Devices are required to abide by a protocol so the interrupt-ask for (IRQ) traces may be shared. The PCI bus involves four interrupt traces, INTA# via INTD#, all of which are offered to every device. Up to 8 PCI gadgets share the identical IRQ line (INTINA# by means of INTINH#) https://nathanlabsadvisory.com/beta-testing-software-applocation/