How To Judge The Bootloader Program Is Updating Or Jump To Application Program

I used a updata flag which is a four bytes word and is writed at fixd flash address (0x8000 – 4)

The flag’s value is 0xAABBCCDD. When the bootloader program run, first it judge the updata flag, if the updata falg is not equal 0xAABBCCDD, it will jump to application program. Otherwise, it will run to updata program.