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High-Level Synthesis for SiLago

Advances in Optimization of High-Level Synthesis Tool and Neural Network Algorithms

Time: Thu 2022-10-06 13.00

Location: Ka-Sal C (Sven-Olof Öhrvik), Kistagången 16, Kista

Language: English

Subject area: Information and Communication Technology

Doctoral student: Yu Yang , Elektronik och inbyggda system

Opponent: Professor Madhura Purnaprajna, P.E.S. University

Supervisor: Ahmed Hemani, Elektronik och inbyggda system; Zhonghai Lu, Elektronik och inbyggda system

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QC 20220914


Embedded hardware designs and their automation improve energy and engineering efficiency. However, these two goals are often contradictory. The attempts to improve energy efficiency often come at the cost of engineering efficiency and vice-versa. High-level synthesis (HLS) is a good example of this challenge. It has been researched for more than three decades. Nevertheless, it has not become a mainstream design flow component concerning custom hardware synthesis due to the big efficiency gap between the HLS-generated hardware design and the manual RTL design.

This thesis attempts to address the HLS challenge. We divide the research challenge of improving state-of-the-art HLS into three components: 1) the hardware architecture and its underlying VLSI design style, 2) the design automation algorithms and data structures, and 3) the optimization of the algorithm to be mapped.

The SiLago hardware platform has been reported as a prominent hardware architecture that can deliver ASIC-like efficiency and could be an ideal HLS hardware platform. It has the following features: 1) SiLago embodies parallel distributed two-level control. 2) SiLago blocks are hardened blocks that can create valid VLSI designs by abutment without involving logic or physical synthesis.

Consequently, when targeting the SiLago hardware platform, the SiLago HLS tool generates not a single controller but multiple collaborative controllers, each of which is a hierarchy of two levels. The distributed two-level control scheme poses unique challenges in synchronization and scheduling tasks. Unique data structures and instruction scheduling models are developed for the SiLago HLS tool to support the distributed two-level control scheme. The SiLago HLS tool also generates a valid GDSII macro whose average energy, area, and performance are not estimated but known with post-layout accuracy thanks to the predictable SiLago hardware blocks. Moreover, the SiLago HLS tool is not intended for the end-user. It is designed to develop a library of algorithm implementations used by the application-level synthesis (ALS) tool in the SiLago framework. The application is defined as a hierarchy of algorithms. This library would include algorithms that vary in their function, dimension, and degree of parallelism. The ALS tool explores the design space in terms of number and type of algorithm implementation, rather than arithmetic resources, as HLS tools do.

Algorithms are often developed by domain experts. For efficient implementation in hardware, such algorithms often need to be optimized with the hardware platform in mind. Two algorithm instances have been chosen for demonstration purposes. The first instance is a self-organizing map (SOM) based genome recognition algorithm. The second example concerns a complex model of cortex called Bayesian confidence propagation neural network (BCPNN). As developed by computational neuroscientists, the original model demands too much memory storage and memory access.

This thesis addresses the latter two components because the first component has been addressed in the literature. We will first demonstrate the design of the SiLago HLS tool to support the hardware features like the distributed two-level control system. Moreover, we will use the two complex algorithm instances -- SOM and BCPNN, to demonstrate both general-purpose and algorithm-specific hardware-oriented algorithm optimization techniques. With the research carried out in this thesis, the SiLago HLS framework is greatly improved.