An optimal warning-zone-length assignment algorithm for real-time and multiple-QoS on-chip bus arbitration

Abstract

In an advanced System-on-Chip (SoC) for real-time applications, the arbiter of its on-chip communication subsystem needs to support multiple QoS criteria while providing a hard real-time guarantee. To fulfill both objectives, the arbitration algorithm must dynamically switch between NonReal-Time (NRT) and Real-Time (RT) modes such that use of the RT mode is minimized to best accommodate the overall QoS criteria. In this article, we define a model for this problem, and propose optimal solutions to its associated problems with static and dynamic warning-zone-length assignment. Compared with previous works, the proposed approach enables a bus arbiter to use much less RT mode in providing a Real-Time (RT) guarantee and, therefore, gives the arbiter more opportunity to employ non-RT modes to achieve better overall QoS. Experimental results show that the proposed approach reduces RT mode usage by as much as 37.1%. Moreover, that reduction in RT mode usage helps cut the execution time by 27.0% when applying our approach to an industrial DRAM controller. Another case study on an AMBA-compliant ultra-high-resolution H.264 decoder IP shows that the proposed approach reduces RT mode usage by 26.4%, which leads to an average reduction of 10.4% in decoding time. Finally, when implementing a 16 master arbiter, it costs only 6.9K and 9.5K gates of overhead using the proposed static and dynamic approach, respectively. Therefore, the proposed approach is suitable for real-time SoC applications.