4
Am5
X
86 Microprocessor
AMD
PRELIMINARY
Table of Contents
1
Connection Diagrams and Pin Designations .........................................................................................8
1.1 168-Pin PGA (Pin Grid Array) Package ..........................................................................................8
1.2 168-Pin PGA Designations (Functional Grouping) .........................................................................9
1.3 208-Pin SQFP (Shrink Quad Flat Pack) Package ........................................................................10
1.4 208-Pin SQFP Designations (Functional Grouping) .....................................................................11
2
Logic Symbol ......................................................................................................................................12
3
Pin Description ....................................................................................................................................13
4
Functional Description ........................................................................................................................18
4.1 Overview .......................................................................................................................................18
4.2 Memory .........................................................................................................................................18
4.3 Modes of Operation ......................................................................................................................18
4.3.1 Real mode ...........................................................................................................................18
4.3.2 Virtual mode ........................................................................................................................18
4.3.3 Protected mode ...................................................................................................................18
4.3.4 System Management mode ................................................................................................18
4.4 Cache Architecture .......................................................................................................................18
4.4.1 Write-Through Cache ..........................................................................................................18
4.4.2 Write-Back Cache ...............................................................................................................18
4.5 Write-Back Cache Protocol ...........................................................................................................19
4.5.1 Cache Line Overview ..........................................................................................................19
4.5.2 Line Status and Line State ..................................................................................................19
4.5.2.1 Invalid .........................................................................................................................19
4.5.2.2 Exclusive ....................................................................................................................19
4.5.2.3 Shared .......................................................................................................................19
4.5.2.4 Modified .....................................................................................................................19
4.6 Cache Replacement Description ..................................................................................................20
4.7 Memory Configuration ...................................................................................................................20
4.7.1 Cacheability .........................................................................................................................20
4.7.2 Write-Through/Write-Back ...................................................................................................20
4.8 Cache Functionality in Write-Back mode ......................................................................................20
4.8.1 Processor-Initiated Cache Functions and State Transitions ...............................................20
4.8.2 Snooping Actions and State Transitions .............................................................................21
4.8.2.1 Difference between Snooping Access Cases ............................................................21
4.8.2.2 HOLD Bus Arbitration Implementation .......................................................................22
4.8.2.2.1 Processor-Induced Bus Cycles ........................................................................22
4.8.2.2.2 External Read ...................................................................................................22
4.8.2.2.3 External Write ...................................................................................................22
4.8.2.2.4 HOLD/HLDA External Access TIming ..............................................................22
4.8.3 External Bus Master Snooping Actions ...............................................................................25
4.8.3.1 Snoop Miss.................................................................................................................25
4.8.3.2 Snoop Hit to a Non-Modified Line ..............................................................................25
4.8.4 Write-Back Case .................................................................................................................25
4.8.5 Write-Back and Pending Access .........................................................................................26
4.8.5.1 HOLD/HLDA Write-Back Design Considerations .......................................................27
4.8.5.2 AHOLD Bus Arbitration Implementation ....................................................................28
4.8.5.3 Normal Write-Back .....................................................................................................28
4.8.6 Reordering of Write-Backs (AHOLD) with BOFF .................................................................29
4.8.7 Special Scenarios For AHOLD Snooping ............................................................................30
4.8.7.1 Write Cycle Reordering due to Buffering ...................................................................30
4.8.7.2 BOFF Write-Back Arbitration Implementation ............................................................32
4.8.8 BOFF Design Considerations ..............................................................................................32
4.8.8.1 Cache Line Fills .........................................................................................................32
4.8.8.2 Cache Line Copy-Backs ............................................................................................32
4.8.8.3 Locked Accesses .......................................................................................................32