
CHAPTER 4 MEMORY MANAGEMENT SYSTEM
77
0:
Reserved for future use. Write 0 in a write operation. When this field is read, 0 is read.
(6) EntryHi register (10)
The EntryHi register is write-accessible. It is used to access the built-in TLB. The EntryHi register holds
the high-order bits of a TLB entry for TLB read and write operations. If a TLB Mismatch, TLB Invalid, or
TLB Modified exception occurs, the EntryHi register holds the high-order bit of the TLB entry. The
EntryHi register is also set with the virtual page number (VPN2) for a virtual address where an exception
occurred and the ASID. See Chapter 5 for details of the TLB exception.
The ASID is used to read from or write to the ASID field of the TLB entry. It is also checked with the
ASID of the TLB entry as the ASID of the virtual address during address translation.
The EntryHi register is accessed by the TLBP, TLBWR, TLBWI, and TLBR instructions.
Figure 4-16. EntryHi Register
39
40
(a) 32-bit mode
8
3
21
0
31
11 10
8
7
VPN2
0
ASID
(b) 64-bit mode
62
61
8
3
2
22
29
0
63
11 10
8
7
R
Fill
VPN2
0
ASID
VPN2:
ASID:
Virtual page number divided by two (mapping to two pages)
Address space ID. An 8-bit ASID field that lets multiple processes share the TLB; each
process has a distinct mapping of otherwise identical virtual page numbers.
Space type (00
→
user, 01
→
supervisor, 11
→
kernel). Matches bits 63 and 62 of the virtual
address.
Reserved. Ignored on write. When read, returns zero.
Reserved for future use. Write 0 in a write operation. When this field is read, 0 is read.
R:
Fill:
0: