in the Software without restriction, including without limitation the rights
  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  * copies of the Software, and to permit persons to whom the Software is
  * furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in
  * all copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */

 #include "sun4m.h"
 #include "qemu-timer.h"
 #include "sysbus.h"

 //#define DEBUG_TIMER

 #ifdef DEBUG_TIMER
 #define DPRINTF(fmt, ...)                                       \
     do { printf("TIMER: " fmt , ## __VA_ARGS__); } while (0)
 #else
 #define DPRINTF(fmt, ...) do {} while (0)
 #endif

 /*
  * Registers of hardware timer in sun4m.
  *
  * This is the timer/counter part of chip STP2001 (Slave I/O), also
  * produced as NCR89C105. See
  * http://www.ibiblio.org/pub/historic-linux/early-ports/Sparc/NCR/NCR89C105.txt
  *
  * The 31-bit counter is incremented every 500ns by bit 9. Bits 8..0
  * are zero. Bit 31 is 1 when count has been reached.
  *
  * Per-CPU timers interrupt local CPU, system timer uses normal
  * interrupt routing.
  *
  */

 #define MAX_CPUS 16

 typedef struct CPUTimerState {
     qemu_irq irq;
     ptimer_state *timer;
     uint32_t count, counthigh, reached;
     uint64_t limit;
     // processor only
     uint32_t running;
 } CPUTimerState;

 typedef struct SLAVIO_TIMERState {
     SysBusDevice busdev;
     uint32_t num_cpus;
     CPUTimerState cputimer[MAX_CPUS + 1];
     uint32_t cputimer_mode;
 } SLAVIO_TIMERState;

 typedef struct TimerContext {
     SLAVIO_TIMERState *s;
     unsigned int timer_index; /* 0 for system, 1 ... MAX_CPUS for CPU timers */
 } TimerContext;

 #define SYS_TIMER_SIZE 0x14
 #define CPU_TIMER_SIZE 0x10

 #define TIMER_LIMIT         0
 #define TIMER_COUNTER       1
 #define TIMER_COUNTER_NORST 2
 #define TIMER_STATUS        3
 #define TIMER_MODE          4

 #define TIMER_COUNT_MASK32 0xfffffe00
 #define TIMER_LIMIT_MASK32 0x7fffffff
 #define TIMER_MAX_COUNT64  0x7ffffffffffffe00ULL
 #define TIMER_MAX_COUNT32  0x7ffffe00ULL
 #define TIMER_REACHED      0x80000000
 #define TIMER_PERIOD       500ULL // 500ns
 #define LIMIT_TO_PERIODS(l) ((l) >> 9)
 #define PERIODS_TO_LIMIT(l) ((l) << 9)

 static int slavio_timer_is_user(TimerContext *tc)
 {
     SLAVIO_TIMERState *s = tc->s;
     unsigned int timer_index = tc->timer_index;

     return timer_index != 0 && (s->cputimer_mode & (1 << (timer_index - 1)));
 }

 // Update count, set irq, update expire_time
 // Convert from ptimer countdown units
 static void slavio_timer_get_out(CPUTimerState *t)
 {
     uint64_t count, limit;

     if (t->limit == 0) { /* free-run system or processor counter */
         limit = TIMER_MAX_COUNT32;
     } else {
         limit = t->limit;
     }
     count = limit - PERIODS_TO_LIMIT(ptimer_get_count(t->timer));

     DPRINTF("get_out: limit %" PRIx64 " count %x%08x\n", t->limit, t->counthigh,
             t->count);
     t->count = count & TIMER_COUNT_MASK32;
     t->counthigh = count >> 32;
 }

 // timer callback
 static void slavio_timer_irq(void *opaque)
 {
     TimerContext *tc = opaque;
     SLAVIO_TIMERState *s = tc->s;
     CPUTimerState *t = &s->cputimer[tc->timer_index];

     slavio_timer_get_out(t);
     DPRINTF("callback: count %x%08x\n", t->counthigh, t->count);
     t->reached = TIMER_REACHED;
     if (!slavio_timer_is_user(tc)) {
         qemu_irq_raise(t->irq);
     }
 }

 static uint32_t slavio_timer_mem_readl(void *opaque, target_phys_addr_t addr)
 {
     TimerContext *tc = opaque;
     SLAVIO_TIMERState *s = tc->s;
     uint32_t saddr, ret;
     unsigned int timer_index = tc->timer_index;
     CPUTimerState *t = &s->cputimer[timer_index];

     saddr = addr >> 2;
     switch (saddr) {
     case TIMER_LIMIT:
         // read limit (system counter mode) or read most signifying
         // part of counter (user mode)
         if (slavio_timer_is_user(tc)) {
             // read user timer MSW
             slavio_timer_get_out(t);
             ret = t->counthigh | t->reached;
         } else {
             // read limit
             // clear irq
             qemu_irq_lower(t->irq);
             t->reached = 0;
             ret = t->limit & TIMER_LIMIT_MASK32;
         }
         break;
     case TIMER_COUNTER:
         // read counter and reached bit (system mode) or read lsbits
         // of counter (user mode)
         slavio_timer_get_out(t);
         if (slavio_timer_is_user(tc)) { // read user timer LSW
             ret = t->count & TIMER_MAX_COUNT64;
         } else { // read limit
             ret = (t->count & TIMER_MAX_COUNT32) |
                 t->reached;
         }
         break;
     case TIMER_STATUS:
         // only available in processor counter/timer
         // read start/stop status
         if (timer_index > 0) {
             ret = t->running;
         } else {
             ret = 0;
         }
         break;
     case TIMER_MODE:
         // only available in system counter
         // read user/system mode
         ret = s->cputimer_mode;
         break;
     default:
         DPRINTF("invalid read address " TARGET_FMT_plx "\n", addr);
         ret = 0;
         break;
     }
     DPRINTF("read " TARGET_FMT_plx " = %08x\n", addr, ret);

     return ret;
 }

 static void slavio_timer_mem_writel(void *opaque, target_phys_addr_t addr,
                                     uint32_t val)
 {
     TimerContext *tc = opaque;
     SLAVIO_TIMERState *s = tc->s;
     uint32_t saddr;
     unsigned int timer_index = tc->timer_index;
     CPUTimerState *t = &s->cputimer[timer_index];

     DPRINTF("write " TARGET_FMT_plx " %08x\n", addr, val);
     saddr = addr >> 2;
     switch (saddr) {
     case TIMER_LIMIT:
         if (slavio_timer_is_user(tc)) {
             uint64_t count;

             // set user counter MSW, reset counter
             t->limit = TIMER_MAX_COUNT64;
             t->counthigh = val & (TIMER_MAX_COUNT64 >> 32);
             t->reached = 0;
             count = ((uint64_t)t->counthigh << 32) | t->count;
             DPRINTF("processor %d user timer set to %016" PRIx64 "\n",
                     timer_index, count);
             ptimer_set_count(t->timer, LIMIT_TO_PERIODS(t->limit - count));
         } else {
             // set limit, reset counter
             qemu_irq_lower(t->irq);
             t->limit = val & TIMER_MAX_COUNT32;
             if (t->timer) {
                 if (t->limit == 0) { /* free-run */
                     ptimer_set_limit(t->timer,
                                      LIMIT_TO_PERIODS(TIMER_MAX_COUNT32), 1);
                 } else {
                     ptimer_set_limit(t->timer, LIMIT_TO_PERIODS(t->limit), 1);
                 }
             }
         }
         break;
     case TIMER_COUNTER:
         if (slavio_timer_is_user(tc)) {
             uint64_t count;

             // set user counter LSW, reset counter
             t->limit = TIMER_MAX_COUNT64;
             t->count = val & TIMER_MAX_COUNT64;
             t->reached = 0;
             count = ((uint64_t)t->counthigh) << 32 | t->count;
             DPRINTF("processor %d user timer set to %016" PRIx64 "\n",
                     timer_index, count);
             ptimer_set_count(t->timer, LIMIT_TO_PERIODS(t->limit - count));
         } else
             DPRINTF("not user timer\n");
         break;
     case TIMER_COUNTER_NORST:
         // set limit without resetting counter
         t->limit = val & TIMER_MAX_COUNT32;
         if (t->limit == 0) { /* free-run */
             ptimer_set_limit(t->timer, LIMIT_TO_PERIODS(TIMER_MAX_COUNT32), 0);
         } else {
             ptimer_set_limit(t->timer, LIMIT_TO_PERIODS(t->limit), 0);
         }
         break;
     case TIMER_STATUS:
         if (slavio_timer_is_user(tc)) {
             // start/stop user counter
             if ((val & 1) && !t->running) {
                 DPRINTF("processor %d user timer started\n",
                         timer_index);
                 ptimer_run(t->timer, 0);
                 t->running = 1;
             } else if (!(val & 1) && t->running) {
                 DPRINTF("processor %d user timer stopped\n",
                         timer_index);
                 ptimer_stop(t->timer);
                 t->running = 0;
             }
         }
         break;
     case TIMER_MODE:
         if (timer_index == 0) {
             unsigned int i;

             for (i = 0; i < s->num_cpus; i++) {
                 unsigned int processor = 1 << i;
                 CPUTimerState *curr_timer = &s->cputimer[i + 1];

                 // check for a change in timer mode for this processor
                 if ((val & processor) != (s->cputimer_mode & processor)) {
                     if (val & processor) { // counter -> user timer
                         qemu_irq_lower(curr_timer->irq);
                         // counters are always running
                         ptimer_stop(curr_timer->timer);
                         curr_timer->running = 0;
                         // user timer limit is always the same
                         curr_timer->limit = TIMER_MAX_COUNT64;
                         ptimer_set_limit(curr_timer->timer,
                                          LIMIT_TO_PERIODS(curr_timer->limit),
                                          1);
                         // set this processors user timer bit in config
                         // register
                         s->cputimer_mode |= processor;
                         DPRINTF("processor %d changed from counter to user "
                                 "timer\n", timer_index);
                     } else { // user timer -> counter
                         // stop the user timer if it is running
                         if (curr_timer->running) {
                             ptimer_stop(curr_timer->timer);
                         }
                         // start the counter
                         ptimer_run(curr_timer->timer, 0);
                         curr_timer->running = 1;
                         // clear this processors user timer bit in config
                         // register
                         s->cputimer_mode &= ~processor;
                         DPRINTF("processor %d changed from user timer to "
                                 "counter\n", timer_index);
                     }
                 }
             }
         } else {
             DPRINTF("not system timer\n");
         }
         break;
     default:
         DPRINTF("invalid write address " TARGET_FMT_plx "\n", addr);
         break;
     }
 }

 static CPUReadMemoryFunc * const slavio_timer_mem_read[3] = {
     NULL,
     NULL,
     slavio_timer_mem_readl,
 };

 static CPUWriteMemoryFunc * const slavio_timer_mem_write[3] = {
     NULL,
     NULL,
     slavio_timer_mem_writel,
 };

 static const VMStateDescription vmstate_timer = {
     .name ="timer",
     .version_id = 3,
     .minimum_version_id = 3,
     .minimum_version_id_old = 3,
     .fields      = (VMStateField []) {
         VMSTATE_UINT64(limit, CPUTimerState),
         VMSTATE_UINT32(count, CPUTimerState),
         VMSTATE_UINT32(counthigh, CPUTimerState),
         VMSTATE_UINT32(reached, CPUTimerState),
         VMSTATE_UINT32(running, CPUTimerState),
         VMSTATE_PTIMER(timer, CPUTimerState),
         VMSTATE_END_OF_LIST()
     }
 };

 static const VMStateDescription vmstate_slavio_timer = {
     .name ="slavio_timer",
     .version_id = 3,
     .minimum_version_id = 3,
     .minimum_version_id_old = 3,
     .fields      = (VMStateField []) {
         VMSTATE_STRUCT_ARRAY(cputimer, SLAVIO_TIMERState, MAX_CPUS + 1, 3,
                              vmstate_timer, CPUTimerState),
         VMSTATE_END_OF_LIST()
     }
 };

 static void slavio_timer_reset(DeviceState *d)
 {
     SLAVIO_TIMERState *s = container_of(d, SLAVIO_TIMERState, busdev.qdev);
     unsigned int i;
     CPUTimerState *curr_timer;

     for (i = 0; i <= MAX_CPUS; i++) {
         curr_timer = &s->cputimer[i];
         curr_timer->limit = 0;
         curr_timer->count = 0;
         curr_timer->reached = 0;
         if (i < s->num_cpus) {
             ptimer_set_limit(curr_timer->timer,
                              LIMIT_TO_PERIODS(TIMER_MAX_COUNT32), 1);
             ptimer_run(curr_timer->timer, 0);
         }
         curr_timer->running = 1;
     }
     s->cputimer_mode = 0;
 }

 static int slavio_timer_init1(SysBusDevice *dev)
 {
     int io;
     SLAVIO_TIMERState *s = FROM_SYSBUS(SLAVIO_TIMERState, dev);
     QEMUBH *bh;
     unsigned int i;
     TimerContext *tc;

     for (i = 0; i <= MAX_CPUS; i++) {
         tc = qemu_mallocz(sizeof(TimerContext));
         tc->s = s;
         tc->timer_index = i;

         bh = qemu_bh_new(slavio_timer_irq, tc);
         s->cputimer[i].timer = ptimer_init(bh);
         ptimer_set_period(s->cputimer[i].timer, TIMER_PERIOD);

         io = cpu_register_io_memory(slavio_timer_mem_read,
                                     slavio_timer_mem_write, tc);
         if (i == 0) {
             sysbus_init_mmio(dev, SYS_TIMER_SIZE, io);
         } else {
             sysbus_init_mmio(dev, CPU_TIMER_SIZE, io);
         }

         sysbus_init_irq(dev, &s->cputimer[i].irq);
     }

     return 0;
 }

 static SysBusDeviceInfo slavio_timer_info = {
     .init = slavio_timer_init1,
     .qdev.name  = "slavio_timer",
     .qdev.size  = sizeof(SLAVIO_TIMERState),
     .qdev.vmsd  = &vmstate_slavio_timer,
     .qdev.reset = slavio_timer_reset,
     .qdev.props = (Property[]) {
         DEFINE_PROP_UINT32("num_cpus",  SLAVIO_TIMERState, num_cpus,  0),
         DEFINE_PROP_END_OF_LIST(),
     }
 };

 static void slavio_timer_register_devices(void)
 {
     sysbus_register_withprop(&slavio_timer_info);
 }

 device_init(slavio_timer_register_devices)
	/*
	* QEMU Sparc SLAVIO timer controller emulation
	*
	* Copyright (c) 2003-2005 Fabrice Bellard
	*
	* Permission is hereby granted, free of charge, to any person obtaining a copy
	* of this software and associated documentation files (the "Software"), to deal
	* in the Software without restriction, including without limitation the rights
	* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	* copies of the Software, and to permit persons to whom the Software is
	* furnished to do so, subject to the following conditions:
	*
	* The above copyright notice and this permission notice shall be included in
	* all copies or substantial portions of the Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
	* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
	* THE SOFTWARE.
	*/

	#include "sun4m.h"
	#include "qemu-timer.h"
	#include "sysbus.h"

	//#define DEBUG_TIMER

	#ifdef DEBUG_TIMER
	#define DPRINTF(fmt, ...) \
	do { printf("TIMER: " fmt , ## __VA_ARGS__); } while (0)
	#else
	#define DPRINTF(fmt, ...) do {} while (0)
	#endif

	/*
	* Registers of hardware timer in sun4m.
	*
	* This is the timer/counter part of chip STP2001 (Slave I/O), also
	* produced as NCR89C105. See
	* http://www.ibiblio.org/pub/historic-linux/early-ports/Sparc/NCR/NCR89C105.txt
	*
	* The 31-bit counter is incremented every 500ns by bit 9. Bits 8..0
	* are zero. Bit 31 is 1 when count has been reached.
	*
	* Per-CPU timers interrupt local CPU, system timer uses normal
	* interrupt routing.
	*
	*/

	#define MAX_CPUS 16

	typedef struct CPUTimerState {
	qemu_irq irq;
	ptimer_state *timer;
	uint32_t count, counthigh, reached;
	uint64_t limit;
	// processor only
	uint32_t running;
	} CPUTimerState;

	typedef struct SLAVIO_TIMERState {
	SysBusDevice busdev;
	uint32_t num_cpus;
	CPUTimerState cputimer[MAX_CPUS + 1];
	uint32_t cputimer_mode;
	} SLAVIO_TIMERState;

	typedef struct TimerContext {
	SLAVIO_TIMERState *s;
	unsigned int timer_index; /* 0 for system, 1 ... MAX_CPUS for CPU timers */
	} TimerContext;

	#define SYS_TIMER_SIZE 0x14
	#define CPU_TIMER_SIZE 0x10

	#define TIMER_LIMIT 0
	#define TIMER_COUNTER 1
	#define TIMER_COUNTER_NORST 2
	#define TIMER_STATUS 3
	#define TIMER_MODE 4

	#define TIMER_COUNT_MASK32 0xfffffe00
	#define TIMER_LIMIT_MASK32 0x7fffffff
	#define TIMER_MAX_COUNT64 0x7ffffffffffffe00ULL
	#define TIMER_MAX_COUNT32 0x7ffffe00ULL
	#define TIMER_REACHED 0x80000000
	#define TIMER_PERIOD 500ULL // 500ns
	#define LIMIT_TO_PERIODS(l) ((l) >> 9)
	#define PERIODS_TO_LIMIT(l) ((l) << 9)

	static int slavio_timer_is_user(TimerContext *tc)
	{
	SLAVIO_TIMERState *s = tc->s;
	unsigned int timer_index = tc->timer_index;

	return timer_index != 0 && (s->cputimer_mode & (1 << (timer_index - 1)));
	}

	// Update count, set irq, update expire_time
	// Convert from ptimer countdown units
	static void slavio_timer_get_out(CPUTimerState *t)
	{
	uint64_t count, limit;

	if (t->limit == 0) { /* free-run system or processor counter */
	limit = TIMER_MAX_COUNT32;
	} else {
	limit = t->limit;
	}
	count = limit - PERIODS_TO_LIMIT(ptimer_get_count(t->timer));

	DPRINTF("get_out: limit %" PRIx64 " count %x%08x\n", t->limit, t->counthigh,
	t->count);
	t->count = count & TIMER_COUNT_MASK32;
	t->counthigh = count >> 32;
	}

	// timer callback
	static void slavio_timer_irq(void *opaque)
	{
	TimerContext *tc = opaque;
	SLAVIO_TIMERState *s = tc->s;
	CPUTimerState *t = &s->cputimer[tc->timer_index];

	slavio_timer_get_out(t);
	DPRINTF("callback: count %x%08x\n", t->counthigh, t->count);
	t->reached = TIMER_REACHED;
	if (!slavio_timer_is_user(tc)) {
	qemu_irq_raise(t->irq);
	}
	}

	static uint32_t slavio_timer_mem_readl(void *opaque, target_phys_addr_t addr)
	{
	TimerContext *tc = opaque;
	SLAVIO_TIMERState *s = tc->s;
	uint32_t saddr, ret;
	unsigned int timer_index = tc->timer_index;
	CPUTimerState *t = &s->cputimer[timer_index];

	saddr = addr >> 2;
	switch (saddr) {
	case TIMER_LIMIT:
	// read limit (system counter mode) or read most signifying
	// part of counter (user mode)
	if (slavio_timer_is_user(tc)) {
	// read user timer MSW
	slavio_timer_get_out(t);
	ret = t->counthigh \| t->reached;
	} else {
	// read limit
	// clear irq
	qemu_irq_lower(t->irq);
	t->reached = 0;
	ret = t->limit & TIMER_LIMIT_MASK32;
	}
	break;
	case TIMER_COUNTER:
	// read counter and reached bit (system mode) or read lsbits
	// of counter (user mode)
	slavio_timer_get_out(t);
	if (slavio_timer_is_user(tc)) { // read user timer LSW
	ret = t->count & TIMER_MAX_COUNT64;
	} else { // read limit
	ret = (t->count & TIMER_MAX_COUNT32) \|
	t->reached;
	}
	break;
	case TIMER_STATUS:
	// only available in processor counter/timer
	// read start/stop status
	if (timer_index > 0) {
	ret = t->running;
	} else {
	ret = 0;
	}
	break;
	case TIMER_MODE:
	// only available in system counter
	// read user/system mode
	ret = s->cputimer_mode;
	break;
	default:
	DPRINTF("invalid read address " TARGET_FMT_plx "\n", addr);
	ret = 0;
	break;
	}
	DPRINTF("read " TARGET_FMT_plx " = %08x\n", addr, ret);

	return ret;
	}

	static void slavio_timer_mem_writel(void *opaque, target_phys_addr_t addr,
	uint32_t val)
	{
	TimerContext *tc = opaque;
	SLAVIO_TIMERState *s = tc->s;
	uint32_t saddr;
	unsigned int timer_index = tc->timer_index;
	CPUTimerState *t = &s->cputimer[timer_index];

	DPRINTF("write " TARGET_FMT_plx " %08x\n", addr, val);
	saddr = addr >> 2;
	switch (saddr) {
	case TIMER_LIMIT:
	if (slavio_timer_is_user(tc)) {
	uint64_t count;

	// set user counter MSW, reset counter
	t->limit = TIMER_MAX_COUNT64;
	t->counthigh = val & (TIMER_MAX_COUNT64 >> 32);
	t->reached = 0;
	count = ((uint64_t)t->counthigh << 32) \| t->count;
	DPRINTF("processor %d user timer set to %016" PRIx64 "\n",
	timer_index, count);
	ptimer_set_count(t->timer, LIMIT_TO_PERIODS(t->limit - count));
	} else {
	// set limit, reset counter
	qemu_irq_lower(t->irq);
	t->limit = val & TIMER_MAX_COUNT32;
	if (t->timer) {
	if (t->limit == 0) { /* free-run */
	ptimer_set_limit(t->timer,
	LIMIT_TO_PERIODS(TIMER_MAX_COUNT32), 1);
	} else {
	ptimer_set_limit(t->timer, LIMIT_TO_PERIODS(t->limit), 1);
	}
	}
	}
	break;
	case TIMER_COUNTER:
	if (slavio_timer_is_user(tc)) {
	uint64_t count;

	// set user counter LSW, reset counter
	t->limit = TIMER_MAX_COUNT64;
	t->count = val & TIMER_MAX_COUNT64;
	t->reached = 0;
	count = ((uint64_t)t->counthigh) << 32 \| t->count;
	DPRINTF("processor %d user timer set to %016" PRIx64 "\n",
	timer_index, count);
	ptimer_set_count(t->timer, LIMIT_TO_PERIODS(t->limit - count));
	} else
	DPRINTF("not user timer\n");
	break;
	case TIMER_COUNTER_NORST:
	// set limit without resetting counter
	t->limit = val & TIMER_MAX_COUNT32;
	if (t->limit == 0) { /* free-run */
	ptimer_set_limit(t->timer, LIMIT_TO_PERIODS(TIMER_MAX_COUNT32), 0);
	} else {
	ptimer_set_limit(t->timer, LIMIT_TO_PERIODS(t->limit), 0);
	}
	break;
	case TIMER_STATUS:
	if (slavio_timer_is_user(tc)) {
	// start/stop user counter
	if ((val & 1) && !t->running) {
	DPRINTF("processor %d user timer started\n",
	timer_index);
	ptimer_run(t->timer, 0);
	t->running = 1;
	} else if (!(val & 1) && t->running) {
	DPRINTF("processor %d user timer stopped\n",
	timer_index);
	ptimer_stop(t->timer);
	t->running = 0;
	}
	}
	break;
	case TIMER_MODE:
	if (timer_index == 0) {
	unsigned int i;

	for (i = 0; i < s->num_cpus; i++) {
	unsigned int processor = 1 << i;
	CPUTimerState *curr_timer = &s->cputimer[i + 1];

	// check for a change in timer mode for this processor
	if ((val & processor) != (s->cputimer_mode & processor)) {
	if (val & processor) { // counter -> user timer
	qemu_irq_lower(curr_timer->irq);
	// counters are always running
	ptimer_stop(curr_timer->timer);
	curr_timer->running = 0;
	// user timer limit is always the same
	curr_timer->limit = TIMER_MAX_COUNT64;
	ptimer_set_limit(curr_timer->timer,
	LIMIT_TO_PERIODS(curr_timer->limit),
	1);
	// set this processors user timer bit in config
	// register
	s->cputimer_mode \|= processor;
	DPRINTF("processor %d changed from counter to user "
	"timer\n", timer_index);
	} else { // user timer -> counter
	// stop the user timer if it is running
	if (curr_timer->running) {
	ptimer_stop(curr_timer->timer);
	}
	// start the counter
	ptimer_run(curr_timer->timer, 0);
	curr_timer->running = 1;
	// clear this processors user timer bit in config
	// register
	s->cputimer_mode &= ~processor;
	DPRINTF("processor %d changed from user timer to "
	"counter\n", timer_index);
	}
	}
	}
	} else {
	DPRINTF("not system timer\n");
	}
	break;
	default:
	DPRINTF("invalid write address " TARGET_FMT_plx "\n", addr);
	break;
	}
	}

	static CPUReadMemoryFunc * const slavio_timer_mem_read[3] = {
	NULL,
	NULL,
	slavio_timer_mem_readl,
	};

	static CPUWriteMemoryFunc * const slavio_timer_mem_write[3] = {
	NULL,
	NULL,
	slavio_timer_mem_writel,
	};

	static const VMStateDescription vmstate_timer = {
	.name ="timer",
	.version_id = 3,
	.minimum_version_id = 3,
	.minimum_version_id_old = 3,
	.fields = (VMStateField []) {
	VMSTATE_UINT64(limit, CPUTimerState),
	VMSTATE_UINT32(count, CPUTimerState),
	VMSTATE_UINT32(counthigh, CPUTimerState),
	VMSTATE_UINT32(reached, CPUTimerState),
	VMSTATE_UINT32(running, CPUTimerState),
	VMSTATE_PTIMER(timer, CPUTimerState),
	VMSTATE_END_OF_LIST()
	}
	};

	static const VMStateDescription vmstate_slavio_timer = {
	.name ="slavio_timer",
	.version_id = 3,
	.minimum_version_id = 3,
	.minimum_version_id_old = 3,
	.fields = (VMStateField []) {
	VMSTATE_STRUCT_ARRAY(cputimer, SLAVIO_TIMERState, MAX_CPUS + 1, 3,
	vmstate_timer, CPUTimerState),
	VMSTATE_END_OF_LIST()
	}
	};

	static void slavio_timer_reset(DeviceState *d)
	{
	SLAVIO_TIMERState *s = container_of(d, SLAVIO_TIMERState, busdev.qdev);
	unsigned int i;
	CPUTimerState *curr_timer;

	for (i = 0; i <= MAX_CPUS; i++) {
	curr_timer = &s->cputimer[i];
	curr_timer->limit = 0;
	curr_timer->count = 0;
	curr_timer->reached = 0;
	if (i < s->num_cpus) {
	ptimer_set_limit(curr_timer->timer,
	LIMIT_TO_PERIODS(TIMER_MAX_COUNT32), 1);
	ptimer_run(curr_timer->timer, 0);
	}
	curr_timer->running = 1;
	}
	s->cputimer_mode = 0;
	}

	static int slavio_timer_init1(SysBusDevice *dev)
	{
	int io;
	SLAVIO_TIMERState *s = FROM_SYSBUS(SLAVIO_TIMERState, dev);
	QEMUBH *bh;
	unsigned int i;
	TimerContext *tc;

	for (i = 0; i <= MAX_CPUS; i++) {
	tc = qemu_mallocz(sizeof(TimerContext));
	tc->s = s;
	tc->timer_index = i;

	bh = qemu_bh_new(slavio_timer_irq, tc);
	s->cputimer[i].timer = ptimer_init(bh);
	ptimer_set_period(s->cputimer[i].timer, TIMER_PERIOD);

	io = cpu_register_io_memory(slavio_timer_mem_read,
	slavio_timer_mem_write, tc);
	if (i == 0) {
	sysbus_init_mmio(dev, SYS_TIMER_SIZE, io);
	} else {
	sysbus_init_mmio(dev, CPU_TIMER_SIZE, io);
	}

	sysbus_init_irq(dev, &s->cputimer[i].irq);
	}

	return 0;
	}

	static SysBusDeviceInfo slavio_timer_info = {
	.init = slavio_timer_init1,
	.qdev.name = "slavio_timer",
	.qdev.size = sizeof(SLAVIO_TIMERState),
	.qdev.vmsd = &vmstate_slavio_timer,
	.qdev.reset = slavio_timer_reset,
	.qdev.props = (Property[]) {
	DEFINE_PROP_UINT32("num_cpus", SLAVIO_TIMERState, num_cpus, 0),
	DEFINE_PROP_END_OF_LIST(),
	}
	};

	static void slavio_timer_register_devices(void)
	{
	sysbus_register_withprop(&slavio_timer_info);
	}

	device_init(slavio_timer_register_devices)