STM32L4R - is there an application note how to retain 64KB SRAM2 memory?

[crackl1ng]

Hi STM32-Community,

I'm currently using an STM32L4R-MCU and was trying to set it up for standby. By using LoRa, I don't want it to keep requesting an OTAA-Command to join the network, I'm trying to use the SRAM2 Retention of my MCU in Standby-Mode. Googling and skimming through the datasheet, I only found at which adress the 64 KB SRAM are located, but how do I actually write to that memory and also read it back again?

I've neither found an application note, nor an example code. I would be really glad, if someone knows more about this topic.

Kind regards

crackl1ng

[TDK]

Set up a segment in your linker script for SRAM2 and assign variables to be placed there, or create a pointer to that memory and store them manually.

Follow this, but use SRAM2 instead of CCMRAM:

https://www.openstm32.org/Using%2BCCM%2BMemory

[crackl1ng]

Thank you for your reply. That looks very promising and I will try it out. Anyway, there is no application note directly from STM32? Those always have been very informative and usually worked flawlessly.

[crackl1ng · Accepted solution]

I think I have understood it now.

For anyone wondering:

There is a .ld.file, in which the linker gets told, where it should save its data. You have to add RAM2 eg if you want to use SRAM2.

MEMORY
{
RAM (xrw)      : ORIGIN = 0x20000000, LENGTH = 640K
FLASH (rx)      : ORIGIN = 0x8000000, LENGTH = 2048K
RAM2 (xrw)      : ORIGIN = 0x10000000, LENGTH = 64K 
}

followed by

   .ram2 (NOLOAD):
  {
    _sram2 = .;
    *(.ram2*)
    . = ALIGN(4);
    _eram2 = .;
  } >RAM2

Followed by this in the SECTIONS part.

Now data can be initialized within SRAM2 like this:

volatile uint32_t Counter __attribute__((section(".ram2")));
volatile uint32_t test123[20] __attribute__((section(".ram2")));

Et voilà:

I saved n³ (for n from 0 to 19) in test123, and counter was reset on purpose.

Thank you very much for your post, it helped me a lot!

Kind regards

[Anthony Plantin]

Hello there,

Did you find a solution to store the context in SRAM ? For not rejoining the context ? 

I'm struggling with the ST example and the NVM management.

Can you share you're solution or some tips? 

Have a good day 
Anthony