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add valid bit to MTTL3 entry #96

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Oct 15, 2024
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add valid bit to MTTL3 entry #96

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8447ac2
add valid bit to MTTL3 entry
rsahita Oct 14, 2024
a9bb6f1
update bit position of valid bit in MTTL3
rsahita Oct 15, 2024
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13 changes: 10 additions & 3 deletions chapter4.adoc
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Original file line number Diff line number Diff line change
Expand Up @@ -59,10 +59,17 @@ The following MTT L3 entry accomodates a 56 bit PAW:
....
{reg: [
{bits: 44, name: 'MTTL2 PPN'},
{bits: 20, name: 'ZERO'},
{bits: 1, name: 'VALID'},
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{bits: 19, name: 'ZERO'},
], config:{lanes: 1, hspace:1024}}
....

The `VALID` bit determines the validity of the `MTTL3` entry. If this bit is
set, the `MTTL3` entry is valid and the `MTTL2 PPN` holds the next level of the
MTT, and the `ZERO` field must be 0. If the `VALID` bit is clear, the entry is
invalid, and all other bits in the entry are don't-cares and may be used freely
by software.

The following are the `MTTL2` entry by XLEN:

[caption="Figure {counter:image}: ", reftext="Figure {image}"]
Expand Down Expand Up @@ -243,8 +250,8 @@ corresponding to the original access type.
an access-fault exception corresponding to the original access type.

4. If any bits or encodings that are reserved for future standard use are
set within _mpte_, stop and raise an access-fault exception corresponding to
the original access type.
set within _mpte_, or _mpte_ is a not-valid `MTTL3` entry, stop and raise an
access-fault exception corresponding to the original access type.

5. Otherwise, the _mpte_ is valid. If (_i_=1) or (_i_=2 and _mpte.type_ is not
`MTT_L1_DIR`), go to step 6. Otherwise, the _mpte_ is a pointer to the next
Expand Down
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