82443MX Datasheet, PDF (128/173 Pages) Intel Corporation – PCIset

82443MX PCIset
NOTE:
Support is not provided for the Secondary IDE channel, so IRQ15 is no longer available externally for
any other purpose. However, the SERIRQ and PCI interrupts can be steered to generate interrupt 15 to
the 8259 interrupt controller.
7.10.1 INTERRUPT CONTROLLER FUNCTIONAL DESCRIPTION
The two 82C59 interrupt controllers provided by the 440MX are cascaded so that 13 external and three
internal interrupts are possible. The master interrupt controller provides IRQ [7:0] and the slave interrupt
controller provides IRQ [15:8] (see Figure 16). The three internal interrupts are used for internal functions only
and are not available to the user. IRQ2 is used to cascade the two controllers together. IRQ0 is used as a
system timer interrupt and is tied to Interval Timer 1, Counter 0. IRQ13 is connected internally to FERR#. The
remaining 13 interrupt lines (IRQ1, IRQ3-IRQ12, IRQ14, and IRQ15) are available for external system
interrupts. Edge or level-sense selection is programmable on an individual channel-by-channel basis.
The Interrupt unit also supports interrupt steering. The 440MX can be programmed to allow the four PCI active
low interrupts (PIRQA#-PIRQD#) to be internally routed to one of 11 interrupts: 3-7, 9-12, 14 or 15.
The Interrupt Controller consists of two separate 82C59 cores. Interrupt Controller 1 (CNTRL-1) and Interrupt
Controller 2 (CNTRL-2) are initialized separately and can be programmed to operate in different modes. The
default settings are: 80x86 Mode, Edge Sensitive (IRQ0-15) Detection, Normal EOI, Non-Buffered Mode,
Special Fully Nested Mode disabled, and Cascade Mode. CNTRL-1 is connected as the Master Interrupt
Controller and CNTRL-2 is connected as the Slave Interrupt Controller.
Note that IRQ13 is generated internally (as part of the coprocessor error support). IRQ12/M is generated
internally (as part of the mouse support) when bit 4 in the XBCS is set to 1. When set to 0, the standard
IRQ12 function is provided and IRQ12 appears externally.
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