Pipeline length optimization in a digital asynchronous trigger controller

This report describes the pipelined architecture of an asynchronous controller designed for a trigger board. To evaluate the suitable depth of the pipelines, the controller has been modelled as a priority queuing system. Some useful parameters have been introduced to estimate the optimal configuration in the static and dynamic priority cases. Nowadays, the hardware controllers are realised into programmable components where, usually, the internal memory resources are limited; to save space the design has been addressed towards the pipeline length optimization. Some analytic results have been reported for the static priority queueing system and, furthermore, the dynamic control of the priorities has been added. The implemented service discipline is a rate-controlled priority queueing discipline; the service rate is controlled with a negative feedback. The stability of this control system has been investigated and some parameters have been highlighted to solve the compromise between the minimum average length of the controlled queues and a suitable margin from the instability. The dynamic scheme requires the design of a more sophisticated system controller, but it shows better performances; it allows to reduce the pipeline depth with the same input rate.