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Start alarm by subSeconds: Avoid overflow during conversion from ms to ticks. #113

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Merged
merged 1 commit into from
Nov 27, 2024
Merged

Start alarm by subSeconds: Avoid overflow during conversion from ms to ticks. #113

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11 changes: 4 additions & 7 deletions src/rtc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -947,14 +947,11 @@ void RTC_StartAlarm64(alarm_t name, uint8_t day, uint8_t hours, uint8_t minutes,
if ((initMode == MODE_BINARY_ONLY) || (initMode == MODE_BINARY_MIX)) {
/* We have an SubSecond alarm to set in RTC_BINARY_MIX or RTC_BINARY_ONLY mode */
/* The subsecond in ms is converted in ticks unit 1 tick is 1000 / fqce_apre
* It keeps the subsecond accuracy on 64 bits if needed
* For the conversion, we keep the accuracy on 64 bits, since otherwise we might
* have an overflow even though the conversion result still fits in 32 bits.
*/
if (subSeconds > (uint64_t)UINT32_MAX) {
uint64_t tmp = (subSeconds * (uint64_t)(predivSync + 1)) / (uint64_t)1000;
RTC_AlarmStructure.AlarmTime.SubSeconds = (uint32_t)UINT32_MAX - (uint32_t)tmp;
} else {
RTC_AlarmStructure.AlarmTime.SubSeconds = (uint32_t)((uint32_t)UINT32_MAX - (uint32_t)(subSeconds * (predivSync + 1)) / 1000);
}
uint64_t tmp = (subSeconds * (uint64_t)(predivSync + 1)) / (uint64_t)1000;
RTC_AlarmStructure.AlarmTime.SubSeconds = (uint32_t)UINT32_MAX - (uint32_t)tmp;
} else
#endif /* RTC_ICSR_BIN */
{
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