Multiple Projects(or images) on STM32 Board

Question

I'm here to ask some questions about my project.

Now I'm implementing a lite hypervisor.

So I made three discrete projects(monitor.bin, OS1.bin, OS2.bin), and divided memory.

MEMORY
{
  CCMRAM    (xrw)    : ORIGIN = 0x10000000,   LENGTH = 64K
  RAM    (xrw)    : ORIGIN = 0x20000000,   LENGTH = 32K
  FLASH    (rx)    : ORIGIN = 0x8000000,   LENGTH = 128K
  RAM1    (xrw)    : ORIGIN = 0x20008000,   LENGTH = 32K
  FLASH1    (rx)    : ORIGIN = 0x8020000,   LENGTH = 128K
  RAM2    (xrw)    : ORIGIN = 0x20010000,   LENGTH = 32K
  FLASH2    (rx)    : ORIGIN = 0x8040000,   LENGTH = 128K
}
// the part I revised in linker script file for monitor.bin, STM32F407VGTX_RAM.ld, STM32F407VGTX_FLASH.ld

MEMORY
{
  CCMRAM    (xrw)    : ORIGIN = 0x10000000,   LENGTH = 64K
  RAM    (xrw)    : ORIGIN = 0x20008000,   LENGTH = 32K
  FLASH    (rx)    : ORIGIN = 0x8020000,   LENGTH = 128K
}
// the part I revised in linker script file for OS1.bin, STM32F407VGTX_RAM.ld, STM32F407VGTX_FLASH.ld.
// In case of OS2.bin, RAM ORIGIN = 0x20010000, FLASH ORIGIN = 0x08040000

And I revised the vector offset part of each project for Interrupts in each project.

#define USER_VECT_TAB_ADDRESS

#if defined(USER_VECT_TAB_ADDRESS)
/*!< Uncomment the following line if you need to relocate your vector Table
     in Sram else user remap will be done in Flash. */
/*#define VECT_TAB_SRAM*/
#if defined(VECT_TAB_SRAM)
#define VECT_TAB_BASE_ADDRESS   SRAM_BASE       /*!< Vector Table base address field.
                                                     This value must be a multiple of 0x200. */
#define VECT_TAB_OFFSET         0x00000000U     /*!< Vector Table base offset field.
                                                     This value must be a multiple of 0x200. */
#else
#define VECT_TAB_BASE_ADDRESS   FLASH_BASE      /*!< Vector Table base address field.
                                                     This value must be a multiple of 0x200. */
#define VECT_TAB_OFFSET         0x00020000U     /*!< Vector Table base offset field.
                                                     This value must be a multiple of 0x200. */
#endif /* VECT_TAB_SRAM */
#endif /* USER_VECT_TAB_ADDRESS */

// this is for OS1.bin
// In case for OS2.bin, OFFSET WAS 0x00040000U

After revising up to this point, each project was confirmed to work well.

But what I wanted to do was to implement jump from monitor to OS1 & OS2.

So I revised some codes, but it doesn't work when I set program counter to OS1, OS2.

int main (void) {

    clk();

    RCC->CFGR |= 0x04600000;
    while(1) {
        if(os1 == 0){
            if(os1_first == 1){
                os1 = 1;
                os1_first = 0;
                SCB->VTOR = (uint32_t) 0x8020000;
                __set_MSP(0x20010000);
                __set_PSP(0x20010000);
                asm("BX %0" ::"r"(0x8020000));
            }
            else{
                SCB->VTOR = (uint32_t) 0x8020000;
                __set_MSP(0x20010000);
                __set_PSP(0x20010000);
            }
        }
        else{
            if(os2_first == 1){
                os1 = 0;
                os2_first = 0;
                SCB->VTOR = (uint32_t) 0x8040000;
                __set_MSP(0x20018000);
                __set_PSP(0x20018000);
                asm("BX %0" ::"r"(0x8040000));
            }
            else{

            }
        }
    }
}
// main.c for monitor

int main (void) {

    clk();
        //GPIO, Timer Interrupt init part omitted
    while(1) {
        if(jump_monitor == 1){
            jump_monitor = 0;
            __set_MSP(0x20000000);
            __set_PSP(0x20000000);
            asm("BX %0" ::"r"(0x8000000));
        }
    }
}

void TIM2_IRQHandler() {
    TIM2->SR = 0;
    GPIOD->ODR ^= (1<<13);
    if(first == 1){
        first = 0;
    }
    else{
        jump_monitor = 1;
    }
}

main.c for OS1.bin

The flow of code I want is as follows.

monitor -> OS1(for 2 seconds or something) -> monitor -> OS2(for 2 seconds or something) -> monitor....

But every time I tried to change program counter by using asm("BX"), it falls to Hardfault.

I thought the behavior I wanted was similar to that of the bootloader, so I made some references on bootloader.

I thought about the possibilities of problems.

1. problem when loading projects in memory

: In STM32CUBEIDE, I used load images and symbols in Run Configurations - Startup tab, but didn't work.

: So I used STM32CubeProgrammer, and checked option 'skip flash erase before programming' in download tab. And load three binary files(monitor.bin, OS1.bin, OS2.bin), and modified Start Address.

2. problem before setting program counter

: I set up SCB->VTOR, MSP, PSP before setting up program counter value. But is there any other thing to set up before setting program counter?

: I checked bootloader code, and I found that they set VTOR, MSP, PSP value before jumping to application.

: I thought that jumping to start address of application makes the execution work, from startup code to main.c .

The questions got a little longer as I wrote them, so can anyone answer them?

I want to jump from monitor.bin to OS1.bin and OS2.bin

monitor.bin RAM START ADDRESS: 0x20000000 FLASH START ADDRESS: 0x08000000

OS1.bin RAM START ADDRESS : 0x20008000 FLASH START ADDRESS :0x08020000

OS1.bin RAM START ADDRESS : 0x20010000 FLASH START ADDRESS :0x08040000

Answer 1

I solved. But I don't really understand the mechanism.

Instead of using BX(jump to application by inline assembly), I used Function pointer to reach the address, and the jump occurs.

What is the difference between using Function pointer and using Inline Assembly to reach the address?