Motorola MVME3100 manual Valid Boot Images, Checksum Algorithm, Name Type Size

Chapter 3 MOTLoad Firmware

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MVME3100>

Valid Boot Images

Valid boot images whether POST, USER, or Alternate MOTLoad, are located on 1MB boundaries within flash. The image may exceed 1MB in size. An image is determined valid through the presence of two "valid image keys" and other sanity checks. A valid boot image begins with a structure as defined in the following table:

Name	Type	Size	Notes
UserDefined	unsigned integer	8	User defined
ImageKey 1	unsigned integer	1	0x414c5420
ImageKey 2	unsigned integer	1	0x424f4f54
ImageChecksum	unsigned integer	1	Image checksum
ImageSize	unsigned integer	1	Must be a multiple of 4
ImageName	unsigned character	20	User defined
ImageRamAddress	unsigned integer	1	RAM address
ImageOffset	unsigned integer	1	Offset from header start to entry
ImageFlags	unsigned integer	1	Refer to MOTLoad Image Flags on page 32
ImageVersion	unsigned integer	1	User defined
Reserved	unsigned integer	8	Reserved for expansion

Checksum Algorithm

The checksum algorithm is a simple unsigned word add of each word (4 byte) location in the image. The image must be a multiple of 4 bytes in length (word-aligned). The content of the checksum location in the header is not part of the checksum calculation. The calculation assumes the location to be zero. The algorithm is implemented using the following code:

Unsigned int checksum(

Unsigned int *startPtr,/* starting address */

Unsigned int endPtr/* ending address */

) {

unsigned int checksum=0; while (startPtr < endPtr) {

checksum += *startPtr; startPtr++;

}

return(checksum);

}

MVME3100 Single-Board Computer Installation and Use (V3100A/IH1) 31