The NOLOAD section variable initializes with garbage value on hard reset.

[DVasa.1]

Hi ST team,

I want to define a new section in the ld script so I can use that for variables that have to keep their values in case of soft resets.

I have made some changes in the script as follows,

  .noinit (NOLOAD):

  {

  . = ALIGN(4);

    _noinit = .;

    *(.noinit .noinit.*) 

     . = ALIGN(4) ;

    _end_noinit = .;  

  } >RAM

I have also defined a variable of this kind in the following way,

uint32_t tempVar __attribute__ ((section(".noinit"))) = 0;

At every soft reset, the value of this variable is preserved. However, at every hard reset, the variable is initialized with some garbage value.

What am I missing here?

Thank you.

[TDK]

If you write to RAM, it'll stay there until you change it or it loses power. Many sections of RAM are initialized on startup and the NOLOAD is a way of skipping that initialization. You could do what NOLOAD does manually, or put the variable in a place in RAM which isn't touched or known about by the linker. However, if NOLOAD solves your problem, I don't know why you'd avoid using it.

[TDK]

You'll need to use the RCC->CSR flags to get the functionality you want. The default startup scripts can not do this.

[DVasa.1]

We are using STM32l562CEU6. So in our case, there is no POR-related flag. But there is a BORRST flag. And default value of the VDD cut-off for BOR is 1.71V.

I kept a check of the previous reset condition using the RCC_FLAG_SFTRST and RCC_FLAG_BORRST with __HAL_RCC_GET_FLAG(__FLAG__) API. But If I give a pulse on the NRST pin of the MCU or power cycle the MCU, I can not differentiate using the flag check.

[TDK]

Why doesn't using the BOR flag here work? Do you expect drops in voltage below 1.71V normally?

[DVasa.1]

Using the RCC->CSR register flags, we were able to handle the scenario properly. What we were missing here was clearing the reset flags.

Thank you.