Stratix V Avalon-ST Interface for PCIe Solutions: User Guide

ID 683093
Date 5/03/2019
Public
Document Table of Contents

7.1.4. Legacy Interrupts

Legacy interrupts mimic the original PCI level-sensitive interrupts using virtual wire messages. The Stratix V signals legacy interrupts on the PCIe link using Message TLPs. The term, INTx, refers collectively to the four legacy interrupts, INTA#, INTB#, INTC# and INTD#. The Stratix V asserts app_int_sts to cause an Assert_INTx Message TLP to be generated and sent upstream. Deassertion of app_int_sts causes a Deassert_INTx Message TLP to be generated and sent upstream. To use legacy interrupts, you must clear the Interrupt Disable bit, which is bit 10 of the Command register. Then, turn off the MSI Enable bit.

The following figures illustrates interrupt timing for the legacy interface. The legacy interrupt handler asserts app_int_sts to instruct the Hard IP for PCI Express to send a Assert_INTx message TLP.

Figure 41. Legacy Interrupt Assertion

The following figure illustrates the timing for deassertion of legacy interrupts. The legacy interrupt handler asserts app_int_sts causing the Hard IP for PCI Express to send a Deassert_INTx message.

Figure 42. Legacy Interrupt Deassertion