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29 September 1997 – Subject To Change
Internal Processor Registers
5–5
Instruction Fetch/Decode Unit and Branch Unit (IDU) IPRs
5.1 Instruction Fetch/Decode Unit and Branch Unit (IDU) IPRs
The IDU internal processor registers (IPRs) are described in Section 5.1.1 through
Section 5.1.27.
5.1.1 Istream Translation Buffer Tag (ITB_TAG) Register (101)
ITB_TAG is a write-only register written by hardware on an ITBMISS/IACCVIO,
with the tag field of the faulting virtual address. To ensure the integrity of the
instruction translation buffer (ITB), the TAG and page table entry (PTE) fields of an
ITB entry are updated simultaneously by a write operation to the ITB_PTE register.
This write operation causes the contents of the ITB_TAG register to be written into
the tag field of the ITB location, which is determined by a not-last-used replacement
algorithm. The PTE field is obtained from the HW_MTPR ITB_PTE instruction.
Figure 5–1 shows the ITB_TAG register format.
Figure 5–1 Istream Translation Buffer Tag (ITB_TAG) Register
5.1.2 Instruction Translation Buffer Page Table Entry (ITB_PTE)
Register (102)
ITB_PTE is a read/write register.
Write Format
A write operation to this register writes both the PTE and TAG fields of an ITB loca-
tion determined by a not-last-used replacement algorithm. The TAG and PTE fields
are updated simultaneously to ensure the integrity of the ITB. A write operation to
the ITB_PTE register increments the not-last- used (NLU) pointer, which allows for
writing the entire set of ITB PTE and TAG entries. If the HW_MTPR ITB_PTE
instruction falls in the shadow of a trapping instruction, the NLU pointer may be
incremented multiple times. The TAG field of the ITB location is determined by the
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12
13
31
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32
42
43
63
VA<42:13>
LJ-03473.AI4
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VA<42:13>