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The Unabridged Pentium 4 IA32 Processor Genealogy by Bob Colwell, Tom Shanley

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Task and Processor Priority

Introduction

The Local APIC uses two register values to determine in what order to dispatch user-defined interrupts to the processor's core:

  • The Task Priority Register (TPR).

  • The Processor Priority Register (PPR).

The TPR is written to by the OS while the PPR derives its contents from the TPR and, if a user-defined interrupt is currently being serviced, the priority of that interrupt. In order to determine the eligibility of a user-defined interrupt to interrupt the executing program or the currently executing user-defined interrupt handler, the Local APIC compares the user-defined interrupt's priority to the processor's priority. The following sections describe the TPR, the PPR and the eligibility test.

The Task Priority ...

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