Devices are required to observe a protocol so that the interrupt-request (IRQ) lines can be shared. The PCI bus consists of four interrupt lines, INTA# through INTD#, all of which are offered to each unit. As much as 8 PCI units share precisely the same IRQ line (INTINA# through INTINH#) https://nathanlabsadvisory.com/swift-csp-assessments/