Interrupt vector 0 in turn points to the start of the

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Unformatted text preview: segment register instructions LDS and LES. Arithmetic instructions ADD, ADC, SUB, SBB, MUL, IMUL, DIV, IDIV, INC, DEC, CMP, and NEG. Logical instructions AND, OR, XOR, and NOT. 8086 EMULATION • • • • • • • • • • • • • • Decimal instructions DAA, DAS, AAA, AAS, AAM, and AAD. Stack instructions PUSH and POP (to general-purpose registers and segment registers). Type conversion instructions CWD, CDQ, CBW, and CWDE. Shift and rotate instructions SAL, SHL, SHR, SAR, ROL, ROR, RCL, and RCR. TEST instruction. Control instructions JMP, Jcc, CALL, RET, LOOP, LOOPE, and LOOPNE. Interrupt instructions INT n, INTO, and IRET. EFLAGS control instructions STC, CLC, CMC, CLD, STD, LAHF, SAHF, PUSHF, and POPF. I/O instructions IN, INS, OUT, and OUTS. Load effective address (LEA) instruction, and translate (XLATB) instruction. LOCK prefix. Repeat prefixes REP, REPE, REPZ, REPNE, and REPNZ. Processor halt (HLT) instruction. No operation (NOP) instruction. The following instructions, added to P6-family processors (some in the Intel 286 processor and the remainder in the Intel386™ processor), can be executed in real-address mode, if backwards compatibility to the Intel 8086 processor is not required. • • • • • • • • • • • • • Move (MOV) instructions that operate on the control and debug registers. Load segment register instructions LSS, LFS, and LGS. Generalized multiply instructions and multiply immediate data. Shift and rotate by immediate counts. Stack instructions PUSHA, PUSHAD, POPA and POPAD, and PUSH immediate data. Move with sign extension instructions MOVSX and MOVZX. Long-displacement Jcc instructions. Exchange instructions CMPXCHG, CMPXCHG8B, and XADD. String instructions MOVS, CMPS, SCAS, LODS, and STOS. Bit test and bit scan instructions BT, BTS, BTR, BTC, BSF, and BSR; the byte-set-on condition instruction SETcc; and the byte swap (BSWAP) instruction. Double shift instructions SHLD and SHRD. EFLAGS control instructions PUSHF and POPF. ENTER and LEAVE control instructions. 16-5 8086 EMULATION • • • BOUND instruction. CPU identification (CPUID) instruction. System instructions CLTS, INVD, WINVD, INVLPG, LGDT, SGDT, LIDT, SIDT, LMSW, SMSW, RDMSR, WRMSR, RDTSC, and RDPMC. Execution of any of the other Intel Architecture instructions (not given in the previous two lists) in real-address mode result in an invalid-opcode exception (#UD) being generated. 16.1.4. Interrupt and Exception Handling When operating in real-address mode, software must provide interrupt and exception-handling facilities that are separate from those provided in protected mode. Even during the early stages of processor initialization when the processor is still in real-address mode, elementary realaddress mode interrupt and exception-handling facilities must be provided to insure reliable operation of the processor, or the initialization code must insure that no interrupts or exceptions will occur. The Intel Architecture processors handle interrupts and exceptions in real-address mode similar to the way they handle them in protected mode. When a processor receives an interrupt or generates an exception, it uses the vector number of the interrupt or exception as an index into the interrupt table. (In protected mode, the interrupt table is called the interrupt descriptor table (IDT), but in real-address mode, the table is usually called the interrupt vector table, or simply the interrupt table.) The entry in the interrupt vector table provides a pointer to an interrupt- or exception-handler procedure. (The pointer consists of a segment selector for a code segment and a 16-bit offset into the segment.) The processor performs the following actions to make an implicit call to the selected handler: 1. Pushes the current values of the CS and EIP registers onto the stack. (Only the 16 leastsignificant bits of the EIP register are pushed.) 2. Pushes the low-order 16 bits of the EFLAGS register onto the stack. 3. Clears the IF flag in the EFLAGS register to disable interrupts. 4. Clears the TF, RC, and AC flags, in the EFLAGS register. 5. Transfers program control to the location specified in the interrupt vector table. An IRET instruction at the end of the handler procedure reverses these steps to return program control to the interrupted program. Exceptions do not return error codes in real-address mode. The interrupt vector table is an array of 4-byte entries (refer to Figure 16-2). Each entry consists of a far pointer to a handler procedure, made up of a segment selector and an offset. The processor scales the interrupt or exception vector by 4 to obtain an offset into the interrupt table. Following reset, the base of the interrupt vector table is located at physical address 0 and its limit is set to 3FFH. In the Intel 8086 processor, the base address and limit of the interrupt vector table cannot be changed. In the P6-family processors, the base address and limit of the interrupt vector table are contained in the IDTR register and can be changed using the LIDT instruction. (For 16-6 8086 EM...
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This note was uploaded on 06/07/2013 for the course ECE 1234 taught by Professor Kwhon during the Spring '10 term at Berkeley.

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