You can enable MSI-X interrupts by turning on Implement MSI-X under the PCI Express/PCI Capabilities heading using the parameter editor. If you turn on the Implement MSI-X option, you should implement the MSI-X table structures at the memory space pointed to by the BARs as part of your Application Layer.
The Application Layer transmits MSI-X interrupts on the Avalon®-ST TX interface. MSI-X interrupts are single dword Memory Write TLPs. Consequently, the Last DW Byte Enable in the TLP header must be set to 4b’0000. MSI-X TLPs should be sent only when enabled by the MSI-X enable and the function mask bits in the Message Control for the MSI-X Configuration register. These bits are available on the tl_cfg_ctl output bus.