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sys_clock: Make sys_clock_hw_cycles_per_tick() a proper API

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This was another "global variable" API.  Give it function syntax too.
Also add a warning, because on nRF devices (at least) the cycle clock
runs in kHz and is too slow to give a precise answer here.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
This commit is contained in:
Andy Ross 2018-09-19 11:33:07 -07:00 • committed by Anas Nashif
commit b2e4283555
15 changed files with 59 additions and 66 deletions
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30
include/sys_clock.h
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@ -42,6 +42,20 @@ static inline int sys_clock_hw_cycles_per_sec(void)
#endif
}
/* Note that some systems with comparatively slow cycle counters
* experience precision loss when doing math like this. In the
* general case it is not correct that "cycles" are much faster than
* "ticks".
*/
static inline int sys_clock_hw_cycles_per_tick(void)
{
#ifdef CONFIG_SYS_CLOCK_EXISTS
return sys_clock_hw_cycles_per_sec() / CONFIG_SYS_CLOCK_TICKS_PER_SEC;
#else
return 1; /* Just to avoid a division by zero */
#endif
}
#if defined(CONFIG_SYS_CLOCK_EXISTS) && \
(CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC == 0)
#error "SYS_CLOCK_HW_CYCLES_PER_SEC must be non-zero!"
@ -138,22 +152,6 @@ static inline s64_t __ticks_to_ms(s64_t ticks)
#define _TICK_ALIGN 1
#endif
/*
* sys_clock_us_per_tick global variable represents a number
* of microseconds in one OS timer tick
*
* Note: This variable is deprecated and will be removed soon!
*/
__deprecated extern int sys_clock_us_per_tick;
/*
* sys_clock_hw_cycles_per_tick global variable represents a number
* of platform clock ticks in one OS timer tick.
* sys_clock_hw_cycles_per_tick often represents a value of divider
* of the board clock frequency
*/
extern int sys_clock_hw_cycles_per_tick;
/* SYS_CLOCK_HW_CYCLES_TO_NS64 converts CPU clock cycles to nanoseconds */
#define SYS_CLOCK_HW_CYCLES_TO_NS64(X) \
(((u64_t)(X) * NSEC_PER_SEC) / sys_clock_hw_cycles_per_sec())