Tin-Chee Lo

Self-timed interface for S/390 I/O subsystem interconnection

A high-speed interface has been designed for interconnection of the S/390® I/O subsystem to the IBM S/390 G5 processor. The self-timed interface (STI) provides high bandwidth, greater communication distances, and simpler timing within the S/390 servers than traditional interfaces. The STI communicates between the memory bus adapter and the expanded S/390 I/O subsystem, which now includes the new S/390 fiber channel offering (FICON™) and other network-based protocols such as ATM, Fast Ethernet, and Gigabit Ethernet. Also new for G5 is the use of STI for the integrated cluster bus (ICB), providing direct links among multiple G5 servers. The STI communicates over cables up to ten meters in length at a clock frequency of 167 MHz. Data is sent at twice the clock frequency (333 MB/s). The hardware implementation comprises specially designed logic macros, differential drivers and receivers, and the cables and connectors. The receive macro accommodates up to three bittimes of skew by retiming each data bit of the interface to the transmitted clock. This paper describes the STI logic, the characteristics of the link, and the transmission and reception of the data (and clock).