Motorola MPC533 Reference Manual page 1049

orir31,r31,turn_on_compression_bit_mask
# or alternative to go to uncompressed code:
andi.r31,r31,turn_off_compression_bit_mask
mtsprNRI,r0# Disable external interrupts
mtsprSRR1,r31
mtsprSRR0,r30 # destination address load
rfi # branch and modify MSR
When BBCMCR[EN_COMP] (bit 21) is set, modification of
MSR[DCMPEN] (bit 29) by mtmsr instruction is strictly
forbidden. It may cause the machine to hang until reset.
G.3 Operation Modes
G.3.1 Instruction Fetch
The provides two instruction fetch modes: decompression off and decompression on, and
a burst mode.
The operational modes are defined by RCPU MSR[DCMPEN] bit. If the bit is set, the mode
is decompression on. Otherwise, it is in decompression off.
The RESET routine vector is relocated differently in decompression on and in
decompression off modes. This feature may be used by a software code compression tool
to guarantee that a vocabulary table initialization routine is always executed before
application code is running.
G.3.1.1 Decompression Off Mode
Refer to Section 4.2.1.1, "Decompression Off Mode" for an explanation of decompression
off.
G.3.1.2 Decompression On Mode
In this mode, the 's RCPU sends the two-bit aligned change of flow (COF) address to the
BBC. The BIU transfers the word portion of the address to the U-bus. The BBC continues
to pre-fetch the data from the consequent memory addresses regardless of whether the
RCPU requests them in order to supply data to the ICDU.
In the , the data coming from the instruction memory is not provided directly to the RCPU,
but loaded into the ICDU for decompression. Decompressed instruction code together with
MOTOROLA
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
NOTE
Appendix G. MPC534 Compression Features
Operation Modes
G-17