參數(shù)資料
型號: AM486DE2
英文描述: Am486DE2 Microprocessor Data Sheet
中文描述: Am486DE2微處理器數(shù)據(jù)表
文件頁數(shù): 36/52頁
文件大小: 1242K
代理商: AM486DE2
36
Am486DE2 Microprocessor
TEST REGISTERS 4 AND 5 MODIFICATIONS
The Cache Test Registers for the Am486DE2 micropro-
cessor are the same test registers (TR3, TR4, and TR5)
provided in earlier Am486DX and DX2 microprocessors.
TR3 is the cache test data register. TR4, the cache test
status register, and TR5, the cache test control register,
operate together with TR3.
When WB/WT meets the necessary setup timing and is
sampled Low on the falling edge of RESET, the proces-
sor is placed in Write-through mode and the test register
function is identical to the earlier Am486 microproces-
sors. Table 10 and Table 11 show the individual bit func-
tions of these registers. “TR4 Definition” on page 36 and
“TR5 Definition” on page 36 provide a detailed descrip-
tion of the field functions.
TR4 Definition
This section includes a detailed description of the bit
fields defined for TR4.
Note:
Bits isted n Table 10 as Not used are not ncluded
in these descriptions.
I
Tag (bits 31–11):Read/Write, always available in
Write-through mode. For a cache write, this is the tag
that specifies the address in memory. On a cache look-
up, this is the tag for the selected entry in the cache.
I
Valid (bit 10):Read/Write. This is the Valid bit for the
accessed entry. On a cache look-up, Valid is a copy
of one of the bits reported in bits 6–3. On a cache-
write in Write-through mode, Valid becomes the new
valid bit for the selected entry and set.
I
LRU (bits 9–7):Read Only, independent of the Ext
bit in TR5. On a cache look-up, these are the three
LRU bits of the accessed set. On a cache write,
these bits are ignored; the LRU bits in the cache are
updated by the pseudo-LRU cache replacement
algorithm. Write operations to these locations have
no effect on the device.
I
Valid (bits 6–3):Read Only. On a cache look-up,
these are the four Valid bits of the accessed set.
Write operations to these locations have no effect on
the device.
TR5 Definition
This section includes a detailed description of the bit
fields in TR5.
Note:
Bits isted n Table 11 as Not used are not ncluded
in the descriptions.
I
Index (bits 10–4):Read/Write. Index selects one of
the 128 sets.
I
Entry (bits 3–2):Read/Write. Entry selects between
one of the four entries in the set addressed by the
Set Select during a cache read or write. During
cache-fill buffer writes or cache-read buffer reads,
the value in the Entry field selects one of the four
doublewords in a cache line.
I
Control (bits 1–0):Read/Write. The control bits
determine which operation is to be performed. The
following is a definition of the control operations:
— 00 = Write to cache fill buffer, or read from cache
read buffer.
— 01 = Perform cache write.
— 10 = Perform cache read.
— 11 = Flush the cache (mark all entries invalid)
Table 10. Test Register (TR4)
31
30–29
28
27–26
25–24
23–22
21–20
19
18
17
16
15–
11
10
9–7
6–3
2–0
EXT = 0
Tag
Valid
LRU
Valid
(rd)
Not
used
Table 11. Test Register (TR5)
31–20
19
18–17
16
15–11
10–4
3–2
1–0
Write-Through
Not used
Index
Entry
Control
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