Novel efficient on-chip task scheduler for multi-core hard real-time systems

This article presents an efficient hardware architecture of EDF-based task scheduler, which is suitable for hard real-time systems due to the constant response time of the scheduler. The proposed scheduler contains a queue of ready tasks that is based on a new MIN/MAX queue architecture called Heap Queue, which is inspired by Shift Registers, Systolic Arrays, heapsort algorithm, the Rocket Queue architecture and dual-port RAMs. The instructions of the proposed scheduler have throughput of one instruction per two clock cycles regardless of the actual number of tasks managed by the scheduler, and regardless of the scheduler capacity. The developed task scheduler is optimized for low chip area costs, which leads to lower energy consumption. The Heap Queue-based architecture has constant time complexity due to two clock-cycle response time of the instructions and therefore, the architecture is highly deterministic. The scheduler supports CPUs that can execute 1, 2 or 4 tasks simultaneously, and contains an implementation of clever and efficient logic that can handle conflicts caused by the fact that the scheduler is used by all CPU cores at the same time. The proposed scheduler was verified through SystemVerilog UVM-like simulations that applied billions of randomly generated test instructions. Achieved ASIC (28 nm) and FPGA synthesis results are presented and compared. More than 86% of the chip area and 93% of the total power consumption can be saved if Heap Queue architecture is used in hardware implementations of EDF algorithm. Advantages and disadvantages of the proposed task scheduler are discussed through the comparison to the existing solutions.