Operation Modes; Instruction Fetch; Decompression Off Mode; Decompression On Mode - Motorola MPC533 Reference Manual

Operation Modes

— Four RAM entries, 38 bits each, which hold up to four valid instruction
OPCODES (32 bits). The six extra bits are used by ICDU in decompression on
mode.
— A 32-bit register that stores the values used to calculate the address following the
last valid instruction.
• FIFO removal policy management is implemented for the eight BTEs
• Software-controlled BTB enable/disable and invalidate
• User transparent – No user management is required
4.2 Operation Modes
4.2.1

Instruction Fetch

The BBC provides two instruction fetch modes: decompression off and decompression on.
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.
4.2.1.1

Decompression Off Mode

In this mode, the MPC534 microcontroller's bus interface unit (BIU) module transfers fetch
accesses from the RCPU to the U-bus. When a new access is issued by the RCPU, it is
transferred in parallel to both the IMPU and the BIU. The IMPU compares the address of
the access to its region programming. The BIU checks if the access can be immediately
transferred to the U-bus, otherwise it requests the U-bus for the next clock.
For the MPC534, the BIU may be programmed for burstable or non-burstable access. If the
BIU is programmed for burstable access, the U-bus address phase transaction is
accompanied by the burst request attribute. If burstable access is allowed by the U-bus
slave, the BIU continues current access as burstable, otherwise current access is executed
as a single access. If any protection violation is detected by the IMPU, the current U-bus
access is aborted by the BIU and an exception is signaled to the RCPU.
Show cycle, program trace and debug port access attributes accompanying the RCPU
access are forwarded by the BIU along with the U-bus access.
4.2.1.2

Decompression On Mode

See Appendix G, "MPC534 Compression Features" for explanation of the decompression
on mode.
4-4
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
MPC533 Reference Manual MOTOROLA