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* Copyright (c) 2006-2007 CodeSourcery.
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* Written by Paul Brook
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* Copyright (c) 2017 Linaro Ltd
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* Written by Peter Maydell
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* This code is licensed under the GPL (version 2 or later).
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#include "qemu/osdep.h"
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#include "hw/timer/armv7m_systick.h"
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#include "qemu-common.h"
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#include "hw/sysbus.h"
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#include "qemu/timer.h"
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/* qemu timers run at 1GHz. We want something closer to 1MHz. */
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#define SYSTICK_SCALE 1000ULL
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#define SYSTICK_ENABLE (1 << 0)
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#define SYSTICK_TICKINT (1 << 1)
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#define SYSTICK_CLKSOURCE (1 << 2)
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#define SYSTICK_COUNTFLAG (1 << 16)
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int system_clock_scale;
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/* Conversion factor from qemu timer to SysTick frequencies. */
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static inline int64_t systick_scale(SysTickState *s)
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if (s->control & SYSTICK_CLKSOURCE) {
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return system_clock_scale;
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static void systick_reload(SysTickState *s, int reset)
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/* The Cortex-M3 Devices Generic User Guide says that "When the
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* ENABLE bit is set to 1, the counter loads the RELOAD value from the
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* SYST RVR register and then counts down". So, we need to check the
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* ENABLE bit before reloading the value.
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trace_systick_reload();
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if ((s->control & SYSTICK_ENABLE) == 0) {
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s->tick = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
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s->tick += (s->reload + 1) * systick_scale(s);
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timer_mod(s->timer, s->tick);
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static void systick_timer_tick(void *opaque)
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SysTickState *s = (SysTickState *)opaque;
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trace_systick_timer_tick();
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s->control |= SYSTICK_COUNTFLAG;
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if (s->control & SYSTICK_TICKINT) {
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/* Tell the NVIC to pend the SysTick exception */
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qemu_irq_pulse(s->irq);
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s->control &= ~SYSTICK_ENABLE;
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static uint64_t systick_read(void *opaque, hwaddr addr, unsigned size)
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SysTickState *s = opaque;
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case 0x0: /* SysTick Control and Status. */
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s->control &= ~SYSTICK_COUNTFLAG;
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case 0x4: /* SysTick Reload Value. */
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case 0x8: /* SysTick Current Value. */
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if ((s->control & SYSTICK_ENABLE) == 0) {
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t = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
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val = ((s->tick - (t + 1)) / systick_scale(s)) + 1;
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/* The interrupt in triggered when the timer reaches zero.
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However the counter is not reloaded until the next clock
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tick. This is a hack to return zero during the first tick. */
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if (val > s->reload) {
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case 0xc: /* SysTick Calibration Value. */
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qemu_log_mask(LOG_GUEST_ERROR,
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"SysTick: Bad read offset 0x%" HWADDR_PRIx "\n", addr);
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trace_systick_read(addr, val, size);
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static void systick_write(void *opaque, hwaddr addr,
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uint64_t value, unsigned size)
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SysTickState *s = opaque;
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trace_systick_write(addr, value, size);
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case 0x0: /* SysTick Control and Status. */
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uint32_t oldval = s->control;
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s->control &= 0xfffffff8;
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s->control |= value & 7;
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if ((oldval ^ value) & SYSTICK_ENABLE) {
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int64_t now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
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if (value & SYSTICK_ENABLE) {
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timer_mod(s->timer, s->tick);
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systick_reload(s, 1);
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} else if ((oldval ^ value) & SYSTICK_CLKSOURCE) {
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/* This is a hack. Force the timer to be reloaded
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when the reference clock is changed. */
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systick_reload(s, 1);
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case 0x4: /* SysTick Reload Value. */
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case 0x8: /* SysTick Current Value. Writes reload the timer. */
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systick_reload(s, 1);
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s->control &= ~SYSTICK_COUNTFLAG;
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qemu_log_mask(LOG_GUEST_ERROR,
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"SysTick: Bad write offset 0x%" HWADDR_PRIx "\n", addr);
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static const MemoryRegionOps systick_ops = {
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.read = systick_read,
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.write = systick_write,
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.endianness = DEVICE_NATIVE_ENDIAN,
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.valid.min_access_size = 4,
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.valid.max_access_size = 4,
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static void systick_reset(DeviceState *dev)
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SysTickState *s = SYSTICK(dev);
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static void systick_instance_init(Object *obj)
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SysBusDevice *sbd = SYS_BUS_DEVICE(obj);
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SysTickState *s = SYSTICK(obj);
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memory_region_init_io(&s->iomem, obj, &systick_ops, s, "systick", 0xe0);
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sysbus_init_mmio(sbd, &s->iomem);
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sysbus_init_irq(sbd, &s->irq);
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s->timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, systick_timer_tick, s);
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static const VMStateDescription vmstate_systick = {
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.name = "armv7m_systick",
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.minimum_version_id = 1,
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.fields = (VMStateField[]) {
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VMSTATE_UINT32(control, SysTickState),
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VMSTATE_UINT32(reload, SysTickState),
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VMSTATE_INT64(tick, SysTickState),
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VMSTATE_TIMER_PTR(timer, SysTickState),
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VMSTATE_END_OF_LIST()
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static void systick_class_init(ObjectClass *klass, void *data)
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DeviceClass *dc = DEVICE_CLASS(klass);
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dc->vmsd = &vmstate_systick;
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dc->reset = systick_reset;
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static const TypeInfo armv7m_systick_info = {
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.name = TYPE_SYSTICK,
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.parent = TYPE_SYS_BUS_DEVICE,
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.instance_init = systick_instance_init,
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.instance_size = sizeof(SysTickState),
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.class_init = systick_class_init,
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static void armv7m_systick_register_types(void)
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type_register_static(&armv7m_systick_info);
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type_init(armv7m_systick_register_types)