Guoling Han

Application-specific instruction generation for configurable processor architectures

Designing an application-specific embedded system in nanometer technologies has become more difficult than ever due to the rapid increase in design complexity and manufacturing cost. Efficiency and flexibility must be carefully balanced to meet different application requirements. The recently emerged configurable and extensible processor architectures offer a favorable tradeoff between efficiency and flexibility, and a promising way to minimize certain important metrics (e.g., execution time, code size, etc.) of the embedded processors. This paper addresses the problem of generating the application-specific instructions to improve the execution speed for configurable processors. A set of algorithms, including pattern generation, pattern selection, and application mapping, are proposed to efficiently utilize the instruction set extensibility of the target configurable processor. Applications of our approach to several real-life benchmarks on the Altera Nios processor show encouraging performance speedup (2.75X on average and up to 3.73X in some cases).

AutoPilot: A Platform-Based ESL Synthesis System

The rapid increase of complexity in System-on-a-Chip design urges the design community to raise the level of abstraction beyond RTL. Automated behavior-level and system-level synthesis are naturally identified as next steps to replace RTL synthesis and will greatly boost the adoption of electronic system-level (ESL) design. High-level executable specifications, such as C, C++, or SystemC, are also preferred for system-level verification and hardware/software co-design.

Architecture and synthesis for on-chip multicycle communication

For multigigahertz designs in nanometer technologies, data transfers on global interconnects take multiple clock cycles. In this paper, we propose a regular distributed register (RDR) microarchitecture, which offers high regularity and direct support of multicycle on-chip communication. The RDR microarchitecture divides the entire chip into an array of islands so that all local computation and communication within an island can be performed in a single clock cycle. Each island contains a cluster of computational elements, local registers, and a local controller. On top of the RDR microarchitecture, novel layout-driven architectural synthesis algorithms have been developed for multicycle communication, including scheduling-driven placement, placement-driven simultaneous scheduling with rebinding, and distributed control generation, etc. The experimentation on a number of real-life examples demonstrates promising results. For data flow intensive examples, we obtain a 44% improvement on average in terms of the clock period and a 37% improvement on average in terms of the final latency, over the traditional flow. For designs with control flow, our approach achieves a 28% clock-period reduction and a 23% latency reduction on average.

Platform-Based Behavior-Level and System-Level Synthesis

With the rapid increase of complexity in system-on-a-chip (SoC) design, the electronic design automation (EDA) community is moving from RTL (Register Transfer Level) synthesis to behavioral-level and system-level synthesis. The needs of system-level verification and software/hardware co-design also prefer behavior-level executable specifications, such as C or SystemC. In this paper we present the platform-based synthesis system, named xPilot, being developed at UCLA. The first objective of xPilot is to provide novel behavioral synthesis capability for automatically generating efficient RTL code from a C or SystemC description for a given system platform and optimizing the logic, interconnects, performance, and power simultaneously. The second objective of xPilot is to provide a platform-based system-level synthesis capability, including both synthesis for application-specific configurable processors and heterogeneous multi-core systems. Preliminary experiments on FPGAs demonstrate the efficacy of our approach on a wide range of applications and its value in exploring various design tradeoffs.

Instruction set extension with shadow registers for configurable processors

Configurable processors are becoming increasingly popular for modern embedded systems (especially for the field-programmable system-on-a-chip). While steady progress has been made in the tools and methodologies of automatic instruction set extension for configurable processors, the limited data bandwidth available in the core processor (e.g., the number of simultaneous accesses to the register file) becomes a potential performance bottleneck. In this paper we first present a quantitative analysis of the data bandwidth limitation in configurable processors, and then propose a novel low-cost architectural extension and associated compilation techniques to address the problem. The application of our approach results in a promising performance improvement.

Exploring power management in multi-core systems

Power dissipation has become a critical design metric in microprocessor-based system design. In a multi-core system, running multiple applications, power and performance can be dynamically traded off using an integrated power management (PM) unit. This PM unit monitors the performance and power of each core and dynamically adjusts the individual voltages and frequencies in order to maximize system performance under a given power budget (usually set by the operating system). This paper presents a performance and power analysis methodology, featuring a simulation model for multi-core systems that can be easily reconfigured for different scenarios and a PM infrastructure for the exploration and analysis of PM algorithms. Two algorithms have been implemented: one for discrete and one for continuous power modes based on non-linear programming. Extensive experiments are reported, illustrating the effect of power management both at the core and the chip level.

Bitwidth-aware scheduling and binding in high-level synthesis

Many high-level description languages, such as C/C++ or Java, lack the capability to specify the bitwidth information for variables and operations. Synthesis from these specifications without bitwidth analysis may introduce wasted resources. Furthermore, conventional high-level synthesis techniques usually focus on uniform-width resources, thus they cannot obtain the full resource savings even with bitwidth information. This work develops a bitwidth-aware synthesis flow, including bitwidth analysis, scheduling and binding, and register allocation and binding, to exploit the multi-bitwidth nature of operations and variables for area-efficient designs. We also develop lower bound estimation to evaluate the efficiency of our proposed solutions for register allocation and binding. The flow is implemented in the MCAS synthesis system (Cong et al., 2004). Experimental results show that our proposed bitwidth-aware synthesis flow reduces area by 36% and wire-length by 52% on average compared to the uniform-width MCAS flow, while achieving the same performance.

Synthesis of an application-specific soft multiprocessor system

The application-specific multiprocessor System-on-a-Chip is a promising design alternative because of its high degree of flexibility, short development time, and potentially high performance attributed to application-specific optimizations. However, designing an optimal application-specific multiprocessor system is still challenging because there are a number of important metrics, such as throughput, latency, and resource usage, that need to be explored and optimized. This paper addresses the problem of synthesizing the application-specific multiprocessor system to minimize latency and resource usage under the throughput constraint. We employ a novel framework for this problem, similar to that of technology mapping in the logic synthesis domain, and develop a set of efficient algorithms, including labeling, clustering and packing, for efficient generation of the multiprocessor architecture with application-specific optimized latency and resources. Specifically, the result of our algorithm is latency-optimal for directed acyclic task graphs. Application of our approach to the Motion JPEG example on Xilinxs Virtex II Pro platform FPGA shows interesting design tradeoffs.

MC-Sim: an efficient simulation tool for MPSoC designs

The ability to integrate diverse components such as processor cores, memories, custom hardware blocks and complex network-on-chip (NoC) communication frameworks onto a single chip has greatly increased the design space available for system-on-chip (SoC) designers. Efficient and accurate performance estimation tools are needed to assist the designer in making design decisions. In this paper, we present MC-Sim, a heterogeneous multi-core simulator framework which is capable of accurately simulating a variety of processor, memory, NoC configurations and application specific coprocessors. We also describe a methodology to automatically generate fast, cycle-true behavioral, C-based simulators for coprocessors using a high-level synthesis tool and integrate them with MC-Sim, thus augmenting it with the capacity to simulate coprocessors. Our C-based simulators provide on an average 45times improvement in simulation speed over that of RTL descriptions. We have used this framework to simulate a number of real-life applications such as the MPEG4 decoder and litho-simulation, and experimented with a number of design choices. Our simulator framework is able to accurately model the performance of these applications (only 7% off the actual implementation) and allows us to explore the design space rapidly and achieve interesting design implementations.

Architectural Synthesis Integrated with Global Placement for Multi-Cycle Communication

Multiple clock cycles are needed to cross the global interconnectsfor multi-gigahertz designs in nanometer technologies. Forsynchronous design, this requires the consideration of multi-cycleon-chip communication at the high level. In this paper, we presenta new architectural synthesis system integrated with globalplacement, named MCAS (Multi-Cycle Architectural Synthesis),on top of the recently-proposed Regular Distributed Register(RDR) micro-architecture. The RDR architecture provides aregular synthesis platform for supporting multi-cyclecommunication. Novel architectural synthesis algorithms thatintegrate high-level synthesis with global placement have beendeveloped in MCAS, including scheduling-driven placement anddistributed controller generation, etc. Experimental results showthat our methodology can achieve a clock period improvement of31% and a total latency improvement of 24% on averagecompared to the conventional architectural synthesis flow.