Products are required to follow a protocol so which the interrupt-ask for (IRQ) traces could be shared. The PCI bus includes 4 interrupt traces, INTA# by INTD#, all of which are available to each unit. Approximately 8 PCI units share the identical IRQ line (INTINA# by INTINH#) in APIC-enabled x86 https://nathanlabsadvisory.com/soc-1/