Posted on May 17, 2011 at 14:17Like Neil just said, your boot loader is just a standard appplication.
The binaries created contain the vector table, there's no need to care for anything.
If compiled for flash, these vector tables are aligned to the flash start address.
You can use any size of bootloader you want, just make sure your ''real'' application starts anywhere on a flash sector boundary.
When you offset your application, to e.g. 0x08008000 (that's what I did, my bootloader got quite big ;-)), you will have to do multiple things:
- correct the vector table addresses
- jump from bootloader-application to ''real'' application
- tell the processor to use the new vector table.
There is an application note describing this, but I can't find it.
1) vector table offset:
I changed my linker script to use the new base address.
It depends on your toolchain how you do that, as I'm using Winarm, I had to align
stm32_flash.ld, to align the line
FLASH (rx) : ORIGIN = 0x8000000, LENGTH = 256K
to
FLASH (rx) : ORIGIN = 0x8008000, LENGTH = 224K
2) jump to application code:
You bootloader needs to call the application. This is simple:
{ /* Jump to user application */
JumpAddress = *(vu32*) (ApplicationAddress + 4);
Jump_To_Application = (pFunction) JumpAddress;
/* Initialize user application's Stack Pointer */
Jump_To_Application();
}
So, your setting a function's address to the address of your application +4 (the first 32bit-value is the stack pointer, followed by the reset vector), and call that function.
3) align for the new vector table:
NVIC_SetVectorTable(NVIC_VectTab_FLASH, FIRMWAREBASEADDRESS);
That's all that is needed to jump from one application to another one.
You can do whatever you want to the flash sectors that are not used by the currently running code, e.g. erase and reprogram the bootloader from your application and vice versa.
