5 advanced programmable interrupt controller apic in

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Unformatted text preview: an interrupt or exception handler. When execution of the handler is complete, the processor resumes execution of the interrupted procedure or task. The resumption of the interrupted procedure or task happens without loss of program continuity, unless recovery from an exception was not possible or an interrupt caused the currently running program to be terminated. This chapter describes the processor’s interrupt and exception-handling mechanism, when operating in protected mode. A detailed description of the exceptions and the conditions that cause them to be generated is given at the end of this chapter. Refer to Chapter 16, 8086 Emulation for a description of the interrupt and exception mechanism for real-address and virtual-8086 mode. 5.1.1. Sources of Interrupts The processor receives interrupts from two sources: • • External (hardware generated) interrupts. Software-generated interrupts. 5-1 INTERRUPT AND EXCEPTION HANDLING EXTERNAL INTERRUPTS External interrupts are received through pins on the processor or through the local APIC serial bus. The primary interrupt pins on a P6 family or Pentium® processor are the LINT[1:0] pins, which are connected to the local APIC (refer to Section 7.5., “Advanced Programmable Interrupt Controller (APIC)” in Chapter 7, Multiple-Processor Management). When the local APIC is disabled, these pins are configured as INTR and NMI pins, respectively. Asserting the INTR pin signals the processor that an external interrupt has occurred, and the processor reads from the system bus the interrupt vector number provided by an external interrupt controller, such as an 8259A (refer to Section 5.2., “Exception and Interrupt Vectors”). Asserting the NMI pin signals a nonmaskable interrupt (NMI), which is assigned to interrupt vector 2. When the local APIC is enabled, the LINT[1:0] pins can be programmed through the APIC’s vector table to be associated with any of the processor’s exception or interrupt vectors. The processor’s local APIC can be connected to a system-based I/O APIC. Here, external interrupts received at the I/O APIC’s pins can be directed to the local APIC through the APIC serial bus (pins PICD[1:0]). The I/O APIC determines the vector number of the interrupt and sends this number to the local APIC. When a system contains multiple processors, processors can also send interrupts to one another by means of the APIC serial bus. The LINT[1:0] pins are not available on the Intel486™ processor and the earlier Pentium® processors that do not contain an on-chip local APIC. Instead these processors have dedicated NMI and INTR pins. With these processors, external interrupts are typically generated by a system-based interrupt controller (8259A), with the interrupts being signaled through the INTR pin. Note that several other pins on the processor cause a processor interrupt to occur; however, these interrupts are not handled by the interrupt and exception mechanism described in this chapter. These pins include the RESET#, FLUSH#, STPCLK#, SMI#, R/S#, and INIT# pins. Which of these pins are included on a particular Intel Architecture processor is implementation dependent. The functions of these pins are described in the data books for the individual processors. The SMI# pin is also described in Chapter 12, System Management Mode (SMM). MASKABLE HARDWARE INTERRUPTS Any external interrupt that is delivered to the processor by means of the INTR pin or through the local APIC is called a maskable hardware interrupt. The maskable hardware interrupts that can be delivered through the INTR pin include all Intel Architecture defined interrupt vectors from 0 through 255; those that can be delivered through the local APIC include interrupt vectors 16 through 255. All maskable hardware interrupts can be masked as a group. Use the single IF flag in the EFLAGS register (refer to Section 5.6.1., “Masking Maskable Hardware Interrupts”) to mask these maskable interrupts. Note that when interrupts 0 through 15 are delivered through the local APIC, the APIC indicates the receipt of an illegal vector. 5-2 INTERRUPT AND EXCEPTION HANDLING SOFTWARE-GENERATED INTERRUPTS The INT n instruction permits interrupts to be generated from within software by supplying the interrupt vector number as an operand. For example, the INT 35 instruction forces an implicit call to the interrupt handler for interrupt 35. Any of the interrupt vectors from 0 to 255 can be used as a parameter in this instruction. If the processor’s predefined NMI vector is used, however, the response of the processor will not be the same as it would be from an NMI interrupt generated in the normal manner. If vector number 2 (the NMI vector) is used in this instruction, the NMI interrupt handler is called, but the processor’s NMI-handling hardware is not activated. Note that interrupts generated in software with the INT n instruction cannot be masked by the IF flag in the EFLAGS register. 5.1.2. Sources...
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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 University of California, Berkeley.

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