For efficiency, the performance of digital CMOS gates is often expressed in terms of empirical models. Both delay and short-circuit power dissipation are sometimes characterized as a function of load capacitance and input signal transition time. However, gate loads can no longer be modeled by purely capacitive loads for high performance CMOS due to the RC metal interconnect effects. This paper presents a methodology for interfacing empirical gate models to reduced order RC interconnect models in terms of a nonlinear iteration procedure. The delay and power are calculated with errors on the same order as those for the original empirical equations. Moreover, a linear equivalent gate model is generated which accurately captures the delays at the interconnect fan-out nodes.

Performance computation for precharacterized CMOS gates with RC loads

The IBM POWER4 processor is a 174-milliontransistor chip that runs at a clock frequency of greater than 1.3 GHz. It contains two microprocessor cores, high-speed buses, and an on-chip memory subsystem. The complexity and size of POWER4, together with its high operating frequency, presented a number of significant challenges for its multisite design team. This paper describes the circuit and physical design of POWER4 and gives results that were achieved. Emphasis is placed on aspects of the design methodology, clock distribution, circuits, power, integration, and timing that enabled the design team to meet the project goals and to complete the design on schedule.

The circuit and physical design of the POWER4 microprocessor

Logic synthesis is the process of automatically generating optimized logic-level representation from a high-level description. With the rapid advances in integrated circuit technology and the resultant growth in design complexity, designers increasingly rely on logic synthesis to shorten the design time while achieving performance objectives. This paper describes the IBM logic synthesis system BooleDozer™, including its organization, main algorithms, and how it fits into the design process. The BooleDozer logic synthesis system has been widely used within IBM to successfully synthesize processor and ASIC designs.

BooleDozer: logic synthesis for ASICs

The traditional purpose of physical synthesis is to perform timing closure , i.e., to create a placed design that meets its timing specifications while also satisfying electrical, routability, and signal integrity constraints. In modern design flows, physical synthesis tools hardly ever achieve this goal in their first iteration. The design team must iterate by studying the output of the physical synthesis run, then potentially massage the input, e.g., by changing the floorplan, timing assertions, pin locations, logic structures, etc., in order to hopefully achieve a better solution for the next iteration. The complexity of physical synthesis means that systems can take days to run on designs with multimillions of placeable objects, which severely hurts design productivity. This paper discusses some newer techniques that have been deployed within IBM's physical synthesis tool called PDS that significantly improves throughput. In particular, we focus on some of the biggest contributors to runtime, placement, legalization, buffering, and electric correction, and present techniques that generate significant turnaround time improvements

Techniques for Fast Physical Synthesis

In this paper, we propose a unified approach to partitioning, floorplanning, and retiming for effective and efficient performance optimization. The integration enables the partitioner to exploit more realistic geometric delay model provided by the underlying floorplan. Simultaneous consideration of partitioning and retiming under the geometric delay model enables us to hide global interconnect latency effectively by repositioning FF along long wires. Under the proposed geometric embedding based performance driven partitioning problem, our GEO algorithm performs multi-level top-down partitioning while determining the location of the partitions. We adopt the concept of sequential arrival time [14] and develop sequential required time in our retiming based timing analysis engine. GEO performs cluster-move based iterative improvement on top of multi-level cluster hierarchy [4], where the gain function obtained from the timing analysis is based on the minimization of cutsize, wirelength, and sequential slack. In our comparison to (i) state-of-the-art partitioner hMetis [9] followed by retiming [11] and simulated annealing based slicing floorplanning [15], and (ii) state-of-the-art simultaneous partitioning with retiming HPM [7] followed by floorplanning [15], GEO obtains 35% and 23% better delay results while maintaining comparable cutsize, wirelength, and runtime results.

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Physical planning with retiming

The paper describes some of the synthesis controls in the BooleDozer synthesis system which are unique in concept and implementation. Rather than attempting to achieve the maximum amount of optimization in the minimum amount of run time, the designer specifies the restructuring level which allows him to specify to what extent the original structure should be preserved. We also describe controls which affect the mapping process. Finally we describe the incremental synthesis feature. The run time can be accurately controlled by a run-time budgeting mechanism. >

In the driver's seat of BooleDozer

This paper presents the timing verification and optimization tools used for the 601, 603, 604 and 620 PowerPC processor designs. The timing verification is done by static timing analysis at the chip level, while the timing optimization is done by synthesis at the macro level. A method for automatically deriving timing constraints for timing optimization is described. >

Timing verification and optimization for the PowerPC processor family

A combinatorial logic optimization is described. The optimization is (in some sense) a dual of earlier global flow optimizations. The optimization leaves the function carried by each signal in the circuit unchanged and thus avoids expensive recomputation of don't care information. The results of experiments performed to evaluate this optimization are also described. >

R.F. Damiano

Papers

In the driver's seat of BooleDozer

Timing verification and optimization for the PowerPC processor family

Dual global flow