FPGA processor timing tweaks reduce multiplication stalls significantly
Memory Admission and Result-Retention Sizing in an RV32IMC FPGA Soft Processor
Hardware Architecture
Summary
Multiplying numbers inside small, programmable computer chips can get delayed due to waiting on memory access. The authors studied how changing when and how memory requests are made affects these delays in their RV32IMC soft processor. They found that making data requests slightly earlier can speed up programs by about 18% on average and reduce wasted waiting times. Their method also helps predict how timing adjustments recover performance in different cases. This helps designers decide how to schedule memory requests for faster processing.
What this means in practice
- •For fpga designers: Optimize memory request timing in soft processors to reduce multiplication stalls and improve execution speed.
- •For embedded systems engineers: Use admission and retention sizing methods to tune processor memory interfaces for better performance in resource-constrained devices.
Authors
Yihang Dai, Shuyu Xu, Yinfeng Zhou, Chenglei Peng
Abstract
In FPGA soft processors with shared backing block RAM, memory admission can stall a multiplication after its product has been prepared. We study how admission timing changes result retention in PaceRV, our board-tested five-stage RV32IMC core, using fixed binaries and matched dynamic instructions. Offering data requests one edge earlier reduces geometric-mean Embench cycles by 18.2% and retention opportunities from 375,063 to 4,373. Admission and retention cycle gains are conditional and non-additive. Under slower reads, a 99% capture target selects an 18-edge validity window with registered requests and 28 edges with early requests, although no multiplication matched within both measurement intervals waits longer. A predeclared sizing rule predicts opportunity recovery exactly in all finite tests, including kernels excluded from model development. Independent timing analysis closely estimates execution-cycle savings. The results support choosing admission first, then deciding whether to extend validity and sizing it against an explicit capture or missed-opportunity objective.