MPC885 Instruction Set
MPC885 PowerQUICC Family Reference Manual, Rev. 2
5-20
Freescale Semiconductor
Note that when data address translation is disabled (MSR[DR] = 0), the Data Cache Block Set to Zero
(dcbz) instruction allocates a cache block in the cache and may not verify that the physical address is valid.
If a cache block is created for an invalid physical address, a machine check condition may result when an
attempt is made to write that cache block back to memory. The cache block could be written back as a
result of the execution of an instruction that causes a cache miss and the invalid addressed cache block is
the target for replacement or a Data Cache Block Store (dcbst) instruction.
Table 5-19
lists the cache instructions that are accessible to user-level programs.
5.2.6
PowerPC OEA Instructions
The PowerPC OEA includes the structure of the memory management model, supervisor-level registers,
and the exception model.
5.2.6.1
System Linkage Instructions
This section describes system linkage instructions (see
Table 5-20
). The sc instruction is a user-level
instruction that permits a user program to call on the system to perform a service and causes the processor
to take an exception. The Return from Interrupt (rfi) instruction is a supervisor-level instruction that is
useful for returning from an exception handler.
5.2.6.2
Processor Control Instructions—OEA
Processor control instructions read from and write to the condition register (CR), machine state register
(MSR), and special-purpose registers (SPRs), and to read from the time base register (TBU or TBL).
Table 5-19. User-Level Cache Instructions
Name
Mnemonic
Syntax
MPC885 Notes
Data Cache Block Touch
dcbt
r
A
,r
B
The appropriate cache block is checked for a hit. If it is a miss,
the instruction is treated as a regular miss, except that bus
error does not cause an exception. If no error occurs, the
cache is updated.
Data Cache Block Touch for
Store
dcbtst
r
A
,r
B
Data Cache Block Set to Zero
dcbz
r
A
,r
B
Executes as defined in the VEA.
Data Cache Block Store
dcbst
r
A
,r
B
Executes as defined in the VEA.
Data Cache Block Flush
dcbf
r
A
,r
B
Executes as defined in the VEA.
Instruction Cache Block
Invalidate
icbi
r
A
,r
B
The MMU translates the EA and the associated instruction
cache block is invalidated if hit.
Table 5-20. System Linkage Instructions
Name Mnemonic
Syntax
System Call
sc
—
Return from Interrupt
rfi
—
Summary of Contents for PowerQUICC MPC870
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