The armv7m systick timer is a 24-bit decrementing, wrap-on-zero, clear-on-write counter. Our current implementation has various bugs and dubious workarounds in it (for instance see https://bugs.launchpad.net/qemu/+bug/1872237). We have an implementation of a simple decrementing counter and we put a lot of effort into making sure it handles the interesting corner cases (like "spend a cycle at 0 before reloading") -- ptimer. Rewrite the systick timer to use a ptimer rather than a raw QEMU timer. Unfortunately this is a migration compatibility break, which will affect all M-profile boards. Among other bugs, this fixes https://bugs.launchpad.net/qemu/+bug/1872237 : now writes to SYST_CVR when the timer is enabled correctly do nothing; when the timer is enabled via SYST_CSR.ENABLE, the ptimer code will (because of POLICY_NO_IMMEDIATE_RELOAD) arrange that after one timer tick the counter is reloaded from SYST_RVR and then counts down from there, as the architecture requires. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org> Message-id: 20201015151829.14656-3-peter.maydell@linaro.org
59 lines
1.7 KiB
C
59 lines
1.7 KiB
C
/*
|
|
* ARMv7M SysTick timer
|
|
*
|
|
* Copyright (c) 2006-2007 CodeSourcery.
|
|
* Written by Paul Brook
|
|
* Copyright (c) 2017 Linaro Ltd
|
|
* Written by Peter Maydell
|
|
*
|
|
* This code is licensed under the GPL (version 2 or later).
|
|
*/
|
|
|
|
#ifndef HW_TIMER_ARMV7M_SYSTICK_H
|
|
#define HW_TIMER_ARMV7M_SYSTICK_H
|
|
|
|
#include "hw/sysbus.h"
|
|
#include "qom/object.h"
|
|
#include "hw/ptimer.h"
|
|
|
|
#define TYPE_SYSTICK "armv7m_systick"
|
|
|
|
OBJECT_DECLARE_SIMPLE_TYPE(SysTickState, SYSTICK)
|
|
|
|
struct SysTickState {
|
|
/*< private >*/
|
|
SysBusDevice parent_obj;
|
|
/*< public >*/
|
|
|
|
uint32_t control;
|
|
uint32_t reload;
|
|
int64_t tick;
|
|
ptimer_state *ptimer;
|
|
MemoryRegion iomem;
|
|
qemu_irq irq;
|
|
};
|
|
|
|
/*
|
|
* 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
|