The arbiter may perhaps take away GNT# at any time. A device that loses GNT# might full its present-day transaction, but may not begin a single (by asserting FRAME#) Except if it observes GNT# asserted the cycle prior to it starts. PCI gives separate memory and memory-mapped I/O port address https://nathanlabsadvisory.com/forensic-audit-cyber-forensics/