PCI Arbitration
http://www.motorola.com/computer/literature 4-3
4
8259 Interrupts
There are 15 interrupt requests supported by the Peripheral Bus Controller
(PBC), which is only available if an IPMC761 or IPMC712 is installed.
These 15 interrupts are ISA-type interrupts that are functionall y equivalent
to two 82C59 interrupt controllers. Except for IRQ0, IRQ1, IRQ2,
IRQ8_, and IRQ13, each of the interrupt lines can be configured for either
edge-sensitive mode or level-sensitive mode by programming the
appropriate ELCR registers in the PBC.
There is also support for four PCI interrupts, PIRQA_ through PIRQD_.
The PBC has four PIRQ route control registers to allow each of the PCI
interrupt lines to be routed to any of twelve ISA interrupt lines (IRQ0,
IRQ2, IRQ8_, and IRQ13 are reserved for ISA system interrupts). T hese
active low inputs are used for some of the on-board PCI devices.
Since PCI interrupts are defined as level-sensitive, software must pr ogram
the selected IRQ(s) for level-sensitive mo de. The assignments of the ISA
interrupts supported by the PBC as shown in the following table:
Table 4-2. PBC ISA Interrupt Assignments
PRI PSIO
IRQ
Input
Routed to
ISA
IRQ
Controller
Edge/
Level
Polarity
Interrupt Source
Notes
1 IRQ0 INT1 Edge High Timer 1 / Counter 0 1
2MSK/
IRQ1 IRQ1 Edge High Not Used
3-10 IRQ2 Edge High Cascade Interrupt from
INT2
3RTCX1/
IRQ8_ IRQ8_ INT2 Edge Low ABORT Switch, RTC
4 IRQ9 Level Low Watch Dog 1/2
5 PIRQA_ IRQ10 Level Low LAN (on front)
6 IRQ11 Level Low Internal USB controller 2
7MSDT/
IRQ12 IRQ12 Edge High Not Used
8 PIRQC_ IRQ13 LAN (to rear)