Equipment are required to observe a protocol so which the interrupt-request (IRQ) traces could be shared. The PCI bus involves 4 interrupt strains, INTA# via INTD#, all of which can be obtained to every device. Around eight PCI units share a similar IRQ line (INTINA# via INTINH#) in APIC-enabled x86 https://nathanlabsadvisory.com/nerc-cip/