This paper examines runtime decisions to configure hardware accelerators or execute in software. Traditionally, reconfigurable FPGAs are reconfigured on-demand with the hardware accelerator, as it is needed by the application. If the software kernel which the hardware kernel replaces is available too, then more sophisticated decision making on reconfigurations may lead to improved execution time and reduced power consumption. The temporal locality algorithm is proposed for applications where individual kernels dominate during differing execution modes. The kernel correlation algorithm is proposed for applications where sequences of kernels are invoked in regular patterns. SystemC simulation is used to compare these two scheduling algorithms against the on-demand policy. Both timing and power consumption results are presented. They indicate that a fairly large reconfiguration time is required for configuration scheduling to be beneficial.

The performance of various access control protocols for bit-serial local area computer network (LACN) rings is studied. Applications in which mnessage packets are of fixed length and shorter than the total inherent propagation delay around the ring are the focus of attention. Token, slotted, and static and dynamic insertion rings are included in the study. In all cases, the transmitting station is responsible for removing its transmitted packet from the ring. Under this type of removal rule, it is possible for the stations of all types of ring structures to execute their access control algorithms with only a short fixed in-line delay in each station. The insertion rings dynamically switch longer delays (insertion registers) into the ring when they are transmitting a packet. The transmitter-remove rule operates in such a way that hogging of the ring transmission facility by a subset of stations cannot occur. Expressions that approximate average transfer time as a function of utilization are derived for all ring types and are checked by simulation. The expressions are found to be quite accurate at low ring utilization levels, which is the case of most importance for LACN's; but some of them exhibit significant errors at high utilization levels. For the assumed, short-packet environment, it is found that token rings exhibit the slowest transfer times, while dynamic insertion rings are fastest.

TORNET is an experimental local area computer network presently being designed and built in the Computer Group Laboratory of the Department of Electrical Engineering at the University of Toronto. The network consists of a number of local rings, each attached to a central ring. The local rings employ a variation on the slotted-ring format that uses a limited insertion technique to achieve reasonable response times for character traffic among many devices and small computers. Two fixed-length packet formats (one byte or 128 bytes of data) are used on the local rings. Only the longer format is used on the central ring which generally provides record level access to shared specialized equipment.