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S5320 – PCI Match Maker: Mailbox Overview

Revision 5.03 – June 14, 2006

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DS1656

105

Data Sheet

Mailbox Interrupts

Although polling status is useful in some cases, polling requires continuous actions by the processor. Mailbox inter-

rupt capabilities are provided to avoid much of the processor overhead required by continuously polling status bits.

The Add-On and PCI interface can each generate interrupts on the incoming mailbox condition and/or the outgoing

mailbox condition. These can be individual enabled/disabled. A specific byte in the incoming mailbox and outgoing

mailbox is identified to generate the interrupt(s). The tasks required to setup the mailbox interrupts are as follows:

Enabling PCI Mailbox Interrupts:

1. Enable PCI outgoing mailbox interrupts. A specific byte within the outgoing mailboxes is identified to assert

INTA# when read by the Add-On interface.

2. Enable PCI incoming mailbox interrupts. A specific byte within the incoming mailboxes is identified to assert

INTA# when written by the Add-On interface.

Enabling Add-On Mailbox Interrupts:

1. Enable Add-On outgoing mailbox interrupts. A specific byte within the outgoing mailboxes is identified to

assert IRQ# when read by the PCI interface.

2. Enable Add-On incoming mailbox interrupts. A specific byte within the incoming mailboxes is identified to

assert IRQ# when written by the PCI interface.

With either the Add-On or PCI interface, these two steps can be performed with a single access to the appropriate

Once interrupts are enabled, the interrupt service routine must access the mailboxes and clear the interrupt

source. A particular application may not require all of the steps shown. For instance, a design may only use the

incoming mailbox interrupts and not require support for the outgoing mailbox interrupts. The interrupt service rou-

tine tasks are as follows:

INTCSR

Bit 4

Enable outgoing mailbox interrupts

INTCSR

Bits 1:0

Identify mailbox byte to generate interrupt

INTCSR

Bit 12

Enable incoming mailbox interrupts

INTCSR

Bits 9:8

Identify mailbox byte to generate interrupt

AINT

Bit 12

Enable outgoing mailbox interrupts

AINT

Bits 9:8

Identify mailbox byte to generate interrupt

AINT

Bit 4

Enable incoming mailbox interrupts

AINT

Bits 1:0

Identify mailbox byte to generate interrupt

CS5320 Datasheet(PDF) 105 Page - Applied Micro Circuits Corporation

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