MPC8540 datasheet(449/1302 Pages) FREESCALE

449 / 1302 page

Functional Description

MPC8540 PowerQUICC III Integrated Host Processor Reference Manual, Rev. 1

Freescale Semiconductor

10-45

vector associated with the interrupt source to the interrupt handler routine. The handler can further

vector to different branches of interrupt handling accordingly.

Note that reading IACK also negates the interrupt signal to the processor. See Section 10.3.7.4,

“Processor Interrupt Acknowledge Register (IACK),” for more details.

The internal in-service register (ISR) tracks all interrupts that have caused int to be asserted and

that have received an IACK cycle. An interrupt is considered in-service from the time its vector is

read (through an IACK cycle) until the end of interrupt (EOI) register is written, generating what

the PIC considers an EOI signal.

10.4.1.1 Interrupt Source Priority

Each interrupt source is assigned a priority value of 0–15 through its corresponding vector/priority

vector/priority is greater than the priority programmed into the current task priority register,

CTPR. Setting a source priority to zero inhibits that interrupt. Likewise, setting the CTPR value

to 15 disables all interrupts directed to the int signal.

The PIC unit services simultaneous interrupts occurring with the same priority according to the

following order:

1. MSG0–MSG3

2. IPI0–IPI3

3. Timer0–timer3

4. IRQ[0:11]

5. Internal0–internal31

For example, if MSG0, MSG2, and IPI0 have the same priority and generate simultaneous

interrupts, they are serviced in the following order:

1. MSG0

2. MSG2

3. IPI0

10.4.1.2 Processor Current Task Priority

The CTPR is set by system software to indicate the relative importance of the task running on the

processor. The processor does not receive interrupts with a priority level equal to or lower than its

current task priority. Therefore setting the current task priority to 15 for a particular processor

prevents the delivery of any interrupt to the processor.

MPC8540 Datasheet(PDF) 449 Page - Freescale Semiconductor, Inc