The interrupt_out pin can be configured to send interrupts based on the settings of the Interrupt Mask register. The interrupt_out pin signals interrupts to devices attached to the memory mapped AXI4 side of the bridge. The MSI interrupt defined in the Interrupt Mask & Interrupt Decode registers is used to indicate the receipt of a Message Signaled Interrupt only when the bridge is operating in Root Port mode (C_INCLUDE_RC=1).