At address 0, for all ARM programs, there are eight ARM exception vectors which are equivalent to eight words. These Vectors are: Reset, Undefined Instruction, Software Interrupt, Prefect Abort, Data Abort, Reserved (used as code size if boot code), Normal Interrupt, and Fast Interrupt. For valid code conditions: check if the first data corresponds to either a Branch instruction B (0xE5) or load register instruction LDR (0xEA). The 6th vector contains the size of the image to download which must be at least smaller than the SAM9 MPU internal SRAM size. Once again, this is product dependant and must be checked in the Boot Program section of the product datasheet.