The overall important characteristic is the life-time of a communication stream. We aim to develop a SoC for a multimedia terminal where we can assume that the data streams are semi-static and have periodic behavior. This means that for a long period of time subsequent data items of a stream follow the same route. This will last for seconds and more, because a user will listen to its radio or has a phone conversation for a considerable time. However, the control system might change some settings of processes due to changing environmental conditions.
4. Circuit-Switched Revisited
The application analysis of section 3 shows that the amount of expected guaranteed throughput traffic is much larger compared to the amount of best effort traffic. Fundamentally, sharing resources and giving guarantees are conflicting, and efficiently combining guaranteed traffic with best-effort traffic is hard [20]. By using dedicated techniques for both types of traffic we aim for reducing the total area and power consumption. In this paper we concentrate on the architecture for communication of guaranteed throughput traffic. For guaranteed throughput we use reconfigurable circuit switching that create dedicated connections between two processing tiles. The reasons for reconsidering circuit switching instead of using packet switching are:
• The flexibility of packet switching is not needed, because data streams are fixed for a relatively long time. Therefore, a connection between two tiles is required for a long period (e.g. seconds or longer). This connection can be configured by the CCN.
• Large amount of the traffic between tiles will need a guaranteed throughput, which can be easier guaranteed in a circuit-switched connection.
• Current SoC have a large amount of wiring resources that give enough flexibility for streams with different bandwidth demands.
• Circuit switching eases the implementation of asynchronous communication techniques, because data and control can be separated. A control free pipelined asynchronous data stream does not require much design effort.
• The circuit switching has a minimal amount of control in the data pad (e.g. no arbitration). This increases the energy- efficiency per transported bit and the maximum throughput. Further, we see some benefits when guaranteed throughput traffic has to be scheduled:
• Scheduling communication streams over non-time multiplexed channels is easier, because by definition a stream will not have collisions with other communication streams. The Ethereal [5] and SoC BUS [10] routers have large interaction between data streams (both have to guarantee contention free paths). Determining the static time slots table requires considerable effort.
• Because data-streams are physically separated, collisions in the crossbar do not occur. Therefore, we do not need buffering and arbitration in the individual router. An established physical channel can always be used.