參數(shù)資料
型號: AMD-640
廠商: Advanced Micro Devices, Inc.
英文描述: 64-Bit Socket 7 Interface, Integrated Write back Cache Controller, System Memory Controller, and PCI Bus Controller.(64位系統(tǒng)控制器(包括高速緩沖存儲器控制器,系統(tǒng)存儲器控制器和PCI總線控制器))
中文描述: 64位Socket 7的接口,集成寫回高速緩沖存儲器控制器,系統(tǒng)內(nèi)存控制器和PCI總線控制器。(64位系統(tǒng)控制器(包括高速緩沖存儲器控制器,系統(tǒng)存儲器控制器和的PCI總線控制器))
文件頁數(shù): 48/159頁
文件大?。?/td> 1900K
代理商: AMD-640
Functional Operation
5-9
21090C/0—June 1997
AMD-640 System Controller Data Sheet
Preliminary Information
Protocol
To simplify system design, the AMD-640 system controller uses
only one cache control bit (the modify bit) rather than the two
bits employed in the MESI (modified, exclusive, shared,
invalid) protocol. In writeback mode there are only three
cache states—invalid, valid, and modified. The modify bit
indicates whether the cache line is valid (cleared) or modified
(set), except when all active tag lines are set, which indicates
the invalid state. Table 5-5 summarizes bit conditions for the
various cache states.
Figure 5-4 shows how cache state transitions occur.
Table 5-4.
Cache Miss Action Taken
Cycle Type
Processor read
Action Taken
1.
The line currently in the cache is written back to DRAM if no
modify bit is used or the modify bit is set.
The entire data line is read from DRAM and written to the cache.
The tag is updated.
The modify bit is reset (writeback/modify bit scheme only).
The requested data is returned to the processor.
2.
3.
4.
5.
Processor write
1.
2.
1.
The data is written to DRAM.
Cache data, tag, and modify bits are unchanged.
The processor is snooped to write back the modified internal
cache line.
Data (all four bytes) are read from DRAM.
Cache data, tag, and modify bits are unchanged.
The processor is snooped to write back the modified internal
cache line.
Data is written to the cache.
Cache data, tag, and modify bits are unchanged.
PCI read
2.
3.
1.
PCI write
2.
3.
Table 5-5.
Cache States vs. Bit Conditions
Cache State
Valid
Modified
Invalid
Modify Bit
0
1
x
Other Tag Lines
Not all 1’s
Not all 1’s
All 1’s
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