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Fix STM RTC read so it's atomic. #3545

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Merged
merged 1 commit into from
Oct 13, 2020
Merged

Fix STM RTC read so it's atomic. #3545

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18 changes: 17 additions & 1 deletion ports/stm/supervisor/port.c
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Original file line number Diff line number Diff line change
Expand Up @@ -190,6 +190,7 @@ safe_mode_t port_init(void) {
_hrtc.Init.OutPut = RTC_OUTPUT_DISABLE;

HAL_RTC_Init(&_hrtc);
HAL_RTCEx_EnableBypassShadow(&_hrtc);
HAL_NVIC_EnableIRQ(RTC_Alarm_IRQn);

// Turn off SysTick
Expand Down Expand Up @@ -328,9 +329,23 @@ volatile uint32_t cached_date = 0;
volatile uint32_t seconds_to_minute = 0;
volatile uint32_t cached_hours_minutes = 0;
uint64_t port_get_raw_ticks(uint8_t* subticks) {
uint32_t subseconds = rtc_clock_frequency - (uint32_t)(RTC->SSR);
// Disable IRQs to ensure we read all of the RTC registers as close in time as possible. Read
// SSR twice to make sure we didn't read across a tick.
__disable_irq();
uint32_t first_ssr = (uint32_t)(RTC->SSR);
uint32_t time = (uint32_t)(RTC->TR & RTC_TR_RESERVED_MASK);
uint32_t date = (uint32_t)(RTC->DR & RTC_DR_RESERVED_MASK);
uint32_t ssr = (uint32_t)(RTC->SSR);
while (ssr != first_ssr) {
first_ssr = ssr;
time = (uint32_t)(RTC->TR & RTC_TR_RESERVED_MASK);
date = (uint32_t)(RTC->DR & RTC_DR_RESERVED_MASK);
ssr = (uint32_t)(RTC->SSR);
}
__enable_irq();

uint32_t subseconds = rtc_clock_frequency - 1 - ssr;

if (date != cached_date) {
uint32_t year = (uint8_t)((date & (RTC_DR_YT | RTC_DR_YU)) >> 16U);
uint8_t month = (uint8_t)((date & (RTC_DR_MT | RTC_DR_MU)) >> 8U);
Expand All @@ -349,6 +364,7 @@ uint64_t port_get_raw_ticks(uint8_t* subticks) {
hours = (uint8_t)RTC_Bcd2ToByte(hours);
minutes = (uint8_t)RTC_Bcd2ToByte(minutes);
seconds_to_minute = 60 * (60 * hours + minutes);
cached_hours_minutes = hours_minutes;
}
uint8_t seconds = (uint8_t)(time & (RTC_TR_ST | RTC_TR_SU));
seconds = (uint8_t)RTC_Bcd2ToByte(seconds);
Expand Down