
MOTOROLA
7-10
INSTRUCTION TIMING
For More Information On This Product,
Go to: www.freescale.com
RCPU
REFERENCE MANUAL
An attempt to issue a serializing instruction causes the machine to serialize before
the instruction issues. Notice that only the
sync
instruction guarantees serialization
across PowerPC implementations.
7.3.2 Fetch Serialization
Fetch serialization (also referred to as “fetch synchronization”) causes instruction
fetch to be halted until all instructions currently in the processor (i.e., all issued in-
structions as well as the pre-fetched instructions waiting to be issued) have com-
pleted execution.
Fetch of an
isync
instruction causes fetch serialization. This means that no instruc-
tions following
isync
in the instruction stream are pre-fetched until
isync
and all
previous instructions have completed execution. In addition, when the SER (seri-
alize mode) bit in the ICTRL is asserted, or when the processor is in debug mode,
all instructions cause fetch serialization.
7.4 Context Synchronization
The system call (
sc
) and return from interrupt (
rfi
) instructions are context-synchro-
nizing. Execution of one of these instructions ensures the following:
No higher priority exception exists (
sc
).
All previous instructions have completed to a point where they can no longer
cause an exception.
Previous instructions complete execution in the context (privilege and protec-
tion) under which they were issued.
The instructions following the context-synchronizing instruction execute in the
context established by the instruction.
7.5 Implementation of Special-Purpose Registers
Most special-purpose registers supported by the RCPU are physically implement-
ed within the processor. The following SPRs, however, are physically implemented
outside of the processor (i.e., in another module, such as the system interface unit,
of the microcontroller):
Instruction cache control registers (ICCST, ICADR, and IDDAT)
Time base (TB) and decrementer (DEC)
Development port data register (DPDR)
These registers are read or written with the
mtspr
and
mfspr
instructions. The reg-
isters are physically accessed, however, via the internal L-bus or I-bus as appro-
priate.
The following encodings are reserved in the RCPU for SPRs not located within the
processor:
F
Freescale Semiconductor, Inc.
n
.