qemu-e2k/include/hw/timer/armv7m_systick.h
Peter Maydell 32bd322a01 hw/timer/armv7m_systick: Rewrite to use ptimers
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
2020-10-27 11:15:31 +00:00

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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