IBM PowerPC 604 User Manual page 214

EAO-EA31
Segment Registers
0 7 8 31
0 T
EAO-EA3
•
VSID
15 T VSID
0
v
Select
EA14-EA19
.
.
'-----------t~·
63
EA4-EA13
DTlB
I-
RPN
[ MUX
l..,.-.1-----~
.__ _ _ _ _ _ _ .... ..,. EAO-EA19
Figure 5-7. Segment Register and DTLB Organization
Unless the access is the result of an out-of-order access, a hardware table search operation
begins if there is a TLB miss. If the access is out of order, the table search operation is
postponed until the access is required, at which point the access is no longer out of order.
When the matching PTE is found in memory, it is loaded into a particular TLB entry
selected by the least-recently-used (LRU) replacement algorithm, and the translation
process begins again, this time with a TLB hit.
TLB entries are on-chip copies of PTEs in the page tables in memory and are similar in
structure. TLB entries consist of two words; the upper-order word contains the VSID and
API fields of the upper-order word of the PTE and the lower-order word contains the RPN,
the C bit, the WIMG bits and the PP bits (as in the lower-order word of the PTE). To
uniquely identify a TLB entry as the required PTE, the PTE also contains four more bits of
Chapter 5. Memory Management 5-25