uint8_t Values Are Not Changing

[Stnoobs]

I want to download and use firmware (FW) to DDR3. Since DDR is initially disabled, the firmware to activate DDR and the main FW project are separate, and the download procedure is as follows:

1. First, run the DDR activation FW to enable DDR.
2. Download the main FW to DDR and enter debug mode. (The main FW does not perform MPU initialization during download because the debugger has cleared the monitor reset.)

For reference, the MPU is the STM32MP131FAE7, and the DDR is the K4B4G1646E.

I have successfully enabled DDR and modified the linker script of the main FW to download FW to DDR (base address: 0xC0000000). However, there is an issue. Among various possible problems, the most challenging one to solve right now is that the uint8_t variables are not changing as expected.

Even when assigning values to uint8_t variables like:

uint8_t val1 = 10;
uint8_t val2 = 20;
uint8_t val3 = 30;
uint8_t val4 = 40;

they do not change properly. There are no such issues with uint16_t or uint32_t variables.

Here is a portion of my DDR activation FW code. I wrote it with reference to examples from the STM32MP135C-DK board, and there are almost no differences.

 /*Initialize all configured peripherals */
MX_GPIO_Init();
MX_I2C2_Init();
MX_I2C3_Init();
MX_I2C1_Init();
/* USER CODE BEGIN 2 */

pmicInit();
pmic_InitRegulators();

/* USER CODE BEGIN 2 */
/*##-1- Enable MCE ####################*/
__HAL_RCC_MCE_CLK_ENABLE();

/*##-2- TZC configuration ####################*/
__HAL_RCC_TZC_CLK_ENABLE();

/* Configure TZC to allow DDR Region0 R/W non-secure for all IDs */
TZC->GATE_KEEPER = 0;
TZC->REG_ID_ACCESSO = 0xFFFFFFFF;  // Allow DDR Region0 R/W non-secure for all IDs
TZC->REG_ATTRIBUTESO = 0xC0000001;
TZC->GATE_KEEPER |= 1;  // Enable the access in secure Mode  // filter 0 request close

/*##-3- Enable ETZPC & BACKUP SRAM for security ####################*/
__HAL_RCC_ETZPC_CLK_ENABLE();
__HAL_RCC_BKPSRAM_CLK_ENABLE();

/*##-4- Unlock debugger ####################*/
BSEC->BSEC_DENABLE = 0x47f;

/*##-5- Init DDR ####################*/
hddr.wakeup_from_standby = false;
hddr.self_refresh = false;
hddr.zdata = 0;
hddr.clear_bkp = false;

if (HAL_DDR_Init(&hddr) != HAL_OK)
{
    Error_Handler();
}

/*##-6- Check DDR Write/Read ####################*/
*p = DDR_PATTERN;

if (*p != DDR_PATTERN)
{
    Error_Handler();
}

/* Write and read operations */
WRITE_REG(*(volatile uint8_t *)0xC0000004, 0xAA);
WRITE_REG(*(volatile uint8_t *)0xC0000005, 0xBB);
WRITE_REG(*(volatile uint8_t *)0xC0000006, 0xCC);
WRITE_REG(*(volatile uint8_t *)0xC0000007, 0xDD);

uint8_t ret1 = READ_REG(*(volatile uint8_t *)0xC0000004);
uint8_t ret2 = READ_REG(*(volatile uint8_t *)0xC0000005);
uint8_t ret3 = READ_REG(*(volatile uint8_t *)0xC0000006);
uint8_t ret4 = READ_REG(*(volatile uint8_t *)0xC0000007);

The code below works correctly in the DDR activation FW, but in the main FW running on DDR, it is not able to read the values correctly:

WRITE_REG(*(volatile uint8_t *)0xC0000004, 0xAA);
WRITE_REG(*(volatile uint8_t *)0xC0000005, 0xBB);
WRITE_REG(*(volatile uint8_t *)0xC0000006, 0xCC);
WRITE_REG(*(volatile uint8_t *)0xC0000007, 0xDD);

uint8_t ret1 = READ_REG(*(volatile uint8_t *)0xC0000004);
uint8_t ret2 = READ_REG(*(volatile uint8_t *)0xC0000005);
uint8_t ret3 = READ_REG(*(volatile uint8_t *)0xC0000006);
uint8_t ret4 = READ_REG(*(volatile uint8_t *)0xC0000007);

I cannot identify the cause of the issue and need assistance.

Thank you for your help