diff options
Diffstat (limited to 'chip')
| -rw-r--r-- | chip/stm32/clock-stm32f0.c | 18 |
1 files changed, 14 insertions, 4 deletions
diff --git a/chip/stm32/clock-stm32f0.c b/chip/stm32/clock-stm32f0.c index fe1ccd4aa4..2db0244cf9 100644 --- a/chip/stm32/clock-stm32f0.c +++ b/chip/stm32/clock-stm32f0.c @@ -68,23 +68,33 @@ static int dsleep_recovery_margin_us = 1000000; * subsecond resolution. Set asynchronous clock to 1 Hz. */ +#define RTC_PREDIV_A 1 #ifdef CONFIG_STM32_CLOCK_LSE #define RTC_FREQ (32768 / (RTC_PREDIV_A + 1)) /* Hz */ +/* GCD(RTC_FREQ, 1000000) */ +#define RTC_GCD 64 #else /* LSI clock, 40kHz-ish */ #define RTC_FREQ (40000 / (RTC_PREDIV_A + 1)) /* Hz */ +/* GCD(RTC_FREQ, 1000000) */ +#define RTC_GCD 20000 #endif #define RTC_PREDIV_S (RTC_FREQ - 1) -#define RTC_PREDIV_A 1 -#define US_PER_RTC_TICK (1000000 / RTC_FREQ) + +/* + * There are (1000000 / RTC_FREQ) us per RTC tick, take GCD of both terms + * for conversion calculations to fit in 32 bits. + */ +#define US_GCD (1000000 / RTC_GCD) +#define RTC_FREQ_GCD (RTC_FREQ / RTC_GCD) int32_t rtcss_to_us(uint32_t rtcss) { - return ((RTC_PREDIV_S - (rtcss & 0x7fff)) * US_PER_RTC_TICK); + return ((RTC_PREDIV_S - (rtcss & 0x7fff)) * US_GCD) / RTC_FREQ_GCD; } uint32_t us_to_rtcss(int32_t us) { - return (RTC_PREDIV_S - (us / US_PER_RTC_TICK)); + return RTC_PREDIV_S - us * RTC_FREQ_GCD / US_GCD; } void config_hispeed_clock(void) |