System Support

8259 Mode

The 8259 mode handles interrupts IRQ0-IRQ15 in the legacy (AT-system) method using

8259-equivalent logic. Table 4-7 lists the standard source configuration for maskable interrupts and their priorities in 8259 mode. If more than one interrupt is pending, the highest priority (lowest number) is processed first.

Table 4-7.

Maskable Interrupt Priorities and Assignments

Priority

Signal Label

Source (Typical)

 

 

 

1

IRQ0

Interval timer 1, counter 0

 

 

 

2

IRQ1

Keyboard

 

 

 

3

IRQ8-

Real-time clock

 

 

 

4

IRQ9

Unused

 

 

 

5

IRQ10

PCI devices/slots

 

 

 

6

IRQ11

Audio codec

 

 

 

7

IRQ12

Mouse

 

 

 

8

IRQ13

Coprocessor (math)

 

 

 

9

IRQ14

Primary IDE controller

 

 

 

10

IRQ15

Sec. IDE I/F controller (not available on SATA units)

 

 

 

11

IRQ3

Serial port (COM2)

 

 

 

12

IRQ4

Serial port (COM1)

 

 

 

13

IRQ5

Network interface controller

 

 

 

14

IRQ6

Diskette drive controller

 

 

 

15

IRQ7

Parallel port (LPT1)

 

 

 

--

IRQ2

NOT AVAILABLE (Cascade from interrupt controller 2)

 

 

 

 

4-12

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