Atc Organization - Motorola M68060 User Manual

Memory Management Unit
4.3 ADDRESS TRANSLATION CACHES
The ATCs in the MMUs are four-way set-associative caches that each store 64 logical-to-
physical address translations and associated page information similar in form to the corre-
sponding page descriptors in memory. The purpose of the ATC is to provide a fast mecha-
nism for address translation by avoiding the overhead associated with a table search of the
logical-to-physical mapping of recently used logical addresses. Figure 4-19 illustrates the
organization of the ATC.
31
F
PAGE FRAME
C
2
16
PAGE SIZE
17
Each ATC entry consists of a physical address, attribute information from a corresponding
page descriptor, and a tag that contains a logical address and status information. Figure 4-
20, which illustrates the entry and tag fields, is followed by field definitions listed in alphabet-
ical order.
4-24
16 12
PAGE OFFSET
12
1 1
MUX
1 3
SET
SET 0
SELECT
SET 1
4
SET 15
17
COMPARATOR
Figure 4-19. ATC Organization
M68060 USER'S MANUAL
0
TAG ENTRY
• •
• •
• •
TAG ENTRY
3
HIT 3
2
HIT 2
1
HIT 1
HIT 0
0
PA(11–0)
PA(12)
MUX
1
PAGE SIZE
19
PA(31–13)
9
STATUS
29
29
MUX
LINE SELECT
HIT
HIT
DETECT
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