STM: monotonic time even when RTC is changed

Author: dhalbert

ports/stm/peripherals/rtc.c

@@ -47,6 +47,11 @@ volatile uint32_t cached_date = 0;
 volatile uint32_t seconds_to_minute = 0;
 volatile uint32_t cached_hours_minutes = 0;
 
+// The RTC starts at 2000-01-01 when it comes up.
+// If the RTC is set to a later time, the ticks the RTC returns will be offset by the new time.
+// Remember that offset so it can be removed when returning a monotonic tick count.
+static int64_t rtc_ticks_offset;
+
 volatile bool alarmed_already[2];
 
 bool peripherals_wkup_on = false;
@@ -59,6 +64,8 @@ uint32_t stm32_peripherals_get_rtc_freq(void) {
 }
 
 void stm32_peripherals_rtc_init(void) {
+    rtc_ticks_offset = 0;
+
     // RTC oscillator selection is handled in peripherals/<family>/<line>/clocks.c
     __HAL_RCC_RTC_ENABLE();
     hrtc.Instance = RTC;
@@ -74,49 +81,9 @@ void stm32_peripherals_rtc_init(void) {
     HAL_NVIC_EnableIRQ(RTC_Alarm_IRQn);
 }
 
-#if CIRCUITPY_RTC
-void stm32_peripherals_rtc_get_time(timeutils_struct_time_t *tm) {
-    RTC_DateTypeDef date = {0};
-    RTC_TimeTypeDef time = {0};
-
-    int code;
-    if ((code = HAL_RTC_GetTime(&hrtc, &time, RTC_FORMAT_BIN)) == HAL_OK &&
-        (code = HAL_RTC_GetDate(&hrtc, &date, RTC_FORMAT_BIN)) == HAL_OK) {
-        tm->tm_hour = time.Hours;
-        tm->tm_min = time.Minutes;
-        tm->tm_sec = time.Seconds;
-        tm->tm_wday = date.WeekDay - 1;
-        tm->tm_mday = date.Date;
-        tm->tm_mon = date.Month;
-        tm->tm_year = date.Year + 2000;
-        tm->tm_yday = -1;
-    }
-}
-
-void stm32_peripherals_rtc_set_time(timeutils_struct_time_t *tm) {
-    RTC_DateTypeDef date = {0};
-    RTC_TimeTypeDef time = {0};
-
-    time.Hours = tm->tm_hour;
-    time.Minutes = tm->tm_min;
-    time.Seconds = tm->tm_sec;
-    date.WeekDay = tm->tm_wday + 1;
-    date.Date = tm->tm_mday;
-    date.Month = tm->tm_mon;
-    date.Year = tm->tm_year - 2000;
-    time.DayLightSaving = RTC_DAYLIGHTSAVING_NONE;
-    time.StoreOperation = RTC_STOREOPERATION_RESET;
-
-    if (HAL_RTC_SetTime(&hrtc, &time, RTC_FORMAT_BIN) != HAL_OK ||
-        HAL_RTC_SetDate(&hrtc, &date, RTC_FORMAT_BIN) != HAL_OK) {
-        // todo - throw an exception
-    }
-}
-#endif
-
 // This function is called often for timing so we cache the seconds elapsed computation based on the
 // register value. The STM HAL always does shifts and conversion if we use it directly.
-uint64_t stm32_peripherals_rtc_raw_ticks(uint8_t *subticks) {
+STATIC uint64_t stm32_peripherals_rtc_raw_ticks(uint8_t *subticks) {
     // 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();
@@ -164,6 +131,57 @@ uint64_t stm32_peripherals_rtc_raw_ticks(uint8_t *subticks) {
     return raw_ticks;
 }
 
+// This function returns monotonically increasing ticks by adjusting away the RTC tick offset
+// from the last time the date was set.
+uint64_t stm32_peripherals_rtc_monotonic_ticks(uint8_t *subticks) {
+    return stm32_peripherals_rtc_raw_ticks(subticks) - rtc_ticks_offset;
+}
+
+#if CIRCUITPY_RTC
+void stm32_peripherals_rtc_get_time(timeutils_struct_time_t *tm) {
+    RTC_DateTypeDef date = {0};
+    RTC_TimeTypeDef time = {0};
+
+    int code;
+    if ((code = HAL_RTC_GetTime(&hrtc, &time, RTC_FORMAT_BIN)) == HAL_OK &&
+        (code = HAL_RTC_GetDate(&hrtc, &date, RTC_FORMAT_BIN)) == HAL_OK) {
+        tm->tm_hour = time.Hours;
+        tm->tm_min = time.Minutes;
+        tm->tm_sec = time.Seconds;
+        tm->tm_wday = date.WeekDay - 1;
+        tm->tm_mday = date.Date;
+        tm->tm_mon = date.Month;
+        tm->tm_year = date.Year + 2000;
+        tm->tm_yday = -1;
+    }
+}
+
+void stm32_peripherals_rtc_set_time(timeutils_struct_time_t *tm) {
+    RTC_DateTypeDef date = {0};
+    RTC_TimeTypeDef time = {0};
+
+    uint64_t current_monotonic_ticks = stm32_peripherals_rtc_monotonic_ticks(NULL);
+
+    time.Hours = tm->tm_hour;
+    time.Minutes = tm->tm_min;
+    time.Seconds = tm->tm_sec;
+    date.WeekDay = tm->tm_wday + 1;
+    date.Date = tm->tm_mday;
+    date.Month = tm->tm_mon;
+    date.Year = tm->tm_year - 2000;
+    time.DayLightSaving = RTC_DAYLIGHTSAVING_NONE;
+    time.StoreOperation = RTC_STOREOPERATION_RESET;
+
+    if (HAL_RTC_SetTime(&hrtc, &time, RTC_FORMAT_BIN) != HAL_OK ||
+        HAL_RTC_SetDate(&hrtc, &date, RTC_FORMAT_BIN) != HAL_OK) {
+        // todo - throw an exception
+    }
+
+    rtc_ticks_offset = stm32_peripherals_rtc_raw_ticks(NULL) - current_monotonic_ticks;
+    ;
+}
+#endif
+
 void stm32_peripherals_rtc_assign_wkup_callback(void (*callback)(void)) {
     wkup_callback = callback;
 }

ports/stm/peripherals/rtc.h

@@ -36,7 +36,7 @@
 
 uint32_t stm32_peripherals_get_rtc_freq(void);
 void stm32_peripherals_rtc_init(void);
-uint64_t stm32_peripherals_rtc_raw_ticks(uint8_t *subticks);
+uint64_t stm32_peripherals_rtc_monotonic_ticks(uint8_t *subticks);
 
 void stm32_peripherals_rtc_assign_wkup_callback(void (*callback)(void));
 void stm32_peripherals_rtc_set_wakeup_mode_seconds(uint32_t seconds);

ports/stm/supervisor/port.c

@@ -385,7 +385,7 @@ __attribute__((used)) void HardFault_Handler(void) {
 }
 
 uint64_t port_get_raw_ticks(uint8_t *subticks) {
-    return stm32_peripherals_rtc_raw_ticks(subticks);
+    return stm32_peripherals_rtc_monotonic_ticks(subticks);
 }
 
 // Enable 1/1024 second tick.