path: root/include/hw/timer
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authorPeter Maydell <peter.maydell@linaro.org>2019-05-23 14:47:43 +0100
committerPeter Maydell <peter.maydell@linaro.org>2019-05-23 14:47:43 +0100
commit807420f0b0a71cc7cf38abe06321b5777091e47d (patch)
tree9e16c144647ce73aa3197864d8a350dd19537027 /include/hw/timer
parent2f143d3ad1c05e91cf2cdf5de06d59a80a95e6c8 (diff)
arm: Move system_clock_scale to armv7m_systick.h
The system_clock_scale global is used only by the armv7m systick device; move the extern declaration to the armv7m_systick.h header, and expand the comment to explain what it is and that it should ideally be replaced with a different approach. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com> Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com> Message-id: 20190516163857.6430-2-peter.maydell@linaro.org
Diffstat (limited to 'include/hw/timer')
1 files changed, 22 insertions, 0 deletions
diff --git a/include/hw/timer/armv7m_systick.h b/include/hw/timer/armv7m_systick.h
index cca04defd8..25e5ceacc8 100644
--- a/include/hw/timer/armv7m_systick.h
+++ b/include/hw/timer/armv7m_systick.h
@@ -31,4 +31,26 @@ typedef struct SysTickState {
qemu_irq irq;
} SysTickState;
+ * Multiplication factor to convert from system clock ticks to qemu timer
+ * ticks. This should be set (by board code, usually) to a value
+ * equal to NANOSECONDS_PER_SECOND / frq, where frq is the clock frequency
+ * in Hz of the CPU.
+ *
+ * This value is used by the systick device when it is running in
+ * its "use the CPU clock" mode (ie when SYST_CSR.CLKSOURCE == 1) to
+ * set how fast the timer should tick.
+ *
+ * TODO: we should refactor this so that rather than using a global
+ * we use a device property or something similar. This is complicated
+ * because (a) the property would need to be plumbed through from the
+ * board code down through various layers to the systick device
+ * and (b) the property needs to be modifiable after realize, because
+ * the stellaris board uses this to implement the behaviour where the
+ * guest can reprogram the PLL registers to downclock the CPU, and the
+ * systick device needs to react accordingly. Possibly this should
+ * be deferred until we have a good API for modelling clock trees.
+ */
+extern int system_clock_scale;