Bisynchronous FIFOs -- hardware buffers that mediate data transfer between independent clock domains without a shared global timebase -- have been designed, formally verified, and commercially deployed in silicon for over four decades. We survey this literature from Chapiro's 1984 GALS thesis through Cummings's Gray-code pointer techniques, Chelcea and Nowick's mixed-timing interfaces, Greenstreet's STARI protocol, and the 2015 NVIDIA pausible bisynchronous FIFO, and argue that this body of work constitutes a silicon-proven existence proof against the Forward-In-Time-Only (FITO) assumption that pervades distributed systems. The central claim is that interaction-based synchronization primitives -- handshakes, mutual exclusion, and causal flow control -- can replace timestamp-based coordination at the most demanding levels of digital engineering, directly undermining the FITO assumption in protocols such as PTP, TSN, and conventional Ethernet. We draw a structural parallel between on-chip bisynchronous coordination and the Open Atomic Ethernet (OAE) architecture, and identify the handshake -- not the timestamp -- as the fundamental primitive for coordination between independent causal domains.

翻译：双同步FIFO——一种在没有共享全局时基的独立时钟域间协调数据传输的硬件缓冲器——其设计、形式化验证及商业化流片部署已持续四十余年。本文系统梳理了从Chapiro 1984年GALS论文到Cummings的格雷码指针技术、Chelcea与Nowick的混合时序接口、Greenstreet的STARI协议，直至2015年英伟达可暂停双同步FIFO的相关文献，论证该系列成果构成了对分布式系统中普遍存在的"仅向前时间"（FITO）假设的硅验证反例。核心论点是：基于交互的同步原语——握手协议、互斥机制与因果流控制——能够在数字工程最严苛的层级替代基于时间戳的协调方案，直接颠覆PTP、TSN及传统以太网等协议中的FITO假设。通过揭示芯片级双同步协调与开放原子以太网（OAE）架构的结构同构性，我们指出握手协议——而非时间戳——才是独立因果域间协调的根本原语。