Processor Programming (Continued)
3.3.2.4 TLB Test Registers
The TLB Test Control Register (TR6) contains a com-
mand bit, the upper 20 bits of a linear address, a valid bit
and the attribute bits used in the test operation. The con-
tents of TR6 are used to create the 24-bit TLB tag during
both write and read (TLB lookup) test operations. The
command bit defines whether the test operation is a read
or a write.
Two test registers are used in testing the processor’s
Translation Lookaside Buffer (TLB), TR6 and TR7. Table 3-
14 is a register map for the TLB Test Registers with their bit
definitions given in Table 3-15 on page 58. The test regis-
ters are accessed through MOV instructions that can be
executed only at privilege level 0 (real mode is always
privilege level 0).
The TLB Test Data Register (TR7) contains the upper 20
bits of the physical address (TLB data field), three LRU
bits, two replacement (REP) bits, and a control bit (PL).
During TLB write operations, the physical address in TR7
is written into the TLB entry selected by the contents of
TR6. During TLB lookup operations, the TLB data
selected by the contents of TR6 is loaded into TR7. Table
3-15 lists the bit definitions for TR7 and TR6.
The CPU TLB is a 32-entry, four-way set associative
memory. Each TLB entry consists of a 24-bit tag and 20-
bit data. The 24-bit tag represents the high-order 20 bits
of the linear address, a valid bit, and three attribute bits.
The 20-bit data portion represents the upper 20 bits of the
physical address that corresponds to the linear address.
Table 3-14. TLB Test Registers
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
TR7 Register
TLB Test Data Register (R/W)
Physical Address
0
0
TLB LRU
0
0
P
L
REP
0
0
TR6 Register
TLB Test Control Register (R/W)
Linear Address
V
D
D
#
U
U
#
R
R
#
0
0
0
0
C
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