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]

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.