TI486 Microprocessor - Al Kossow's Bitsavers

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Appendix C TI486 BIOS Modification Guide C.1 Introduction In order to reap full benefit from the TI486 microprocessors, the system BIOS should be modified to support the internal registers that control the on-chip cache and other extra features. This Appendix serves as a guide to some of the changes that need to be considered, and includes sample assembler code for controlling the cache. There are three main areas of consideration that will be discussed in relation to the internal cache registers: • Power-on and hard reset • Protected-mode to real-mode switching • Soft reseVCTRL-ALT-DEL In each case, the state of the CPU cache registers and when and how to change their values must be known. C.1.1 Power-On and Hard Reset In these two cases, the system will be booted into the operating system. Due to the reset line to the CPU going active, the internal cache will be disabled, making the CPU act much like a 386. At some point the cache must be turned on before the as is booted. A convenient time to turn on the cache may be during final chip set initialization, understanding that the cache should remain off during memory sizing. Many BlOSs provide the user an option to disable the system cache using the setup screen. As most user cache control options are stored in non-volatile RAM, the flag responses, and potentially other flags, should be checked before turning the cache on. C-1
Introduction C.1.2 Protected-Mode to Real-Mode Switching Protected-mode to real-mode switching can be implemented to handle cases where the as has been booted, applications have been running, and the CPU needs to be reset to switch from protected mode to real mode. The objective is to switch CPU modes and jump back into the as or application at some saved return address. Because the CPU was reset, the internal cache wll have been disabled. Before returning control to the application the cache should be turned back on, but only if it was on before the reset occurred, This is accomplished by checking the cache enable flag in the non-volatile RAM, to see if the user enabled caching from the setup screen. However, if the BIOS allows the user to turn off the cache by a hot-key combination (perhaps as part of speed switching), other checks may need to be performed to see if the cache should be turned back on. C.1.3 Soft Reset/CTRL-ALT-DEL The objective of a soft reset is to reset the system and reboot the as, similar to power-on and hard-reset, but a hard reset of the CPU is not generated. Thus, the CPU's internal cache is not disabled (if it was on). This can have a negative impact on memory sizing code, such as generating memory size mismatch errors. In this situation, disable the internal cache and enable it prior to booting, if enabled by the user in setup. C.1.4 Turning On and Off the Internal Cache When the TI486 internal cache is turned on or off, the following guidelines should be observed: 1) Turn off interrupts - CLI 2) Turn off cache using CRO bit 30 and flush using WBINVD 3) Manipulate cache registers 4) Turn on cache and flush using WBINVD 5) Turn on interrupts - STI The above sequence ensures that the process is not interrupted until complete and that no cache coherency issues arise when the cach is turned back on. When manipulating the cache registers it is a good idea to explicitly set each register instead of relying on default values. C-2 TI486 BIOS Modification Guide
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.TEXAS INSTRUMENTS TI486 Microproce
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TI486 Microprocessor Reference Guid
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Preface Read This First About This
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About This Manual Appendix D Orderi
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Contents 1 Product Overview .......
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Contents 5.5 AC Characteristics . .
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1-1 TI486SLC/E Functional Block Dia
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Figures 4-27 SUSP Initiated Suspend
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Tables 5-3 Absolute Maximum Ratings
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Product Overview 1-1
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Chapter 1 Product Overview Features
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1.2 Differences Between the TI486SL
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Tl486SLCIE Overview Figure 1-2. TI4
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Tl486DLCIE Overview 1.4 TI486DLC/E
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TI486DLCIE Overview The TI486DLC/E
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Power Management / System Managemen
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Programming Interface 2-1
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Chapter 2 In this chapter, the inte
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Processor Initialization Table 2-1.
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Instruction Set Overview 2.2 Instru
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Register Set 2.3 Register Set There
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Register Set Pointer and Index Regi
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Register Set 2.3.1.2 Segment Regist
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Register Set 2.3.1.3 Instruction Po
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Register Set 2.3.2 System Register
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Register Set 2.3.2.1 Control Regist
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Register Set 2.3.2.2 Descriptor Tab
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Register Set Table 2-6. Segment Des
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Register Set During task switching,
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Register Set The CCRO register (Tab
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Register Set Table 2-9. TI486DLCIE
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Register Set Table 2-12. ARR 1-ARR4
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Register Set 2.3.2.6 Test Registers
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Register Set Table 2-14. TR6 and TR
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Address Spaces 2.4 Address Spaces T
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Address Spaces 2.4.2 Memory Address
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Address Spaces Figure 2-21. Real Mo
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Address Spaces Figure 2-24. Paging
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Interrupts and Exceptions 2.5 Inter
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Interrupts and Exceptions 2.5.3 Int
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Interrupts and Exceptions Table 2-2
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System Management Mode 2.6 System M
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System Management Mode Figure 2-29.
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System Management Mode The new SMM
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System Management Mode During SMM o
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Protection The Current Privilege Le
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Virtual 8086 Mode 2.9 Virtual 8086
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TI486SLC/E Bus Interface 3-1
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Chapter 3 TI486SLC/E Bus Interface
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Overview Table 3-1. TI486SLCIE Sign
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Overview Table 3-2. Terminal Functi
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Overview 3.1.1 Bus Cycle Definition
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Overview Table 3-5 shows the state
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Functional Timing Figure 3-3. Bus A
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Functional Timing 3.2.2.1 Bus Cycle
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Functional Timing Non-Pipelined Wai
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Functional Timing Because of the de
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Functional Timing Pipelined Wait St
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Functional Timing Initiating and Ma
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Functional Timing Figure 3-12. Comp
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Functional Timing Figure 3-13. Inte
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Functional Timing Shutdown Indicati
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Functional Timing Figure 3-17. Pipe
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Functional Timing As shown in Figur
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Functional Timing Figure 3-19. Requ
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Functional Timing Figure 3-22. 8MI
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Functional Timing HALT Initiated Su
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Functional Timing 3.2.12 Float Figu
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TI486DLC/E Bus Interface 4-1
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Chapter 4 TI486DLC/E Bus Interface
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Overview Table 4-1. TI486DLCIE SIgn
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Overview Table 4-6. Signal States D
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Overview 4.1.2 Power Management 4.1
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Functional Timing 4.2 Functional Ti
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Functional Timing The TI486DLC/E da
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Functional Timing Non-Pipelined Rea
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Functional Timing Initiating and Ma
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Functional Timing Figure 4-8. Faste
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Functional Timing Figure 4-9. Vario
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Functional Timing Once a pipelined
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Functional Timing 4.2.3 Bus Cycles
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Functional Timing Pipelined Cycles
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Functional Timing LOCK is activated
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Functional Timing 4.2.6 Halt and Sh
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Functional Timing Figure 4-17. Pipe
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Functional Timing Figure 4-19. Non-
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Functional Timing The TI486DLC/E sa
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Functional Timing 4.2.9 Hold Acknow
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Functional Timing 4.2.10 Coprocesso
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Functional Timing 4.2.12 Power Mana
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Functional Timing Stopping the Inpu
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Electrical Specifications 5-1
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Chapter 5 Electrical Specifications
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ElectricalConnecnons It is recommen
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Recommended Operating Conditions 5.
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DC Electrical Characteristics Table
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AC Characteristics Figure 5-2. TI48
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AC Characteristics Table 5-9. AC Ch
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AC Characteristics Table 5-11. AC C
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____ AC Characteristics 5.5.3 RESET
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Mechanical Specifications 6-1
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Chapter 6 Mechanical Specifications
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Pin Assignments Table 6-1. TI486SLC
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Pin Assignments Figure 6-3. TI486DL
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Package Dimensions 6.2 Package Dime
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Thermal Characteristics 6.3 Thermal
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Instruction Set 7-1
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Chapter 7 Instruction Set This sect
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Instruction Fields 7.2 Instruction
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Instruction Fields 7.2.5 reg Field
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Instruction Fields Table 7-7. mod r
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Instruction Fields 7.2.11 sreg3 Fie
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Clock Count Summary 7.4 Clock Count
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--- --;.J -L 01 Table 7-17. Instruc
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I . ~ -.....J Table 7-17. Instructi
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Table 7-17. Instructions, Opcodes,
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-....J N (J.) Table 7-17. Instructi
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I I i I i Table 7-17. Instructions,
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...... ...... '" Table 7-17. Instru
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-....J N co Table 7-17. Instruction
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"-.I ~ Table 7-17. Instructions, Op
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Page 266 and 267: U Appendix A TI486 SMM Pro rammer's
Page 268 and 269: SMM Implementation A.2 SMM Implemen
Page 270 and 271: Figure A-1. SMM Memory Space Header
Page 272 and 273: SMM Implementation 6) NMI is the on
Page 274 and 275: Instruction Summary A.4 Instruction
Page 276 and 277: Instruction Summary A.4.3 Resume No
Page 278 and 279: Instruction Summary A.4.6 Save LDTR
Page 280 and 281: 8MI Handler Example A.5 SMI Handler
Page 282 and 283: 8MI Handler Example execute_halt: C
Page 284 and 285: 8MI Handler Example COMMENT A The T
Page 286 and 287: 8MI Handler Example arrl arr2 arr3
Page 288 and 289: .MODEL SMALL . STACK .386P INCLUDE
Page 290 and 291: Testing/Debugging SMM Code sgdt COM
Page 292 and 293: Testing/Debugging SMM Code i*******
Page 294 and 295: TI486 Power Management Features A.7
Page 296 and 297: Detection of Tl486 CPU A.9 Detectio
Page 298 and 299: Detection of SMM Capable Version A.
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Page 302 and 303: A.11 SMM Feature Comparison SMM Fea
Page 304 and 305: SMM Instruction Macros COMMENT A Co
Page 306 and 307: SMM Instruction Macros SMM Instruct
Page 308 and 309: A.14 Format of Data Used by SVDC/RS
Page 310 and 311: Altering SMM Code Limits A.1S Alter
Page 312 and 313: SMM Errata A.16 SMM Errata The foll
Page 314 and 315: Appendix B TI486 Cache Flush B.1 Ge
Page 318 and 319: Introduction Some example assembler
Page 320 and 321: Appendix D Ordering Information 0.1
Page 322: ~TEXAS INSTRUMENTS Printed in U.S.A
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