SRAM2 is only partially retained

[crackl1ng]

Hello dear STM32-Community,

I'm using an STM32L4R and wanted to configure my data retention of SRAM2 for standbymode.

I did the following changes to the linker file:

/* Highest address of the user mode stack */
_estack = 0x10004000;    /* end of RAM */
/* Generate a link error if heap and stack don't fit into RAM */
_Min_Heap_Size = 0x800;      /* required amount of heap  */
_Min_Stack_Size = 0x800; /* required amount of stack */
 
/* Specify the memory areas */
MEMORY
{
RAM (xrw)      : ORIGIN = 0x20000000, LENGTH = 640K
FLASH (rx)      : ORIGIN = 0x8000000, LENGTH = 2048K
SRAM2 (rw)      : ORIGIN = 0x10000000, LENGTH = 16K
}
 
[........]
 
  .data : 
  {
    . = ALIGN(8);
    _sdata = .;        /* create a global symbol at data start */
    *(.data)           /* .data sections */
    *(.data*)          /* .data* sections */
 
    . = ALIGN(8);
    _edata = .;        /* define a global symbol at data end */
  } >SRAM2

As seen on the screenshot the data is acutally saved in SRAM2 (0x10000000) but except for counter, which is specifically initalized with

volatile uint32_t Counter __attribute__((section(".sram2")));

everything else is reset after restarting the programm. What am I doing wrong? Or do i have to manually enter every variable to sram2 myself?

Kind regards and thank you in advance

crackl1ng

[TDK · Accepted solution]

> but except for counter, which is specifically initalized with

> volatile uint32_t Counter __attribute__((section(".sram2")));

> everything else is reset after restarting the programm.

How are other SRAM2 variables initialized.

Is SRAM2 marked as NOLOAD?

[crackl1ng]

The others are just initialized like usual:

float temp = 0.0f; and so on. As stated in the linker file, they are saved in 0x1000000.

And what does NOLOAD mean and where do I find that?

Thank you for your reply.

Kind regards

[Tesla DeLorean]

Google?

Similar to NOINIT (don't initialize)

So that code in startup.s doesn't zero or copy in statics you don't want initialized.

[TDK]

If you’re initializing them, it would make sense that they would be reset at startup. You need to mark them as no load and initialize only if needed.