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DVasa.1
DVasa.1
Associate
July 29, 2021
Solved

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

  • July 29, 2021
  • 14 replies
  • 4765 views

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.

    This topic has been closed for replies.
    Best answer by TDK

    You can look at the RCC->CSR register to determine the source of the reset and handle them differently, if you want.

    14 replies

    Tesla DeLorean
    Tesla DeLorean
    Guru
    July 29, 2021

    >>What am I missing here?

    Ordering, what startup.s is actually doing, and the scope of the beginning/ending symbols in reality.

    Watch also for where stack falls, or other code running, ie loader or system loader.

    Content will be random at power-up.

    Tips, Buy me a coffee, or three.. PayPal Venmo (See Profile) Up vote any posts that you find helpful, it shows what's working..
    TDK
    TDK
    July 29, 2021

    What does a soft reset vs hard reset mean here? RAM won't be preserved on a power cycle.

    "If you feel a post has answered your question, please click ""Accept as Solution""."
    DVasa.1
    DVasa.1Author
    Associate
    July 30, 2021

    Hi Tesla DeLorean,

    "Content will be random at power-up."

    So, the content of that variable will be garbage at power-up, right?

    Is there any way to prevent that from happening? Can we initialize it on power-up or something?

    DVasa.1
    DVasa.1Author
    Associate
    July 30, 2021

    Hi TDK,

    What I mean by hard reset is the power cycle of the MCU. And by soft reset, I mean that giving reset pulse on the MCU using the reset switch.

    TDK
    TDK
    July 30, 2021
    You can write whatever value you want to it. But then it's not really NOLOAD any longer. If you need it to default to a value on powerup, NOLOAD is not what you want.
    "If you feel a post has answered your question, please click ""Accept as Solution""."
    TDK
    TDKBest answer
    July 30, 2021

    You can look at the RCC->CSR register to determine the source of the reset and handle them differently, if you want.

    "If you feel a post has answered your question, please click ""Accept as Solution""."
    DVasa.1
    DVasa.1Author
    Associate
    August 2, 2021

    Is it possible to initialize a variable on the power cycle, but preserve it on soft resets in RAM memory only?

    Is there any other way than NOLOAD?

    And regarding the RCC->CSR register;

    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.

    Am I missing something here?

    Tesla DeLorean
    Tesla DeLorean
    Guru
    August 2, 2021

    >>Is it possible to initialize a variable on the power cycle, but preserve it on soft resets in RAM memory only? Is there any other way than NOLOAD?

    Not via magic. NOLOAD means that the linker/startup code leave it alone..

    You could use a signature and check over the content to determine if you want to keep the data or memset() it to zero.

    What's the end-goal/purpose you're trying to achieve here? Any NV/BKP RAM in this part? Battery backup for RTC/BKP in design?

    Tips, Buy me a coffee, or three.. PayPal Venmo (See Profile) Up vote any posts that you find helpful, it shows what's working..
    DVasa.1
    DVasa.1Author
    Associate
    August 2, 2021

    What we want here is that a variable should be initialized with a specific value at every power cycle. At run time the value of the variable will be updated. But at every soft reset( i.e; pulse on NRST pin of the MCU), it should be preserved.

    TDK
    TDK
    August 2, 2021

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

    "If you feel a post has answered your question, please click ""Accept as Solution""."
    DVasa.1
    DVasa.1Author
    Associate
    August 2, 2021

    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
    TDK
    August 2, 2021

    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.

    "If you feel a post has answered your question, please click ""Accept as Solution""."
    DVasa.1
    DVasa.1Author
    Associate
    August 3, 2021

    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.

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