Cortex-M0 Vector table relocation.

[Vmere.1]

To give a context:

I'm working to implement OTA for an existing project which uses stm32f091xx.

And it already contains separate bootloader(0x08000000) and application(0x08001000) with their own vector tables.

Currently, when a reset occurs, the bootloader which is remapped to 0x0 will call the application at 0x08001000.

Question:

Both bootloader and application have their own vector table.

But on the internet, I found that Cortex-M0 doesn't have a vector table offset.

Just to know more about it, I tried to create a hard fault on the application and surprisingly, the hard fault is now in a location which is relative to the application and not the bootloader.

This is map of the bootloader:

HardFault_Handler                        0x080000e3   Thumb Code     2  startup_stm32f0xx.o(.text)

This is map of the application:

HardFault_Handler                        0x08002447   Thumb Code     2  stm32f0xx_startup.o(.text)

Why is this working? I mean when I set a hard fault, it should go to 0x080000e3  but why it is going to 0x08002447? Can someone give me any ideas about what is happening?

[Tesla DeLorean · Accepted solution]

Typically on the CM0 you have to copy the vector table into the base of RAM, and then remap that into the zero address space. Register in SYSCFG ​

[Vmere.1]

; Vector Table Mapped to Address 0 at Reset
                AREA    RESET, DATA, READONLY
                EXPORT  __Vectors
                EXPORT  __Vectors_End
                EXPORT  __Vectors_Size
 
__Vectors       DCD     __initial_sp                   ; Top of Stack
                DCD     Reset_Handler                  ; Reset Handler
                DCD     NMI_Handler                    ; NMI Handler
                DCD     HardFault_Handler              ; Hard Fault Handler
                DCD     0                              ; Reserved
                DCD     0                              ; Reserved
                DCD     0                              ; Reserved

Now I can relate why the start up file above was defined like this.

They mentioned it in Data section I found it like this.

; Vector Table Mapped to Address 0 at Reset
                AREA    RESET, DATA, READONLY
                EXPORT  __Vectors
                EXPORT  __Vectors_End
                EXPORT  __Vectors_Size
 
__Vectors       DCD     __initial_sp                   ; Top of Stack
                DCD     Reset_Handler                  ; Reset Handler
                DCD     NMI_Handler                    ; NMI Handler
                DCD     HardFault_Handler              ; Hard Fault Handler
                DCD     0                              ; Reserved
                DCD     0                              ; Reserved
                DCD     0                              ; Reserved
                DCD     0                              ; Reserved
                DCD     0                              ; Reserved
                DCD     0                              ; Reserved
                DCD     0                              ; Reserved
                DCD     SVC_Handler                    ; SVCall Handler
                DCD     0                              ; Reserved
                DCD     0                              ; Reserved
                DCD     PendSV_Handler                 ; PendSV Handler
                DCD     SysTick_Handler                ; SysTick Handler

Thank you.