MAC7200 datasheet(203/976 Pages) FREESCALE

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System Boot Sequence

MAC7200 Microcontroller Family Reference Manual, Rev. 2

Freescale Semiconductor

125

Note that in both Programming and “Normal” modes, the system is required to dynamically re-map a

memory into address $0000 0000. Because of the pre-fetch/fetch pipeline in the ARM7 core, this requires

some “overlap” between the code in the original memory and the newly swapped in memory. The easiest

way to do this is to insert NOP opcodes into both sets of code at the right location. The following example

illustrates this, using the switch between the bootloader code in the Shadow Block, and the application

code in the Instruction Flash. Note that the example uses “pseudo assembly code”, rather than actual

ARM7 code.

At least 3 NOPs should be used in both the “original” and “new” code.

Address

Original Code

(PBL)

in the Shadow Block

New Code

(App. Code)

in the Flash Main Array

$0000 0000

JMP $0000_0000

NOP

$0000 0004

NOP

$0000 0008

NOP

$0000 000C

NOP

App. Code starts here...

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