Importance

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Abstract

A symmetrical multiprocessing system is provided that includes a central interrupt control unit. The central interrupt control unit is coupled to a plurality of processing units and to a plurality of interrupt sources. The interrupt sources include a plurality of peripheral devices coupled to a first peripheral bus, such as a PCI bus. The interrupt sources also include devices coupled to a second peripheral bus, such as an ISA bus. The central interrupt control unit is operative in two modes. In a first mode, referred to as a pass through mode, interrupts from ISA peripheral devices are provided through an interrupt controller, such as cascaded type 8259 interrupt controllers, to the central interrupt control unit. The central interrupt control unit then passes the interrupt directly to a master processing unit. PCI interrupts are provided through a PCI mapper to other available interrupt inputs of the interrupt controller. The pass through mode advantageously allows backwards compatibility of the system with traditional operating systems such as DOS. During the advanced operating mode, the central interrupt control unit causes the PCI mapper to be disabled. In the advanced mode, interrupts from both PCI devices and ISA devices are provided directly to the central interrupt control unit. Since the PCI mapper is disabled during the advanced mode, additional ISA peripheral devices may be supported within the system without contending with PCI interrupts.

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First Claim