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-rw-r--r--hw/timer/armv7m_systick.c112
1 files changed, 84 insertions, 28 deletions
diff --git a/hw/timer/armv7m_systick.c b/hw/timer/armv7m_systick.c
index e43f74114e..21f6d0fd24 100644
--- a/hw/timer/armv7m_systick.c
+++ b/hw/timer/armv7m_systick.c
@@ -18,25 +18,30 @@
#include "qemu/timer.h"
#include "qemu/log.h"
#include "qemu/module.h"
+#include "qapi/error.h"
#include "trace.h"
-/* qemu timers run at 1GHz. We want something closer to 1MHz. */
-#define SYSTICK_SCALE 1000ULL
-
#define SYSTICK_ENABLE (1 << 0)
#define SYSTICK_TICKINT (1 << 1)
#define SYSTICK_CLKSOURCE (1 << 2)
#define SYSTICK_COUNTFLAG (1 << 16)
+#define SYSCALIB_NOREF (1U << 31)
+#define SYSCALIB_SKEW (1U << 30)
+#define SYSCALIB_TENMS ((1U << 24) - 1)
+
int system_clock_scale;
-/* Conversion factor from qemu timer to SysTick frequencies. */
-static inline int64_t systick_scale(SysTickState *s)
+static void systick_set_period_from_clock(SysTickState *s)
{
+ /*
+ * Set the ptimer period from whichever clock is selected.
+ * Must be called from within a ptimer transaction block.
+ */
if (s->control & SYSTICK_CLKSOURCE) {
- return system_clock_scale;
+ ptimer_set_period_from_clock(s->ptimer, s->cpuclk, 1);
} else {
- return 1000;
+ ptimer_set_period_from_clock(s->ptimer, s->refclk, 1);
}
}
@@ -83,7 +88,28 @@ static MemTxResult systick_read(void *opaque, hwaddr addr, uint64_t *data,
val = ptimer_get_count(s->ptimer);
break;
case 0xc: /* SysTick Calibration Value. */
- val = 10000;
+ /*
+ * In real hardware it is possible to make this register report
+ * a different value from what the reference clock is actually
+ * running at. We don't model that (which usually happens due
+ * to integration errors in the real hardware) and instead always
+ * report the theoretical correct value as described in the
+ * knowledgebase article at
+ * https://developer.arm.com/documentation/ka001325/latest
+ * If necessary, we could implement an extra QOM property on this
+ * device to force the STCALIB value to something different from
+ * the "correct" value.
+ */
+ if (!clock_has_source(s->refclk)) {
+ val = SYSCALIB_NOREF;
+ break;
+ }
+ val = clock_ns_to_ticks(s->refclk, 10 * SCALE_MS) - 1;
+ val &= SYSCALIB_TENMS;
+ if (clock_ticks_to_ns(s->refclk, val + 1) != 10 * SCALE_MS) {
+ /* report that tick count does not yield exactly 10ms */
+ val |= SYSCALIB_SKEW;
+ }
break;
default:
val = 0;
@@ -115,6 +141,11 @@ static MemTxResult systick_write(void *opaque, hwaddr addr,
{
uint32_t oldval;
+ if (!clock_has_source(s->refclk)) {
+ /* This bit is always 1 if there is no external refclk */
+ value |= SYSTICK_CLKSOURCE;
+ }
+
ptimer_transaction_begin(s->ptimer);
oldval = s->control;
s->control &= 0xfffffff8;
@@ -122,19 +153,14 @@ static MemTxResult systick_write(void *opaque, hwaddr addr,
if ((oldval ^ value) & SYSTICK_ENABLE) {
if (value & SYSTICK_ENABLE) {
- /*
- * Always reload the period in case board code has
- * changed system_clock_scale. If we ever replace that
- * global with a more sensible API then we might be able
- * to set the period only when it actually changes.
- */
- ptimer_set_period(s->ptimer, systick_scale(s));
ptimer_run(s->ptimer, 0);
} else {
ptimer_stop(s->ptimer);
}
- } else if ((oldval ^ value) & SYSTICK_CLKSOURCE) {
- ptimer_set_period(s->ptimer, systick_scale(s));
+ }
+
+ if ((oldval ^ value) & SYSTICK_CLKSOURCE) {
+ systick_set_period_from_clock(s);
}
ptimer_transaction_commit(s->ptimer);
break;
@@ -177,20 +203,42 @@ static void systick_reset(DeviceState *dev)
{
SysTickState *s = SYSTICK(dev);
- /*
- * Forgetting to set system_clock_scale is always a board code
- * bug. We can't check this earlier because for some boards
- * (like stellaris) it is not yet configured at the point where
- * the systick device is realized.
- */
- assert(system_clock_scale != 0);
-
ptimer_transaction_begin(s->ptimer);
s->control = 0;
+ if (!clock_has_source(s->refclk)) {
+ /* This bit is always 1 if there is no external refclk */
+ s->control |= SYSTICK_CLKSOURCE;
+ }
ptimer_stop(s->ptimer);
ptimer_set_count(s->ptimer, 0);
ptimer_set_limit(s->ptimer, 0, 0);
- ptimer_set_period(s->ptimer, systick_scale(s));
+ systick_set_period_from_clock(s);
+ ptimer_transaction_commit(s->ptimer);
+}
+
+static void systick_cpuclk_update(void *opaque, ClockEvent event)
+{
+ SysTickState *s = SYSTICK(opaque);
+
+ if (!(s->control & SYSTICK_CLKSOURCE)) {
+ /* currently using refclk, we can ignore cpuclk changes */
+ }
+
+ ptimer_transaction_begin(s->ptimer);
+ ptimer_set_period_from_clock(s->ptimer, s->cpuclk, 1);
+ ptimer_transaction_commit(s->ptimer);
+}
+
+static void systick_refclk_update(void *opaque, ClockEvent event)
+{
+ SysTickState *s = SYSTICK(opaque);
+
+ if (s->control & SYSTICK_CLKSOURCE) {
+ /* currently using cpuclk, we can ignore refclk changes */
+ }
+
+ ptimer_transaction_begin(s->ptimer);
+ ptimer_set_period_from_clock(s->ptimer, s->refclk, 1);
ptimer_transaction_commit(s->ptimer);
}
@@ -203,8 +251,10 @@ static void systick_instance_init(Object *obj)
sysbus_init_mmio(sbd, &s->iomem);
sysbus_init_irq(sbd, &s->irq);
- s->refclk = qdev_init_clock_in(DEVICE(obj), "refclk", NULL, NULL, 0);
- s->cpuclk = qdev_init_clock_in(DEVICE(obj), "cpuclk", NULL, NULL, 0);
+ s->refclk = qdev_init_clock_in(DEVICE(obj), "refclk",
+ systick_refclk_update, s, ClockUpdate);
+ s->cpuclk = qdev_init_clock_in(DEVICE(obj), "cpuclk",
+ systick_cpuclk_update, s, ClockUpdate);
}
static void systick_realize(DeviceState *dev, Error **errp)
@@ -215,6 +265,12 @@ static void systick_realize(DeviceState *dev, Error **errp)
PTIMER_POLICY_NO_COUNTER_ROUND_DOWN |
PTIMER_POLICY_NO_IMMEDIATE_RELOAD |
PTIMER_POLICY_TRIGGER_ONLY_ON_DECREMENT);
+
+ if (!clock_has_source(s->cpuclk)) {
+ error_setg(errp, "systick: cpuclk must be connected");
+ return;
+ }
+ /* It's OK not to connect the refclk */
}
static const VMStateDescription vmstate_systick = {