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arm: Move system_clock_scale to armv7m_systick.h

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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
This commit is contained in:
Peter Maydell 2019-05-23 14:47:43 +01:00
parent 2f143d3ad1
commit 807420f0b0
2 changed files with 22 additions and 4 deletions
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4
include/hw/arm/arm.h
View file

@ -167,8 +167,4 @@ void arm_write_secure_board_setup_dummy_smc(ARMCPU *cpu,
const struct arm_boot_info *info,
hwaddr mvbar_addr);
/* Multiplication factor to convert from system clock ticks to qemu timer
ticks. */
extern int system_clock_scale;
#endif /* HW_ARM_H */

22
include/hw/timer/armv7m_systick.h
View file

@ -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;
#endif