Writing to Backup SRAM on STM32H7S78-DK

[mbrossett]

I am trying to use the backup SRAM but get a hard fault when writing to the memory. I have unlocked the backup domain, enabled the backup regulator, and enabled the clock. What other step am I missing?

// unlock backup domain
HAL_PWR_EnableBkUpAccess(); 

// enable the backup SRAM
if (HAL_OK != HAL_PWREx_EnableBkUpReg())
{
	Error_Handler();
}
__HAL_RCC_BKPRAM_CLK_ENABLE();	

// lock the backup domain
HAL_PWR_DisableBkUpAccess();

// Test read and write to backup SRAM
uint32_t magicNumber = 0xAA55;
uint32_t *pBackupSram = (uint32_t *)(0x38800000);
*pBackupSram = magicNumber;
if (magicNumber != *pBackupSram)
{
	Error_Handler();
}
*pBackupSram = 0;
if (0 != *pBackupSram)
{
	Error_Handler();
}

[mbrossett]

I did also verify the BKPRAMEN bit is being set. And the MPU and cache are both disabled. 

[Pavel A. · Accepted solution]

But you disable the backup access in line 12, before write in line 17 ??

[mbrossett]

My understanding is that only enables and disables access to the control registers in the backup domain.  

/**
  * @brief  Enable access to the backup domain (RCC Backup domain control
  *         register RCC_BDCR, RTC registers, TAMP registers, backup registers
  *         and backup SRAM).
  * @note   After a system reset, the backup domain is protected against
  *         possible unwanted write accesses.
  * @retval None.
  */
void HAL_PWR_EnableBkUpAccess(void)
{
  SET_BIT(PWR->CR1, PWR_CR1_DBP);
}

[Pavel A.]

> that only enables and disables access to the control registers

Nope

[mbrossett]

Thanks I’ll try that on Monday. 

[mbrossett]

Yep that did it. Thank you for reviewing the code and quickly finding my mistake!