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Memory Management Unit
e200z3 Power Architecture Core Reference Manual, Rev. 2
5-8
Freescale Semiconductor
The structure of TLB1 is shown in
Figure 5-4. e200z3 TLB1 Organization
5.3.1
IPROT Invalidation Protection in TLB1
The IPROT bit in TLB1 is used to protect TLB entries from invalidation. TLB1 entries with IPROT set
are not invalidated by a tlbivax instruction executed by this processor (even when the INV_ALL
command is indicated), or by a flash invalidate initiated by writing to MMUCSR0[TLB1_FI]. The IPROT
bit can be used to protect critical code and data such as interrupt vectors/handlers in order to guarantee that
the instruction fetch of those vectors never takes a TLB miss exception. Entries with IPROT set can only
be invalidated by writing a 0 to the valid bit of the entry (by using the MAS registers and executing the
tlbwe instruction).
Invalidation operations generated by execution of the tlbivax instruction are guaranteed to invalidate the
entry that translates the address specified in the operand of the tlbivax instruction. Additional entries may
also be invalidated by this operation if they are not protected with IPROT. A precise invalidation can be
performed by writing a 0 to the valid bit of a TLB entry.
5.3.2
Replacement Algorithm for TLB1
The replacement algorithm for TLB1 must be implemented completely by system software. Thus, when
an entry in TLB1 is to be replaced, the software can select which entry to replace and write the entry
number to the MAS0[ESEL] field before executing a tlbwe instruction.
Alternately, the software can load the entry number of the next desired victim into MAS0[NV]. The
e200z3 then automatically loads MAS0[ESEL] from MAS0[NV] on a TLB error condition as shown in
0
15
TLB1
Compare
Compare
RPN
Hit
Real Address
(translated bits, depending on page size)
Virtual Address
Содержание e200z3
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