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Backup sram. Does the RTC have to also running

Question asked by kelly.brett on Apr 4, 2015
Latest reply on Apr 4, 2015 by kelly.brett
Hi 
I want to save a Flag during a reboot on STM32F429I
At Main()
I have 

 uint32_t bt;     
     HAL_Init();
       /* Configure the system clock to 180 Mhz */
   SystemClock_Config();
    __PWR_CLK_ENABLE();
   HAL_PWR_EnableBkUpAccess();  
   (*(__IO uint32_t *) (BKPSRAM_BASE + 4)) =  0xCAFEFEED;
//read it back     
    bt = (*(__IO uint32_t *) (BKPSRAM_BASE + 4)) ;


But  bt reads back 0x00    
Do I have to also setup RTC in order to use the  Backup Sram
My clock config below

static void SystemClock_Config(void)
{
  RCC_ClkInitTypeDef RCC_ClkInitStruct;
  RCC_OscInitTypeDef RCC_OscInitStruct;


  /* Enable Power Control clock */
  __PWR_CLK_ENABLE();
  
  /* The voltage scaling allows optimizing the power consumption when the device is 
     clocked below the maximum system frequency, to update the voltage scaling value 
     regarding system frequency refer to product datasheet.  */
  __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE1);
  
  /* Enable HSE Oscillator and activate PLL with HSE as source */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
  RCC_OscInitStruct.HSEState = RCC_HSE_ON;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
  RCC_OscInitStruct.PLL.PLLM = 8;
  RCC_OscInitStruct.PLL.PLLN = 360;
  RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2;
  RCC_OscInitStruct.PLL.PLLQ = 7;
  HAL_RCC_OscConfig(&RCC_OscInitStruct);


  /* Activate the Over-Drive mode */
  HAL_PWREx_ActivateOverDrive();
    
  /* Select PLL as system clock source and configure the HCLK, PCLK1 and PCLK2 
     clocks dividers */
  RCC_ClkInitStruct.ClockType = (RCC_CLOCKTYPE_SYSCLK | RCC_CLOCKTYPE_HCLK | RCC_CLOCKTYPE_PCLK1 | RCC_CLOCKTYPE_PCLK2);
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV4;  
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV2;  
  HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_5);
}

Thanks

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