BCM4 boot option byte, software modification on STM32H747

[baptor]

Hi, I am curently working on the STM32H747. I need to have the CM7 booting while the CM4 is not. Then after, the CM4 BOOT is triggered by the CM7.

Using STM32 cube programmer, I am able to disable the BCM4 bit of the SYSCFG_UR1 register.

The required sequency is then working.

BUT, I would like to change this BCM4 bit in the CM7 c code. I found HAL functions to do the work, ( HAL_SYSCFG_DisableCM4BOOT(); ) but when I check the BCM4 bit using cube programmer, it is never changed.

I tried to read the value of this bit using READ_BIT(REG, BIT) function, but it always return 0, even if ticked in cube programmer.

I am using IAR 9.10, and I can check register values SYSCFG_UR0 to SYSCFG_UR17, but the only missing register is the UR1, the one I need...

Is there an access limitation to this register? or do I miss something else?

Thank you

Baptor

[baptor]

Ok, moved forward.

The SYSCFG registers are reseted after each reboot, and are reloaded after the HAL_Init() in the CM7 code. I moved read of BCM4 bit after the HAL_init().

 if( (SYSCFG->UR1 & 0x00010001U ) > 0x0U) ( should detect BCM7 and BCM4 bit)

 {

   CLEAR_BIT(SYSCFG->UR1, SYSCFG_UR1_BCM4);

 }

it goes inside the If().

but if I do :

if( (SYSCFG->UR1 & 0x00000001U ) > 0x0U) ( should detect only BCM4 bit)

it dosn't go in the if.

Also, I need to make the modification permanentely, so to modify the register value only, will maybe not be enought if not saved into flash.

need to check that now.

[baptor]

found some explainations and tried this :

HAL_Init(); // reset of all peripherals + initializes the flash interface and the Systick timer

 HAL_FLASH_Unlock();

 HAL_FLASH_OB_Unlock();

 if( READ_BIT(SYSCFG->UR1, SYSCFG_UR1_BCM4 ))

 {

   HAL_SYSCFG_DisableCM4BOOT();

   HAL_FLASH_OB_Launch();

 }

 HAL_FLASH_OB_Lock();

 HAL_FLASH_Lock();

but still not entering in the If(). but it seems to be the right way to do it.