EB632 datasheet(10/112 Pages) FREESCALE

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Functional Differences Between MSC8101 (Mask 2K42A) and MSC8103 (Mask 2K87M), Rev. 2

Freescale Semiconductor

Boot

5.4

Source Program Data Stream Structure

The source program can be organized into several blocks. Each block can be either a data block or an instruction

block, and it can be loaded to a different specified destination. Each block contains the block size, the location

where the block is loaded, source program words, checksum, checksum enable and the location from which the

next block is loaded.

When each block word is loaded, the routine calculates a checksum by XORing the current word bit by bit with the

result of XORing previous words. The value of bit i of the current result is equal to XORing bit i of the current

word with bit i of the previous result. After the entire block is loaded, the calculated checksum is compared to the

loaded checksum. The checksum comparison and calculation can be skipped by clearing checksum enable bit. The

last block is a special block that indicates end of code. It contains the boot execution start address. Figure 1 shows

the stream structure.

5.5

Source Program Block Structure

The data stream source programs must be structured in the format shown in Table 8.

Figure 1. Boot Code Stream Structure

Table 8. Block Structure

Word

Description

Block size + checksum enable bit (see Figure 2 for layout description)

Next block address

Address where the first block of the source program is to be loaded, most significant part

Address where the first block of the source program is to be loaded, least significant part

First word of source program

Last word of source program

n + 1

Checksum—xor for first block

n + 2

Checksum—xor for first block

2nd offset + 1

Block size + checksum enable bit

2nd offset + 2

Next block address

2nd offset + 3

Address where the second block of the source program is to be loaded, most significant part

2nd offset + 4

Address where the second block of the source program is to be loaded, least significant part

2nd offset + 5

First word of source program

2nd offset + n

Last word of source program

2nd offset +n + 1

Checksum—xor for second block

2nd offset + n + 2

Checksum—xor for second block

Block 1

Block 2

Block

Code End Block

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