hw/timer/armv7m_systick.c

   1 /*
   2  * ARMv7M SysTick timer
   3  *
   4  * Copyright (c) 2006-2007 CodeSourcery.
   5  * Written by Paul Brook
   6  * Copyright (c) 2017 Linaro Ltd
   7  * Written by Peter Maydell
   8  *
   9  * This code is licensed under the GPL (version 2 or later).
  10  */
  11
  12 #include "qemu/osdep.h"
  13 #include "hw/timer/armv7m_systick.h"
  14 #include "migration/vmstate.h"
  15 #include "hw/irq.h"
  16 #include "hw/sysbus.h"
  17 #include "qemu/timer.h"
  18 #include "qemu/log.h"
  19 #include "qemu/module.h"
  20 #include "trace.h"
  21
  22 /* qemu timers run at 1GHz.   We want something closer to 1MHz.  */
  23 #define SYSTICK_SCALE 1000ULL
  24
  25 #define SYSTICK_ENABLE    (1 << 0)
  26 #define SYSTICK_TICKINT   (1 << 1)
  27 #define SYSTICK_CLKSOURCE (1 << 2)
  28 #define SYSTICK_COUNTFLAG (1 << 16)
  29
  30 int system_clock_scale;
  31
  32 /* Conversion factor from qemu timer to SysTick frequencies.  */
  33 static inline int64_t systick_scale(SysTickState *s)
  34 {
  35     if (s->control & SYSTICK_CLKSOURCE) {
  36         return system_clock_scale;
  37     } else {
  38         return 1000;
  39     }
  40 }
  41
  42 static void systick_reload(SysTickState *s, int reset)
  43 {
  44     /* The Cortex-M3 Devices Generic User Guide says that "When the
  45      * ENABLE bit is set to 1, the counter loads the RELOAD value from the
  46      * SYST RVR register and then counts down". So, we need to check the
  47      * ENABLE bit before reloading the value.
  48      */
  49     trace_systick_reload();
  50
  51     if ((s->control & SYSTICK_ENABLE) == 0) {
  52         return;
  53     }
  54
  55     if (reset) {
  56         s->tick = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
  57     }
  58     s->tick += (s->reload + 1) * systick_scale(s);
  59     timer_mod(s->timer, s->tick);
  60 }
  61
  62 static void systick_timer_tick(void *opaque)
  63 {
  64     SysTickState *s = (SysTickState *)opaque;
  65
  66     trace_systick_timer_tick();
  67
  68     s->control |= SYSTICK_COUNTFLAG;
  69     if (s->control & SYSTICK_TICKINT) {
  70         /* Tell the NVIC to pend the SysTick exception */
  71         qemu_irq_pulse(s->irq);
  72     }
  73     if (s->reload == 0) {
  74         s->control &= ~SYSTICK_ENABLE;
  75     } else {
  76         systick_reload(s, 0);
  77     }
  78 }
  79
  80 static MemTxResult systick_read(void *opaque, hwaddr addr, uint64_t *data,
  81                                 unsigned size, MemTxAttrs attrs)
  82 {
  83     SysTickState *s = opaque;
  84     uint32_t val;
  85
  86     if (attrs.user) {
  87         /* Generate BusFault for unprivileged accesses */
  88         return MEMTX_ERROR;
  89     }
  90
  91     switch (addr) {
  92     case 0x0: /* SysTick Control and Status.  */
  93         val = s->control;
  94         s->control &= ~SYSTICK_COUNTFLAG;
  95         break;
  96     case 0x4: /* SysTick Reload Value.  */
  97         val = s->reload;
  98         break;
  99     case 0x8: /* SysTick Current Value.  */
 100     {
 101         int64_t t;
 102
 103         if ((s->control & SYSTICK_ENABLE) == 0) {
 104             val = 0;
 105             break;
 106         }
 107         t = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 108         if (t >= s->tick) {
 109             val = 0;
 110             break;
 111         }
 112         val = ((s->tick - (t + 1)) / systick_scale(s)) + 1;
 113         /* The interrupt in triggered when the timer reaches zero.
 114            However the counter is not reloaded until the next clock
 115            tick.  This is a hack to return zero during the first tick.  */
 116         if (val > s->reload) {
 117             val = 0;
 118         }
 119         break;
 120     }
 121     case 0xc: /* SysTick Calibration Value.  */
 122         val = 10000;
 123         break;
 124     default:
 125         val = 0;
 126         qemu_log_mask(LOG_GUEST_ERROR,
 127                       "SysTick: Bad read offset 0x%" HWADDR_PRIx "\n", addr);
 128         break;
 129     }
 130
 131     trace_systick_read(addr, val, size);
 132     *data = val;
 133     return MEMTX_OK;
 134 }
 135
 136 static MemTxResult systick_write(void *opaque, hwaddr addr,
 137                                  uint64_t value, unsigned size,
 138                                  MemTxAttrs attrs)
 139 {
 140     SysTickState *s = opaque;
 141
 142     if (attrs.user) {
 143         /* Generate BusFault for unprivileged accesses */
 144         return MEMTX_ERROR;
 145     }
 146
 147     trace_systick_write(addr, value, size);
 148
 149     switch (addr) {
 150     case 0x0: /* SysTick Control and Status.  */
 151     {
 152         uint32_t oldval = s->control;
 153
 154         s->control &= 0xfffffff8;
 155         s->control |= value & 7;
 156         if ((oldval ^ value) & SYSTICK_ENABLE) {
 157             int64_t now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 158             if (value & SYSTICK_ENABLE) {
 159                 if (s->tick) {
 160                     s->tick += now;
 161                     timer_mod(s->timer, s->tick);
 162                 } else {
 163                     systick_reload(s, 1);
 164                 }
 165             } else {
 166                 timer_del(s->timer);
 167                 s->tick -= now;
 168                 if (s->tick < 0) {
 169                     s->tick = 0;
 170                 }
 171             }
 172         } else if ((oldval ^ value) & SYSTICK_CLKSOURCE) {
 173             /* This is a hack. Force the timer to be reloaded
 174                when the reference clock is changed.  */
 175             systick_reload(s, 1);
 176         }
 177         break;
 178     }
 179     case 0x4: /* SysTick Reload Value.  */
 180         s->reload = value;
 181         break;
 182     case 0x8: /* SysTick Current Value.  Writes reload the timer.  */
 183         systick_reload(s, 1);
 184         s->control &= ~SYSTICK_COUNTFLAG;
 185         break;
 186     default:
 187         qemu_log_mask(LOG_GUEST_ERROR,
 188                       "SysTick: Bad write offset 0x%" HWADDR_PRIx "\n", addr);
 189     }
 190     return MEMTX_OK;
 191 }
 192
 193 static const MemoryRegionOps systick_ops = {
 194     .read_with_attrs = systick_read,
 195     .write_with_attrs = systick_write,
 196     .endianness = DEVICE_NATIVE_ENDIAN,
 197     .valid.min_access_size = 4,
 198     .valid.max_access_size = 4,
 199 };
 200
 201 static void systick_reset(DeviceState *dev)
 202 {
 203     SysTickState *s = SYSTICK(dev);
 204
 205     /*
 206      * Forgetting to set system_clock_scale is always a board code
 207      * bug. We can't check this earlier because for some boards
 208      * (like stellaris) it is not yet configured at the point where
 209      * the systick device is realized.
 210      */
 211     assert(system_clock_scale != 0);
 212
 213     s->control = 0;
 214     s->reload = 0;
 215     s->tick = 0;
 216     timer_del(s->timer);
 217 }
 218
 219 static void systick_instance_init(Object *obj)
 220 {
 221     SysBusDevice *sbd = SYS_BUS_DEVICE(obj);
 222     SysTickState *s = SYSTICK(obj);
 223
 224     memory_region_init_io(&s->iomem, obj, &systick_ops, s, "systick", 0xe0);
 225     sysbus_init_mmio(sbd, &s->iomem);
 226     sysbus_init_irq(sbd, &s->irq);
 227 }
 228
 229 static void systick_realize(DeviceState *dev, Error **errp)
 230 {
 231     SysTickState *s = SYSTICK(dev);
 232     s->timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, systick_timer_tick, s);
 233 }
 234
 235 static const VMStateDescription vmstate_systick = {
 236     .name = "armv7m_systick",
 237     .version_id = 1,
 238     .minimum_version_id = 1,
 239     .fields = (VMStateField[]) {
 240         VMSTATE_UINT32(control, SysTickState),
 241         VMSTATE_UINT32(reload, SysTickState),
 242         VMSTATE_INT64(tick, SysTickState),
 243         VMSTATE_TIMER_PTR(timer, SysTickState),
 244         VMSTATE_END_OF_LIST()
 245     }
 246 };
 247
 248 static void systick_class_init(ObjectClass *klass, void *data)
 249 {
 250     DeviceClass *dc = DEVICE_CLASS(klass);
 251
 252     dc->vmsd = &vmstate_systick;
 253     dc->reset = systick_reset;
 254     dc->realize = systick_realize;
 255 }
 256
 257 static const TypeInfo armv7m_systick_info = {
 258     .name = TYPE_SYSTICK,
 259     .parent = TYPE_SYS_BUS_DEVICE,
 260     .instance_init = systick_instance_init,
 261     .instance_size = sizeof(SysTickState),
 262     .class_init = systick_class_init,
 263 };
 264
 265 static void armv7m_systick_register_types(void)
 266 {
 267     type_register_static(&armv7m_systick_info);
 268 }
 269
 270 type_init(armv7m_systick_register_types)