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drivers: timer : cortex_m_systick MAX_TICKS protection

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when CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC set to 960M
and CONFIG_SYS_CLOCK_TICKS_PER_SEC set to 100
the MAX_TICKS will be zero or even negative value, which is not
expected.
so need add a protection here downgrading the accuracy to
its as high as possible

also add build message to show that tickless has no effect

fixes: #36766

there used to be a workaround, not a fix,
either change the CONFIG_SYS_CLOCK_TICKS_PER_SEC=200
or
CONFIG_PM to set the CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC
to 32678

Signed-off-by: Hake Huang <hake.huang@oss.nxp.com>
This commit is contained in:
Hake Huang 2024-12-30 11:21:42 +00:00 committed by Chris Friedt
parent 53374c6257
commit 8add9219a7
1 changed files with 15 additions and 3 deletions
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18
drivers/timer/cortex_m_systick.c
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@ -17,11 +17,23 @@
#define COUNTER_MAX 0x00ffffff
#define TIMER_STOPPED 0xff000000
#define CYC_PER_TICK (sys_clock_hw_cycles_per_sec() \
/ CONFIG_SYS_CLOCK_TICKS_PER_SEC)
#define MAX_TICKS ((k_ticks_t)(COUNTER_MAX / CYC_PER_TICK) - 1)
#if defined(CONFIG_TIMER_READS_ITS_FREQUENCY_AT_RUNTIME)
extern unsigned int z_clock_hw_cycles_per_sec;
#define CYC_PER_TICK (z_clock_hw_cycles_per_sec/CONFIG_SYS_CLOCK_TICKS_PER_SEC)
#else
#define CYC_PER_TICK (CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC/CONFIG_SYS_CLOCK_TICKS_PER_SEC)
#endif
/* add MAX_TICKS protection */
#define _MAX_TICKS (int)((k_ticks_t)(COUNTER_MAX / CYC_PER_TICK) - 1)
#define MAX_TICKS ((_MAX_TICKS > 0) ? _MAX_TICKS : 1)
#define MAX_CYCLES (MAX_TICKS * CYC_PER_TICK)
#if (COUNTER_MAX / CYC_PER_TICK) == 1
#pragma message("tickless does nothing as CONFIG_SYS_CLOCK_TICKS_PER_SEC too low")
#endif
/* Minimum cycles in the future to try to program. Note that this is
* NOT simply "enough cycles to get the counter read and reprogrammed
* reliably" -- it becomes the minimum value of the LOAD register, and