External SDRAM scattered loading issue

[Lyu.1]

Hi,Master：

MCU: stm32h743ii

IDE:keil
Question：
There is a 32M external SDRAM, and the scatter file is as follows:

LR_IROM1 0x08000000 0x00200000  {    ; load region size_region
  ER_IROM1 0x08000000 0x00200000  {  ; load address = execution address
   *.o (RESET, +First)
   *(InRoot$$Sections)
   *(_drv_set_)
   .ANY (+RO)
   .ANY (+XO)
  }
  
  ...
  
  EXT_SDRAM 0xC0000000 0x2000000 {  ; RW data
   *.o(ext_sdram)
  }
}

Suppose there are some variables in the program that are specified to be located in 'ext_sdram' section.

static lv_color_t buff1[1024 * 600]  __attribute__((used, section("ext_sdram")));
static lv_color_t buff2[1024 * 600]  __attribute__((used, section("ext_sdram")));
...

During the scatter file loading, these variables will be initialized. Therefore, the external SDRAM needs to be initialized before the scatter file loading, as shown below:

Reset_Handler    PROC
                 EXPORT  Reset_Handler                    [WEAK]
        IMPORT  SystemInit
        IMPORT  __low_level_init
        IMPORT  __main

                 LDR     R0, =SystemInit
                 BLX     R0
                 LDR     R0, =__low_level_init
                 BLX     R0
                 LDR     R0, =__main
                 BX      R0
                 ENDP
				 
void __low_level_init(void) 
{
    DIS_INT();
    sys_cache_enable();  
    HAL_Init();  
    sys_stm32_clock_init(192, 5, 2, 4);    // init all clock                     
    delay_init(480);
    sdram_init();  
}

Problems:

1. Before the scatter file loading, modifications to global or static variables within __low_level_init may be overwritten after the scatter file loading.
2. Before the scatter file loading, global or static variables that __low_level_init depends on are not initialized, which may cause abnormal code execution.

I think this approach does not elegantly solve the problem. Is there a more reasonable way to solve it? For example, prevent the scatter file from loading the ext_sdram section, thus eliminating the need to initialize the external SDRAM with __low_level_init before the scatter file loading.
Thank you very much!

[mƎALLEm]

Hello,

You need to initialize the SDRAM in system_stm32h7xx.c / SystemInit().

Already implemented natively in the HAL: the SDRAM is initialized if DATA_IN_ExtSDRAM was defined by the user.

The initialization of the SDRAM is done with SystemInit_ExtMemCtl().

[Lyu.1]

Hi, mƎALLEm
Currently, I haven't handled this by adding relevant initialization in the SystemInit() function. Instead, I've added the UNINIT modifier in the scatter file:

EXT_SDRAM 0xC0000000 UNINIT 0x2000000 {  ; RW data
   .ANY (ext_sdram)
}

And I've also added attribute modifiers to the variables:

__attribute__((zero_init, section("ext_sdram")))

I've found that after these operations, the EXT_SDRAM won't  scatter-loading during the __main stage, thus eliminating the need for pre-initializing the external SDRAM in advance.
I discovered this approach through my own trials, but I'm not sure whether it's reasonable or not. I hope to get guidance from experts. Thank you very much. 

[mƎALLEm · Accepted solution]

This is not a question linked to STM32 MCU but to MDK-ARM toolchain (Keil). You need to contact them directly in their forum. But again you need to initialize the SDRAM before the scatter loading phase as I said before.

[Lyu.1]

ok,Thank you for the good guidance