How do I identify Brown out reset (BOR) condition from embedded software?

[CDesh]

I would like to distinguish POR/PDR and BOR condition. Let me know if there is a way to identify this from embedded software for stm32l072cz.

[KnarfB]

Evaluate the __HAL_RCC_GET_FLAG(RCC_FLAG_BORRST) flag and related reset causes at the very beginning of main. Use __HAL_RCC_CLEAR_RESET_FLAGS() to clear the flags after evaluation.

hth

KnarfB

[CDesh]

Thanks for your quick response.

I do not see RCC_FLAG_BORRST flag availability in stm32l0cz MCU. Is there a way to include this flag to my MCU which is available in stm32l4xx.

[KnarfB]

Ooh, you're right. That's different from other families. No idea, sorry. Maybe it cannot be distinguished from a POR?

[Amel NASRI · Accepted solution]

Hi @CDesh​ & @KnarfB​ ,

Comparing both reference manuals of both STM32L4 and STM32L0 and precisely RCC_CSR register, I noted that bit 27 is described as following:

• STM32L4
  • Bit 27 BORRSTF: BOR flag. Set by hardware when a BOR occurs. Cleared by writing to the RMVF bit.
    • 0: No BOR occurred
    • 1: BOR occurred
• STM32L0
  • Bit 27 PORRSTF: POR/PDR reset flag. This bit is set by hardware when a POR/PDR reset occurs. It is cleared by writing to the RMVF bit.
    • 0: No POR/PDR reset occurred
    • 1: POR/PDR reset occurred

So either for L4 or L0, the flag is the same and it is set when a power reset occurs.

In STM32L0, BOR is not available on all devices.

So for both STM32L0 & STM32L4, we can identify POR/PDR/BOR condition based on the bit 27 of RCC_CSR register.

Hope my answer helped you, when your question is answered, please close this topic by choosing Select as Best. This will help other users find that answer faster.

-Amel

[CDesh]

@Amel NASRI​  Thanks for your response.

Is it by part number of STM32L0, where I can identify if BOR is available or not?

If BOR is available, once again how do identify it be different from POR/PDR?

is BOR enabled by default on STM32L0 (where BOR is available)?

[Amel NASRI]

Hi @CDesh​ ,

BOR is not available for devices operating from 1.65 to 3.6 V and the power supply is monitored by the POR/PDR in this case.

For devices operating from 1.8 to 3.6 V, the BOR is always active and unless disabled by option byte it will mask the POR/PDR threshold.

This means that the POR and PDR are used only when the BOR is disabled.

All these details are available in the reference manual RM0367. Have a look to the section 6.2 Power supply supervisor for some more details.

-Amel