User Manual
BCM1250/BCM1125/BCM1125H
10/21/02
B r o a d c o m C o r p o r a t i o n
Document
1250_1125-UM100CB-R
Section 5: L2 Cache
Page
95
.
Figure 13: Cache Management Address
0 0
D
Valid Dirty
Way
Index
39
32 31
28 27
21
18
17 16 15
5
20
4 0
0
26
19
Tag
Tag
ECC
6 bits
32
Bytes
Data
Ecc
10 Bits
Tag
Tag
ECC
6 bits
32
Bytes
Data
Ecc
10 Bits
Tag
Tag
ECC
6 bits
32
Bytes
Data
Ecc
10 Bits
Tag Tag
ECC
6 bits
32
Bytes
Data
Ecc
10 Bits
Data
Data
Data
Data
Way = 00
Way = 01
Way = 10
Way = 11
Written to tag during write
index = 0
.
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index = 4095
ECC_
diag
22
23
index = 2047
Table 54: Management Address
Bits
Use
4:0
Offset (always 0, or treated as such by L2).
16:5
Index. The cache is divided in to sets, each containing four 32 byte lines. These bits select which set is indexed.
The BCM1250 has all 4096 sets, the BCM1125/H has only 2048 so bit 16 is not part of the index.
Bits 16:15 are also written to the tag (they are used as tag bits in 256 KB and 128 KB cache configurations).
18:17
Way. These bits select which of the four lines in a set are accessed.
During management writes these address bits are written to the tag.
19
Dirty. The dirty bit indicates that the line held in the L2 cache contains more recent data than the block in main
memory. If this bit is set the block must be written back to memory before the line can be used for another block.
During management writes this address bit is written to the dirty bit and the tag.
20
Valid. The valid bit indicates that the line contains valid data.
During management writes this address bit is written to the valid bit and tag.
22:21
ECC_diag[1:0]. If this field is nonzero during a management mode access an ECC diagnostic access is
performed. During management writes these address bits are written to the tag.
26:23
During management writes these address bits are written to the tag.
39:27 b0000000011010
(
00_D000_0000
-
00_D7FF_FFFF
) this address range selects management access.
During management writes these address bits are written to the tag.
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