Gadgets are required to follow a protocol so which the interrupt-request (IRQ) lines can be shared. The PCI bus features 4 interrupt lines, INTA# via INTD#, all of which are offered to each gadget. As much as 8 PCI units share precisely the same IRQ line (INTINA# by means of https://nathanlabsadvisory.com/nist-800-cyber-security-frame-work/