Jump from Openbootloader to the Application

[j_filipe]

Greetings! 
So, I used the OpenBootloader project, and then flashed a GPIO_IOToggle firmware in other area of the flash, close to the example in the video Introduction to Open Bootloader, Part 3: Loading an Application.  In that example the CubeProgrammer flashes through the DFU and check "run after programming". When I unplug the board and turn it back on, the OpenBootloader starts (as expected). 
What I want to do is, as soon as I flash the application, when I turn off the board and turn it on again, the application starts to run and not the bootloader, OR, it starts the bootloader, it checks if there's any application installed, and if yes, it jumps to the application immediately. 
Any clue on how to do that?
Thank you! 

[Saket_Om]

Hello @j_filipe 

You can implement a simple check in your bootloader code. Here’s how you can proceed:

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1. Define the Application Start Address

Decide on the flash address where your application will be located (for example, 0x08008000). Make sure your application is built to start from this address by configuring your linker script or project settings accordingly.

---

2. Add Application Check in Bootloader

In your bootloader’s main function, add code to verify if a valid application is present at the specified address. If so, the bootloader can jump to the application’s entry point. Here’s a typical example for STM32 devices:

#define APP_ADDRESS 0x08008000U

typedef void (*pFunction)(void);

void jumpToApplication(void) {
    uint32_t appStack = *(__IO uint32_t*)APP_ADDRESS;
    uint32_t appEntry = *(__IO uint32_t*)(APP_ADDRESS + 4);

    // Check if stack pointer is in RAM (valid application)
    if ((appStack >= RAM_START) && (appStack < RAM_END)) {
        __disable_irq();
        __set_MSP(appStack);
        pFunction appMain = (pFunction)appEntry;
        appMain();
    }
}

int main(void) {
    HAL_Init();
    // Bootloader initialization...

    // Check for valid application and jump if present
    jumpToApplication();

    // If no valid application, stay in bootloader
    while (1) {
        // Bootloader main loop
    }
}

[j_filipe]

I still need to test it... 
What would it be the RAM_START and RAM_END for STM32U585? Why do you do the appEntry = APP_ADDRESS+4 ? 
What is appMain, the main function? 
Thank you! 

[Saket_Om]

Hello @j_filipe 

The line appEntry = *(uint32_t*)(APP_ADDRESS + 4) retrieves the address of the application's reset handler (the entry point), which is always stored at offset +4 from the application start. The appMain variable is a function pointer to this reset handler, so when you call appMain(), you are transferring control to the application.