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hjuns
hjuns
Associate II
June 22, 2020
Question

memory value change after click reset chip

  • June 22, 2020
  • 4 replies
  • 3032 views

Hello,

I use CubeIDE 1.3.0, STM32F769II.

When i debug variable value.

I found value having strange value.

It always happen when i click "reset chip".

0693W000001r9I4QAI.jpg

Memory address is 0x20012C0.

when i start debug. It have 0 value.

0693W000001r9IEQAY.jpg

But when i click "reset chip". 0x20012C0 memory value is changed.

How can i fix it.

Please help me.

Thanks.

This topic has been closed for replies.

4 replies

TDK
TDK
Super User
June 22, 2020

Some variables get initialized during boot. This address could be within one of them. Why do you think it's a problem or that it should be 0?

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hjuns
hjunsAuthor
Associate II
June 22, 2020

This address is .data sector, not .bss.

It is initialized global address sector.

So it should be set 0.

waclawek.jan
waclawek.jan
Super User
June 22, 2020

Place a data breakpoint on that address, or single-step from the reset vector.

JW

Tesla DeLorean
Tesla DeLorean
Guru
June 22, 2020

Review .MAP file, check stack settings.

Walk the Reset_Handler code.

Could also be debugger related.

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hjuns
hjunsAuthor
Associate II
June 23, 2020

You are right.

​

I set break point this address.

Reset_Handler change value sometimes.

But i allocate 0x20012C0 address into .data sector (Initialized global variable) not .bss .

finally 0x20012C0 address value should be set to 0.

Because it initialized global variable.

Reset_Handler: 
 ldr sp, =_estack /* set stack pointer */
 
/* Copy the data segment initializers from flash to SRAM */ 
 movs r1, #0
 b LoopCopyDataInit
 
CopyDataInit:
 ldr r3, =_sidata
 ldr r3, [r3, r1]
 str r3, [r0, r1]
 adds r1, r1, #4
 
LoopCopyDataInit:
 ldr r0, =_sdata
 ldr r3, =_edata
 adds r2, r0, r1
 cmp r2, r3
 bcc CopyDataInit
 ldr r2, =_sbss
 b LoopFillZerobss
/* Zero fill the bss segment. */ 
FillZerobss:
 movs r3, #0
 str r3, [r2]
 adds r2, r2, #4
 
LoopFillZerobss:
 ldr r3, = _ebss
 cmp r2, r3
 bcc FillZerobss

Reset_Handler set 0 in CopyDataInit function.

LoopFillzerobss function change 0x20012C0 address value.

How can i do that. :sad_but_relieved_face:

TDK
TDK
Super User
June 23, 2020

Usually you just define variables and let the linker sort out where to put them. That way there is a clear separation between .data and .bss. The default startup script relies on this to be the case.

> But i allocate 0x20012C0 address into .data sector (Initialized global variable) not .bss .

How did you do this? What does your linker file look like?

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hjuns
hjunsAuthor
Associate II
June 23, 2020

​

Thank you for your answer.

0693W000001rFHCQA2.jpg

I define large size variable.

"Para" variable allocated 0x200004b4 ~ 0x20002014.

​

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