TI486 Microprocessor - Al Kossow's Bitsavers

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Virtual 8086 Mode 2.9 Virtual 8086 Mode Both Real Mode and Virtual 8086 (V86) Mode are supported by the TI486 CPU allowing execution of 8086 application programs and 8086 operating systems. V86 Mode allows the execution of 8086-type applications, yet still permits use of the TI486 protection mechanism. V86 tasks run at privilege level 3. Upon entry, all segment limits are set to FFFFh (64K) as in real mode. 2.9.1 Memory Addressing While in V86 mode, segment registers are used in an identical fashion to Real Mode. The contents of the segment register are shifted left four bits and added to the offset to form the segment base linear address. The TI486 CPU permits the operating system to select which programs use the V86 address mechanism and which programs use protected mode addressing for each task. The TI486 also permits the use of paging when operating in V86 mode. Using paging, the 1-MByte address space of the V86 task can be mapped to anywhere in the 4-GByte linear address space of the TI486 CPU. As in real mode, linear addresses that exceed 1 MByte cause a segment limit overrun exception. The paging hardware allows multiple V86 tasks to run concurrently, and provides protection and operating system isolation. The paging hardware must be enabled to run multiple V86 tasks or to relocate the address space of a V86 task to physical address space greater than 1 MByte. 2.9.2 Protection All V86 tasks operate with the least amount of privilege (level 3) and are subject to all of the TI486 protected mode protection checks. As a result, any attempt to execute a privileged instruction within a V86 task results in a general protection fault. In V86 mode, a slightly different set of instructions is sensitive to the I/O privilege level (IOPL) than in protected mode. These instructions are: CLI, INT n, IRET, POPF, PUSHF, and STI. The INT3, INTO and BOUND variations of the INT instruction are not 10PL sensitive. 2-61
Virtual 8086 Mode 2.9.3 Interrupt Handling To fully support the emulation of an 8086-type machine, interrupts in V86 mode are handled as follows. When an interrupt or exception is serviced in V86 mode, program execution transfers to the interrupt service routine at privilege level 0 (i.e., transition from V86 to protected mode occurs) and the VM bit in the EFLAGS register is cleared. The protected mode interrupt service routine then determines if the interrupt came from a protected mode or V86 application by examining the VM bit in the EFLAGS image stored on the stack. The interrupt service routine may then choose to allow the 8086 operating system to handle the interrupt or may emulate the function of the interrupt handler. Following completion of the interrupt service routine, an IRET instruction restores the EFLAGS register (restores VM = 1) and segment selectors and control returns to the interrupted V86 task. 2.9.4 Entering and Leaving V86 Mode V86 mode is entered from protected mode either by executing an IRET instruction at CPL = 0 or by task switching. If an IRET is used, the stack must contain an EFLAGS image with VM = 1 . If a task switch is used, the TSS must contain an EFLAGS image containing a 1 in the VM bit position. the POPF instruction cannot be used to enter V86 mode since the state of the VM bit is not affected. V86 mode can be exited only as the result of an interrupt or exception. The transition out must use a 32-bit trap or interrupt gate which must point to a non-conforming privilege level 0 segment (DPL = 0), or a 32-bit TSS. These restrictions are required to permit the trap handler to IRET back to the V86 program. 2-62 Programming Interface
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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
Page 44 and 45: Register Set Pointer and Index Regi
Page 46 and 47: Register Set 2.3.1.2 Segment Regist
Page 48 and 49: Register Set 2.3.1.3 Instruction Po
Page 50 and 51: Register Set 2.3.2 System Register
Page 52 and 53: Register Set 2.3.2.1 Control Regist
Page 54 and 55: Register Set 2.3.2.2 Descriptor Tab
Page 56 and 57: Register Set Table 2-6. Segment Des
Page 58 and 59: Register Set During task switching,
Page 60 and 61: Register Set The CCRO register (Tab
Page 62 and 63: Register Set Table 2-9. TI486DLCIE
Page 64 and 65: Register Set Table 2-12. ARR 1-ARR4
Page 66 and 67: Register Set 2.3.2.6 Test Registers
Page 68 and 69: Register Set Table 2-14. TR6 and TR
Page 70 and 71: Address Spaces 2.4 Address Spaces T
Page 72 and 73: Address Spaces 2.4.2 Memory Address
Page 74 and 75: Address Spaces Figure 2-21. Real Mo
Page 76 and 77: Address Spaces Figure 2-24. Paging
Page 78 and 79: Interrupts and Exceptions 2.5 Inter
Page 80 and 81: Interrupts and Exceptions 2.5.3 Int
Page 82 and 83: Interrupts and Exceptions Table 2-2
Page 84 and 85: System Management Mode 2.6 System M
Page 86 and 87: System Management Mode Figure 2-29.
Page 88 and 89: System Management Mode The new SMM
Page 90 and 91: System Management Mode During SMM o
Page 92 and 93: Protection The Current Privilege Le
Page 96 and 97: TI486SLC/E Bus Interface 3-1
Page 98 and 99: Chapter 3 TI486SLC/E Bus Interface
Page 100 and 101: Overview Table 3-1. TI486SLCIE Sign
Page 102 and 103: Overview Table 3-2. Terminal Functi
Page 108 and 109: Overview 3.1.1 Bus Cycle Definition
Page 110 and 111: Overview Table 3-5 shows the state
Page 112 and 113: Functional Timing Figure 3-3. Bus A
Page 114 and 115: Functional Timing 3.2.2.1 Bus Cycle
Page 116 and 117: Functional Timing Non-Pipelined Wai
Page 118 and 119: Functional Timing Because of the de
Page 120 and 121: Functional Timing Pipelined Wait St
Page 122 and 123: Functional Timing Initiating and Ma
Page 124 and 125: Functional Timing Figure 3-12. Comp
Page 126 and 127: Functional Timing Figure 3-13. Inte
Page 128 and 129: Functional Timing Shutdown Indicati
Page 130 and 131: Functional Timing Figure 3-17. Pipe
Page 132 and 133: Functional Timing As shown in Figur
Page 134 and 135: Functional Timing Figure 3-19. Requ
Page 136 and 137: Functional Timing Figure 3-21. Requ
Page 138 and 139: Functional Timing Figure 3-22. 8MI
Page 140 and 141: Functional Timing HALT Initiated Su
Page 142 and 143: 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 4-2. Terminal Functi
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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 Figure 4-23. Requ
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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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U Appendix A TI486 SMM Pro rammer's
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SMM Implementation A.2 SMM Implemen
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Figure A-1. SMM Memory Space Header
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SMM Implementation 6) NMI is the on
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Instruction Summary A.4 Instruction
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Instruction Summary A.4.3 Resume No
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Instruction Summary A.4.6 Save LDTR
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8MI Handler Example A.5 SMI Handler
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8MI Handler Example execute_halt: C
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8MI Handler Example COMMENT A The T
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8MI Handler Example arrl arr2 arr3
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.MODEL SMALL . STACK .386P INCLUDE
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Testing/Debugging SMM Code sgdt COM
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Testing/Debugging SMM Code i*******
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TI486 Power Management Features A.7
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Detection of Tl486 CPU A.9 Detectio
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Detection of SMM Capable Version A.
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i**********************************
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A.11 SMM Feature Comparison SMM Fea
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SMM Instruction Macros COMMENT A Co
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SMM Instruction Macros SMM Instruct
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A.14 Format of Data Used by SVDC/RS
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Altering SMM Code Limits A.1S Alter
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SMM Errata A.16 SMM Errata The foll
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Appendix B TI486 Cache Flush B.1 Ge
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Appendix C TI486 BIOS Modification
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Introduction Some example assembler
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Appendix D Ordering Information 0.1
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~TEXAS INSTRUMENTS Printed in U.S.A
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