Gordon Raymond Chiu

Difficulty of predicting interconnect delay in a timing driven FPGA CAD flow

This paper studies the difficulty of predicting interconnect delay in an industrial setting. Fifty industrial circuits, Alteras Quartus II CAD software, and Alteras Stratix and Stratix II FPGA architectures were used in the study. We show that there is a large amount of inherent randomness in a state-of-the-art FPGA placement algorithm. Thus, it is impossible to predict interconnect delay with a high degree of accuracy. Futhermore, we show that a simple timing model can be used to predict some aspects of interconnect timing with just as much accuracy as predictions obtained by running the placement tool itself. Finally, we examine the benefits of using the simple timing model in a timing driven physical synthesis flow, and attempt to establish an upper bound on these possible gains, given the difficulty of interconnect delay prediction.

The Stratix™ 10 Highly Pipelined FPGA Architecture

This paper describes architectural enhancements in the Altera Stratix? 10 HyperFlex? FPGA architecture, fabricated in the Intel 14nm FinFET process. Stratix 10 includes ubiquitous flip-flops in the routing to enable a high degree of pipelining. In contrast to the earlier architectural exploration of pipelining in pass-transistor based architectures, the direct drive routing fabric in Stratix-style FPGAs enables an extremely low-cost pipeline register. The presence of ubiquitous flip-flops simplifies circuit retiming and improves performance. The availability of predictable retiming affects all stages of the cluster, place and route flow. Ubiquitous flip-flops require a low-cost clock network with sufficient flexibility to enable pipelining of dozens of clock domains. Different cost/performance tradeoffs in a pipelined fabric and use of a 14nm process, lead to other modifications to the routing fabric and the logic element. User modification of the design enables even higher performance, averaging 2.3X faster in a small set of designs.

Predicting Interconnect Delay for Physical Synthesis in a FPGA CAD Flow

This paper studies the prediction of interconnect delay in an industrial setting. Industrial circuits and two industrial field-programmable gate-array (FPGA) architectures were used in this paper. We show that there is a large amount of inherent randomness in a state-of-the-art FPGA placement algorithm. Thus, it is impossible to predict interconnect delay with a high degree of accuracy. Furthermore, we show that a simple timing model can be used to predict some aspects of interconnect timing with just as much accuracy as predictions obtained by running the placement tool itself. Using this simple timing model in a two-phase timing driven physical synthesis flow can both improve quality of results and decrease runtime. Next, we present a metric for predicting the accuracy of our interconnect delay model and show how this metric can be used to reduce the runtime of a timing driven physical synthesis flow. Finally, we examine the benefits of using the simple timing model in a timing driven physical synthesis flow, and attempt to establish an upper bound on these possible gains, given the difficulty of interconnect delay prediction.

Mapping arbitrary logic functions into synchronous embedded memories for area reduction on FPGAs

This work describes a new mapping technique, RAM-MAP, that identifies parts of circuits that can be efficiently mapped into the synchronous embedded memories found on field programmable gate arrays (FPGAs). Previous techniques developed for mapping into asynchronous embedded memories cannot be used because modern FPGAs do not have asynchronous embedded memories. After technology mapping, an area-prediction cost function is used to guide the selection of logic cones to be placed in embedded memories. Extra logic is added to compensate for missing asynchronous functionality on the synchronous memories. Experiments conducted on Alteras Stratix device family indicate that this embedded memory mapping technique can provide an average area reduction of 6.2% and up to 32.5% on a large set of industrial designs. A small architecture change that increases the size of the FPGA fabric by 0.05% can increase the average area reduction to 14.1% and up to 59.1% on the same design set