
10-22
ColdFire CF4E Core User’s Manual
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MMU Instructions
For TLB miss faults, the instruction restart model completely reexecutes an instruction
on returning from the exception handler. An instruction can touch two instruction pages (a
32- or 48-bit instruction can straddle two pages) or four data pages (a memory-to-memory
word or longword move where misaligned source and destination operands straddle two
pages). Therefore, one instruction may take two ITLB misses and allocate two ITLB pages
before completion. Likewise, one instruction may require four DTLB misses and allocate
four DTLB pages. Because of this, a pool of unlocked TLB entries must be available if
virtual memory is used.
The above examples show the fewest entries needed to guarantee an instruction can
complete execution. For good MMU performance, more unlocked TLB entries should
be available.
Figure 10-11. Version 4 ColdFire MMU Harvard TLB
10.7 MMU Instructions
The MOVE to USP and MOVE from USP instructions have been added for accessing the
USP. Refer to the
PRM
for more information.
KC1
J
Current address space ID (ASID)
Instruction or data K-Bus address and attributes
Compare
IC1 or OC1 translated address
IC1 or OC1 access control
TLB Tag
Entry 31
TLB Tag
Entry 0
TLB Tag
Entry 31
TLB Tag
Entry 0
To K-Bus control for instruction or
DTLB miss logic
Instruction or dataK-Bus hit
select
Compare
F
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n
.