Bisynchronous FIFOs and the FITO Category Mistake: Silicon-Proven Interaction Primitives for Distributed Coordination

A new computer science paper by researcher Paul Borrill, titled 'Bisynchronous FIFOs and the FITO Category Mistake,' makes a provocative claim that could reshape distributed systems theory. The paper surveys over four decades of commercially deployed hardware—specifically bisynchronous FIFOs (First-In, First-Out buffers)—that mediate data transfer between independent clock domains without a shared global clock. Borrill argues this extensive, silicon-proven body of work, from Chapiro's 1984 GALS thesis to NVIDIA's 2015 pausible bisynchronous FIFO, constitutes a direct refutation of the pervasive Forward-In-Time-Only (FITO) assumption. This assumption underpins many timestamp-based coordination protocols like Precision Time Protocol (PTP) and Time-Sensitive Networking (TSN).

The central technical argument is that interaction-based synchronization primitives—handshakes, mutual exclusion, and causal flow control—are not just viable but superior for coordination between independent causal domains. The paper draws a structural parallel between on-chip coordination and the Open Atomic Ethernet (OAE) architecture, identifying the handshake as the fundamental primitive, not the timestamp. This challenges the foundational logic of conventional Ethernet and similar systems. For engineers, the implication is a potential paradigm shift: moving from complex, timestamp-reliant protocols to simpler, proven hardware-inspired interaction models for building more robust and verifiable distributed systems.