Intel 80386 manual Reserved Locations, Intierrupts, Shutdown and Halt

80386

3.3 RESERVED LOCATIONS

There are two fixed areas in memory which are re- served in Real address mode: system initialization area and the interrupt table area. Locations OOOOOH through 003FFH are reserved for interrupt vectors. Each one of the 256 possible interrupts has a 4-byte jump vector reserved for it. Locations FFFFFFFOH through FFFFFFFFH are reserved for system initiali- zation.

3.4 INTIERRUPTS

Many of the exceptions shown in Table 2-5 and dis- cussed in section 2.9 are not applicable to Real Mode operation, in particular exceptions 10, 11, 14, will not happen in Real Mode. Other exceptions have slightly different meanings in Real Mode; Table 3-1 identifies these exceptions.

3.5 SHUTDOWN AND HALT

The HLT instruction stops program execution and prevents the processor from using the local bus until restarted. Either NMI, INTR with interrupts enabled (IF = 1), or RESET will force the 80386 out of halt. If interrupted, the saved CS:IP will point to the next instruction after the HLT.

Shutdown will occur when a severe error is detected that prevents further processing. In Real Mode, shutdown can occur under two conditions:

An interrupt or an exception occur (Exceptions 8 or 13) and the interrupt vector is larger than the Interrupt Descriptor Table (i.e. There is not an in- terrupt handler for the interrupt).

A CALL, INT or PUSH instruction attempts to wrap around the stack segment when SP is not even. (e.g. pushing a value on the stack when SP = 0001 resulting in a stack segment greater than

FFFFH)

An NMI input can bring the processor out of shut- down if the Interrupt Descriptor Table limit is large enough to contain the NMI interrupt vector (at least 0017H) and the stack has enough room to contain the vector and flag information (i.e. SP is greater than 0005H). Otherwise shutdown can only be exit- ed via the RESET input.

4.PROTIECTIED MODIE ARCHITIECTURE

4.1 INTRODUCTION

The complete capabilities of the 80386 are unlocked when the processor operates in Protected Virtual Address Mode (Protected Mode). Protected Mode vastly increases the linear address space to four gig- abytes (232 bytes) and allows the running of virtual memory programs of almost unlimited size (64 tera- bytes or 246 bytes). In addition Protected Mode al- lows the 80386 to run all of the existing 8086 and 80286 software, while providing a sophisticated memory management and a hardware-assisted pro- tection mechanism. Protected Mode allows the use of additional instructions especially optimized for supporting multitasking operating systems. The base architecture of the 80386 remains the same, the reg- isters, instructions, and addressing modes described in the previous sections are retained. The main dif- ference between Protected Mode, and Real Mode from a programmer'sview is the increased address space, and a different addressing mechanism.

		Table 3·1
Function	Interrupt	Related	Return
	Number	Instructions	Address Location
Interrupt table limit too small	8	INT Vector is not	Before
		within table limit	Instruction
CS, OS, ES, FF, GS	13	Word memory reference	Before
Segment overrun exception		beyond offset = FFFFH.	Instruction
		An attempt to execute
		past the end of CS segment.
SS Segment overrun exception	12	Stack Reference	Before
		beyond offset = FFFFH	Instruction

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