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Checksum Algorithm MOTLoad Firmware
MVME7100 Single Board Computer Installation and Use (6806800E08A)
95
6.7.1 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);
}
6.7.2 Image Flags
The image flags of the header define various bit options that control how the image will be
executed.
z COPY_TO_RAM
If set, this flag indicates that the image is to be copied to RAM at the address specified in
the header before control is passed. If not set, the image will be executed in flash. In both
instances, control will be passed at the image offset specified in the header from the base
of the image.
z IMAGE_MCG
If set, this flag defines the image as being an Alternate MOTLoad, as opposed to USER,
image. This bit should not be set by developers of alternate boot images.
ImageOffset unsigned integer 1 Offset from header start to entry
ImageFlags unsigned integer 1 Refer to Image Flags on page 95
ImageVersion unsigned integer 1 User defined
Reserved unsigned integer 8 Reserved for expansion
Name Type Size Notes
Table 6-2 MOTLoad Image Flags
Name Value Interpretation
COPY_TO_RAM 0x00000001 Copy image to RAM at ImageRamAddress before execution
IMAGE_MCG 0x00000002 Alternate MOTLoad image
IMAGE_POST 0x00000004 POST image
DONT_AUTO_RUN 0x00000008 Image not to be executed