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31
31
(15)
VPN (31–17) VPN (11–10) ASID SH SZ V
Legend:
VPN: Virtual page number. Top 22 bits of virtual address for a 1-kbyte page, or top 20 bits of virtual
address for a 4-kbyte page. Since VPN bits 16-12 are used as the index number, they are
not stored in the TLB entry.
ASID: Address space identifier. Indicates the process that can access a virtual page. In single
virtual memory mode and user mode, or in multiple virtual memory mode, if the SH bit is 0,
the address is compared with the ASID in PTEH when address comparison is performed.
SH: Share status bit
0 = Page not shared between processes
1 = Page shared between processes
SZ: Page-size bit
0 = 1-kbyte page
1 = 4-kbyte page
V: Valid bit. Indicates whether entry is valid.
0 = Invalid
1 = Valid
Cleared to 0 by a power-on reset. Not affected by a manual reset.
PPN: Physical page number. Top 22 bits of physical address. PPN bits 11-10 are not used in case
of a 4-kbyte page. Attention must be paid to the synonym problem in case of a 1-kbyte page
(see section 3.4.4).
PR: Set the most significant bit to 0.
Protection key field. 2-bit field encoded to define the access rights to the page.
00: Reading only is possible in privileged mode.
01: Reading/writing is possible in privileged mode.
10: Reading only is possible in privileged/user mode.
11: Reading/writing is possible in privileged/user mode.
C: Cacheable bit. Indicates whether the page is cacheable.
0: Non-cacheable
1: Cacheable
D: Dirty bit. Indicates whether the page has been written to.
0 = Not written to
1 = Written to
68
VPN
Virtual address (1-kbyte page)
VPN
Virtual address (4-kbyte page)
(2)
(8)
(1)
(1)
TLB entry
Figure 3.6 Virtual Address and TLB Structure
10
9
Offset
12
11
Offset
(1)
(19)
PPN
0
0
(2)
(1) (1)
PR
C D
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