
Figure 8-7: MSI-X PBA Table
Pending Bits 0 through 63
Pending Bits 64 through 127
Pending Bits ((N - 1) div 64) × 64 through N - 1
QWORD 0
QWORD 1
QWORD (( N - 1) div 64)
Base
AddressPending Bit Array (PBA)
Base + 1 × 8
Base + ((N - 1) div 64) × 8
4. The IRQ Processor reads the entry in the MSI-X table.
a. If the interrupt is masked by the Vector_Control field of the MSI-X table, the interrupt remains in
the pending state.
b. If the interrupt is not masked, IRQ Processor sends Memory Write Request to the TX slave
interface. It uses the address and data from the MSI-X table. If
Message Upper Address
= 0, the
IRQ Processor creates a three-dword header. If the
Message Upper Address
> 0, it creates a 4-
dword header.
5. The host interrupt service routine detects the TLP as an interrupt and services it.
Related Information
• Floor and ceiling functions
• PCI Local Bus Specification, Rev. 3.0
Legacy Interrupts
Legacy interrupts are signaled on the PCIe link using message TLPs. The message TLPs are generated
internally by the Stratix V Hard IP for PCI Express. The app_int_sts input port controls interrupt
generation. The assertion of app_int_sts causes an Assert_INTA message TLP to be generated and sent
upstream. Deassertion of app_int_sts causes a Deassert_INTA 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 figure illustrates interrupt timing for the legacy interface. In this figure the assertion of
app_int_sts instructs the Hard IP for PCI Express to send a Assert_INTA message TLP.
Figure 8-8: Legacy Interrupt Assertion
clk
app_int_sts
app_int_ack
The following figure illustrates the timing for deassertion of legacy interrupts. The assertion of
app_int_sts instructs the Hard IP for PCI Express to send a Deassert_INTA message.
8-6
Legacy Interrupts
UG-01097_avst
2014.08.18
Altera Corporation
Interrupts
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