MPC555
/
MPC556
BURST BUFFER
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
4-7
The compiler will set the left and right stream boundary at either bit 12 or bit 19. This
will be determined by the most efficient placement of compressed instruction code.
The boundary will be placed between bits 11 and 12 if bit 31 is equal to one. The
boundary will be placed between bits 18 and 19 if bit 31 is equal to zero. The original
right and left streams may span an adjacent base addresses before or after each oth-
er. This fact will also determine the placement of the boundary bit field.
Each stream line may include a variable number of compressed symbols, depending
on how well the bytes in the original stream were compressed.
The decompressor has to maintain two bit pointers (left and right) in order to have ac-
cess to the start location of any instruction’s half.
The decompressor maintains tracking of the base address, to start fetching from the
next address in the memory.
Figure 4-6 Examples of Compressed Symbols Layout
n+1
Uncompressed Code
Compressed Code Stream
11
Boundary assumed to be 12 for both lines
(n) and (n+1) are word addresses in the original uncompressed code
11
Xn+1,1
Xn,1
Xn,2
n
8
15
n+1
n
8
15
0
0
0
0
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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