Electronic – Is STM32 RTC halted during debug or not

You probably have the target chip address wrong. You are sending 68h. Either that is not the address of the chip or it is not wired right. The two sequences you show are first a write then a read to that address. In both cases, no ACK was received so the sequence was terminated. Check the datasheet for the chip address.

Added:

I just looked in the datasheet, and the address of that chip really is 68h (page 12), so that's not the issue. That leaves something not wired right at the chip. Your scope traces look good in that a correctly wired and working chip should have responded with ACK as far as I can tell.

We faced the same problem while working with RTC on my STM32F030 Controller. Our alarm interrupt triggered once, but it would never trigger again.

The problem was as follows:

1. We needed to put the system in low power mode when not in use
2. To enable the low power mode, we had to call this function RCC_APB1PeriphResetCmd(RCC_APB1Periph_PWR, ENABLE);
3. This function prevents write access to the DBP bit of register PWR_CR and it makes DBP bit = 0. This bit must be set before we can change any values of RTC registers (as mentioned in reference manual)

Reference manual RM0360 for STM32F030 and STM32F070 states that:

After system reset, the RTC registers are protected against parasitic write access by clearing the DBP bit in the PWR_CR register (refer to the power control section). DBP bit must be set in order to enable RTC registers write access. After RTC domain reset, all the RTC registers are write-protected. Writing to the RTC registers is enabled by writing a key into the Write Protection register, RTC_WPR. The following steps are required to unlock the write protection on all the RTC registers except for RTC_TAFCR and RTC_ISR[13:8].

1. Write ‘0xCA’ into the RTC_WPR register.

2. Write ‘0x53’ into the RTC_WPR register. Writing a wrong key reactivates the write protection. The protection mechanism is not affected by system reset.

We solved the problem by making following changes to the IRQ handler of RTC:

void RTC_IRQHandler(void)
{
   /*  Check line 17 has triggered the IT */
   if ((EXTI->PR & 0x20000) != 0)  
   {  
      /* Makes the DBP bit of PWR_CR register write accessible */
      RCC_APB1PeriphResetCmd(RCC_APB1Periph_PWR, DISABLE);

      /* Writes 1 in the DBP bit of PWR_CR register */
      PWR_BackupAccessCmd(ENABLE);



      /* Your code here ... */


      /* RTC registers are made write accessible */
      RTC_WriteProtectionCmd(DISABLE);

      /* Clear the RTC Alarm-A Flag */
      RTC_ClearFlag(RTC_FLAG_ALRAF);


      /* Makes the RTC registers read only */
      RTC_WriteProtectionCmd(ENABLE);

      /* Locks the DBP bit of PWR_CR register again */
      RCC_APB1PeriphResetCmd(RCC_APB1Periph_PWR, ENABLE);

      /* Clear the EXTI Line 17 Pending bit (Connected internally to RTC Alarm) */
      EXTI->PR |= 0x20000;
  }
}