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sys: time_units: Add Kconfig option for algorithm selection

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Add maximum timeout used for conversion to Kconfig. Option is used
to determine which conversion algorithm to use: faster but overflowing
earlier or slower without early overflow.

Signed-off-by: Krzysztof Chruscinski <krzysztof.chruscinski@nordicsemi.no>
This commit is contained in:
Krzysztof Chruscinski 2022-01-12 10:35:38 +01:00 • committed by Anas Nashif
commit 50c7c7b1e4
3 changed files with 37 additions and 0 deletions
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25
include/sys/time_units.h
View file

@ -64,6 +64,21 @@ static TIME_CONSTEXPR inline int sys_clock_hw_cycles_per_sec(void)
#endif
}
/** @internal
* Macro determines if fast conversion algorithm can be used. It checks if
* maximum timeout represented in source frequency domain and multiplied by
* target frequency fits in 64 bits.
*
* @param from_hz Source frequency.
* @param to_hz Target frequency.
*
* @retval true Use faster algorithm.
* @retval false Use algorithm preventing overflow of intermediate value.
*/
#define Z_TMCVT_USE_FAST_ALGO(from_hz, to_hz) \
((ceiling_fraction(CONFIG_SYS_CLOCK_MAX_TIMEOUT_DAYS * 24ULL * 3600ULL * from_hz, \
UINT32_MAX) * to_hz) <= UINT32_MAX)
/* Time converter generator gadget. Selects from one of three
* conversion algorithms: ones that take advantage when the
* frequencies are an integer ratio (in either direction), or a full
@ -131,7 +146,17 @@ static TIME_CONSTEXPR ALWAYS_INLINE uint64_t z_tmcvt(uint64_t t, uint32_t from_h
} else {
if (result32) {
return (uint32_t)((t * to_hz + off) / from_hz);
} else if (const_hz && Z_TMCVT_USE_FAST_ALGO(from_hz, to_hz)) {
/* Faster algorithm but source is first multiplied by target frequency
* and it can overflow even though final result would not overflow.
* Kconfig option shall prevent use of this algorithm when there is a
* risk of overflow.
*/
return ((t * to_hz + off) / from_hz);
} else {
/* Slower algorithm but input is first divided before being multiplied
* which prevents overflow of intermediate value.
*/
return (t / from_hz) * to_hz + ((t % from_hz) * to_hz + off) / from_hz;
}
}

11
kernel/Kconfig
View file

@ -644,6 +644,17 @@ config TIMEOUT_64BIT
availability of absolute timeout values (which require the
extra precision).
config SYS_CLOCK_MAX_TIMEOUT_DAYS
int "Max timeout (in days) used in conversions"
default 365
help
Value is used in the time conversion static inline function to determine
at compile time which algorithm to use. One algorithm is faster, takes
less code but may overflow if multiplication of source and target
frequency exceeds 64 bits. Second algorithm prevents that. Faster
algorithm is selected for conversion if maximum timeout represented in
source frequency domain multiplied by target frequency fits in 64 bits.
config XIP
bool "Execute in place"
help

1
subsys/testsuite/ztest/include/ztest.h
View file

@ -38,6 +38,7 @@
#define CONFIG_MP_NUM_CPUS 1
#define CONFIG_SYS_CLOCK_TICKS_PER_SEC 100
#define CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC 10000000
#define CONFIG_SYS_CLOCK_MAX_TIMEOUT_DAYS 365
#define ARCH_STACK_PTR_ALIGN 8
/* FIXME: Properly integrate with Zephyr's arch specific code */
#define CONFIG_X86 1