Devices are required to abide by a protocol so that the interrupt-ask for (IRQ) traces may be shared. The PCI bus features four interrupt traces, INTA# through INTD#, all of which can be found to each unit. Around 8 PCI gadgets share precisely the same IRQ line (INTINA# through INTINH#) https://nathanlabsadvisory.com/irs-efile-2/