STM32L4+: RTC Calib Out (PB2) and RTC Timestamp Input (PC13) at the same time?

[PK.2]

Hello everybody,

i have a problem with the RTC Calib Out (1Hz) on PB2 and TimeStamp Input PC13 (Board: NUCLEO-L4R5ZI).

• PPS (1 Hz clock) should be on PB2 (RTC_Calib_Out) for time synchronization with other chips.
• PC13 should be configured as TimeStamp Input for events (e.g. 1 Hz)

Calib Out on PB2

With the following code works the calib out pin fine.

hrtc.Instance = RTC;
hrtc.Init.HourFormat = RTC_HOURFORMAT_24;
hrtc.Init.AsynchPrediv = 127;
hrtc.Init.SynchPrediv = 255;
hrtc.Init.OutPut = RTC_OUTPUT_DISABLE;
hrtc.Init.OutPutRemap = RTC_OUTPUT_REMAP_POS1;
hrtc.Init.OutPutPolarity = RTC_OUTPUT_POLARITY_HIGH;
hrtc.Init.OutPutType = RTC_OUTPUT_TYPE_OPENDRAIN;
HAL_RTC_Init(&hrtc);
 
HAL_RTCEx_SetCalibrationOutPut(&hrtc, RTC_CALIBOUTPUT_1HZ);

HAL_StatusTypeDef HAL_RTCEx_SetCalibrationOutPut(RTC_HandleTypeDef *hrtc, uint32_t CalibOutput)
{
 __HAL_LOCK(hrtc); 
 hrtc->State = HAL_RTC_STATE_BUSY;
 __HAL_RTC_WRITEPROTECTION_DISABLE(hrtc); 
 
 hrtc->Instance->CR &= (uint32_t)~RTC_CR_COSEL; /* Clear flags before config */
 hrtc->Instance->CR |= (uint32_t)CalibOutput; /* Configure the RTC_CR register */
 
 __HAL_RTC_CALIBRATION_OUTPUT_ENABLE(hrtc); // ((hrtc)->Instance->CR |= ((0x1UL << (23U))))
 
 __HAL_RTC_WRITEPROTECTION_ENABLE(hrtc); 
 hrtc->State = HAL_RTC_STATE_READY; 
 __HAL_UNLOCK(hrtc);
 
 return HAL_OK;
}

TimeStamp Input on PC13

Is only only the TimeStamp function configured, then it works also as expected. Blue is a clock with e.g. 1 Hz and the red signal is a gpio which will be toggled by the TimeStamp callback function. It works also as expected.

hrtc.Instance = RTC;
hrtc.Init.HourFormat = RTC_HOURFORMAT_24;
hrtc.Init.AsynchPrediv = 127;
hrtc.Init.SynchPrediv = 255;
hrtc.Init.OutPut = RTC_OUTPUT_DISABLE;
hrtc.Init.OutPutRemap = RTC_OUTPUT_REMAP_POS1;
hrtc.Init.OutPutPolarity = RTC_OUTPUT_POLARITY_HIGH;
hrtc.Init.OutPutType = RTC_OUTPUT_TYPE_OPENDRAIN;
HAL_RTC_Init(&hrtc);
 
HAL_RTCEx_SetTimeStamp_IT(&hrtc, RTC_TIMESTAMPEDGE_RISING, RTC_TIMESTAMPPIN_DEFAULT); // default PC13

HAL_StatusTypeDef HAL_RTCEx_SetTimeStamp_IT(RTC_HandleTypeDef *hrtc, uint32_t TimeStampEdge, uint32_t RTC_TimeStampPin)
{
 uint32_t tmpreg;
 
 __HAL_LOCK(hrtc);
 hrtc->State = HAL_RTC_STATE_BUSY;
 
 /* Get the RTC_CR register and clear the bits to be configured */
 tmpreg = (uint32_t)(hrtc->Instance->CR & (uint32_t)~(RTC_CR_TSEDGE | RTC_CR_TSE));
 
 tmpreg |= TimeStampEdge;
 
 /* Disable the write protection for RTC registers */
 __HAL_RTC_WRITEPROTECTION_DISABLE(hrtc);
 
 /* Configure the Time Stamp TSEDGE and Enable bits */
 hrtc->Instance->CR = (uint32_t)tmpreg;
 
 __HAL_RTC_TIMESTAMP_ENABLE(hrtc);
 
 /* Enable IT timestamp */
 __HAL_RTC_TIMESTAMP_ENABLE_IT(hrtc, RTC_IT_TS);
 
 /* RTC timestamp Interrupt Configuration: EXTI configuration */
 __HAL_RTC_TAMPER_TIMESTAMP_EXTI_ENABLE_IT();
 __HAL_RTC_TAMPER_TIMESTAMP_EXTI_ENABLE_RISING_EDGE();
 
 __HAL_RTC_WRITEPROTECTION_ENABLE(hrtc);
 hrtc->State = HAL_RTC_STATE_READY;
 __HAL_UNLOCK(hrtc);
 
 return HAL_OK;
}

Both together (doesn't work)

If I try both together, the calib out will work, but I won't get any TimeStamp events anymore. The signal at the TS input has only a voltage of 1.4 volts. Only the COE and COSEL bits are changed by the pin calib out. What happens here?

hrtc.Instance = RTC;
hrtc.Init.HourFormat = RTC_HOURFORMAT_24;
hrtc.Init.AsynchPrediv = 127;
hrtc.Init.SynchPrediv = 255;
hrtc.Init.OutPut = RTC_OUTPUT_DISABLE;
hrtc.Init.OutPutRemap = RTC_OUTPUT_REMAP_POS1;
hrtc.Init.OutPutPolarity = RTC_OUTPUT_POLARITY_HIGH;
hrtc.Init.OutPutType = RTC_OUTPUT_TYPE_OPENDRAIN;
HAL_RTC_Init(&hrtc);
 
HAL_RTCEx_SetTimeStamp_IT(&hrtc, RTC_TIMESTAMPEDGE_RISING, RTC_TIMESTAMPPIN_DEFAULT); // default PC13
 
HAL_RTCEx_SetCalibrationOutPut(&hrtc, RTC_CALIBOUTPUT_1HZ);

Can someone explain what changes to PC13 when the COE bit is set to 1?

[waclawek.jan]

OK so if you read out the RTC registers, what exactly do you see in those bits, in all three cases?

JW

[PK.2]

I guess i see what i expect.

Case 1

Case 2

Case 3

[waclawek.jan]

Indeed looks logical.

Pity you did not show us the registers when the external 1Hz signal is connected to PC13/RTC_TS - according to your description, at least in case 2 that should have effect on the registers.

I wonder, whether in case 3 that does or does not have similar effect on the registers.

[case 3]

> The signal at the TS input has only a voltage of 1.4 volts.

I don't understand. Isn't that your external 1Hz signal? How is it different from case 2?

JW

[PK.2]

The external signal is the same in case 2 and case 3.

The only difference between case 2 and case 3 is that in case 2 only the RTC_TS is configured (see TSE and TSIE bit).

In case 3 RTC_Calib_Out is also active (see COE and COSEL bit).

In case 3 the voltage is 1.4 V instead of 3.3 V. That's the question. This happens when PB2 is active, but why does it change PC13.

[waclawek.jan]

This sounds like PC13 is turned to output, in spite of TSE bit being set.

Sounds much like a hardware bug.

@Imen DAHMEN​  , can this please be checked? Thanks.

Jan

[PK.2]

Thank you, @Community member​ .

Here is the complete code generated from the CubeMx.

[waclawek.jan]

I wouldn't hold my breath and would work out of the premise that the given combination is simply unavailable. Maybe combination of retaining the tamper function and toggling a pin in RTC interrupt might provide something close to what you intended?

JW

[PK.2]

I wanted to use the RTC_TS for time synchronization because a rising edge triggers an interrupt and at the same time the current time is transferred to the TS register.

With the timestamp I would know how many sub-seconds the RTC of the L4 deviates and could correct this with the shift function.

void HAL_RTCEx_TimeStampEventCallback(RTC_HandleTypeDef *hrtc)
{
 HAL_RTCEx_SetSynchroShift(hrtc, RTC_SHIFTADD1S_RESET, 255 - hrtc->Instance->TSSSR + 1);
 
 HAL_RTCEx_DeactivateTimeStamp(hrtc);
 HAL_RTCEx_SetCalibrationOutPut(hrtc, RTC_CALIBOUTPUT_1HZ);
}

Example

 HAL_RTCEx_SetCalibrationOutPut(&hrtc, RTC_CALIBOUTPUT_1HZ);
 HAL_Delay(3500);
 HAL_RTCEx_DeactivateCalibrationOutPut(&hrtc);
 HAL_Delay(3500);
 HAL_RTCEx_SetTimeStamp_IT(&hrtc, RTC_TIMESTAMPEDGE_RISING, RTC_TIMESTAMPPIN_DEFAULT);

The blue signal is the calibration output and the red signal is the 1 Hz clock with the RTC is to be synchronized.

So that I get an RTC_TS interrupt, I always have to switch off the caliboutput. If the COE bit is set, as you said, the RTC_TS may be configured as an output.

[PK.2]

@Community member​ 

I have assigned PB2 with RTC_Caliboutput and PC13 as exti input with rising edge.

PC13 cannot be used. The input signal is always 1.4 V.

[waclawek.jan]

And what's in the RTC registers now?

JW