Multiple contexts in a multi-ported VLIW register file implementation

The register file is an expensive component in the design of any processor, especially, when considering the additional ports that are needed to support multiple datapaths within a wide-issue VLIW processor. In a recent work, these additional resources were used to dynamically reconfigure the register file to support a dynamically reconfigurable VLIW core. The design can be perceived as a single 8-issue, two 4-issue, or four 2-issue VLIW cores. Consequently, the multi-ported design can operate in different modes, namely as one, two, or four register files, respectively, corresponding to the active number of cores. The implementation of the register file design on FPGAs using Block RAMs still results in unused resources due to the coarseness of the Block RAMs. In this paper, we propose to re-purpose these unused BRAM resources to additionally support multiple contexts next to earliermentioned modes. In this manner, the 8-issue, 4-issue, and 2- issue cores have access to 4, 2, and 1 contexts, respectively. Consequently, we can avoid saving and restoring of the task states in a multi-task environment, turning context switching from a traditionally time-consuming event to an almost instantaneous event. The advantage of this is the reduction of interrupt latency and task switching latency, which are important in real-time and embedded systems. Our results show that our technique can improve interrupt latency by a factor of 17.4x compared to using a software register spill routine, depending on the behavior of the memory system. Likewise, the task switching time can be improved by 6.7x.