Designing hierarchical hardware for efficient timer handling

The author describes the design of a timer handler coprocessor, the 6pm (Swedish Institute of Computer Science or SICS protocol machine) GMT (general manager of timers). In distributed systems, internode communication needs to have both high throughput and low end-to-end delay. For real-time applications, a guaranteed maximum delay is also important. Special-purpose communication processors (protocol machines) could be used in the nodes to speed up protocol execution. The design of the 6 pm which uses special-purpose coprocessors for well-defined subactivities, is described. This coprocessor is designed for good average and worst-case performance on a high-speed network. Performance estimations based on instructions-counting simulations are given. These simulations show that an implementation of the 6 pm GMT on an 88 K processor will be able to handle all timers on a gigabit network