MPC562/MPC564 Compression Features
MPC561/MPC563 Reference Manual, Rev. 1.2
A-6
Freescale Semiconductor
When a change of flow occurs, the RCPU issues the new address in compression format. The address
extractor unit of the BBC extracts the base address to instruction memory. When the compressed memory
word is brought to the BBC from the memory, the ICDU uses the IP field of the RCPU-issued address to
decompress the instruction. The BBC provides compressed addresses of the decompressed and next
instructions to the RCPU together with the decompressed instruction.
Shortened word pointer fields of direct branches in compressed mode imply some limitations on compilers
that implement the PowerPC ISA architecture. They should generate binaries, with limited direct branch
displacements to make the compression possible.
If a conditional branch target, generated by a compiler, must be farther than the compression mode
limitation of 4 Kbytes, the compiler may generate a sequence of a conditional branch with opposite
condition to skip the following unconditional branch to the original target.
If the unconditional branch range is still not big enough, the compiler can use branch chains or indirect
branches.
A.2.5
Compressed Address Generation—Indirect Branches
The indirect branch destination address is copied without any change from one of the following RCPU
registers:
•
LR
•
CTR
•
SRR0
See the
RCPU User’s Manual
for more details.
These registers should contain (or be loaded by) the 32-bit compressed address of existing compressed
instructions to be used for correct branching.
The
LR register is automatically updated by the correct value of the “next” instruction compressed address
during subroutine calls by using the
‘
L
’
- form of branch instructions (like
bl
or
bcl
).
The SRR0 register is updated by the correct return compressed address when exceptions are taken by the
RCPU, thus the rfi
instruction obtains the correct return address from an exception handler.
A.2.6
Compressed Address Generation—Exceptions
Upon an exception, the RCPU core issues a regular 0xFFF00X00 or 0x00000X00 exception vector as
specified in the PowerPC ISA architecture. The compressed exception routines (or branches to them)
should start (reside) at the same location in memory as noncompressed ones. The BBC ICDU passes the
vectors unchanged to the MCU internal bus and provides corresponding compressed address to the RCPU
together with the first exception handler instruction opcode.
This scheme allows use of the BBC exception relocation feature regardless of the MCU operational mode.
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.
Summary of Contents for MPC561
Page 84: ...MPC561 MPC563 Reference Manual Rev 1 2 lxxxiv Freescale Semiconductor...
Page 144: ...Signal Descriptions MPC561 MPC563 Reference Manual Rev 1 2 2 46 Freescale Semiconductor...
Page 206: ...Central Processing Unit MPC561 MPC563 Reference Manual Rev 1 2 3 62 Freescale Semiconductor...
Page 302: ...Reset MPC561 MPC563 Reference Manual Rev 1 2 7 14 Freescale Semiconductor...
Page 854: ...Time Processor Unit 3 MPC561 MPC563 Reference Manual Rev 1 2 19 24 Freescale Semiconductor...
Page 968: ...Development Support MPC561 MPC563 Reference Manual Rev 1 2 23 54 Freescale Semiconductor...
Page 1144: ...Internal Memory Map MPC561 MPC563 Reference Manual Rev 1 2 B 34 Freescale Semiconductor...
Page 1212: ...TPU3 ROM Functions MPC561 MPC563 Reference Manual Rev 1 2 D 60 Freescale Semiconductor...
Page 1216: ...Memory Access Timing MPC561 MPC563 Reference Manual Rev 1 2 E 4 Freescale Semiconductor...
