Electronic Design: Motorola

With Linda's help, a parallel program for characterizing large semicustom standard-cell circuits has been implemented by Binay George, Sean Tyler, and Markus Wloka at Motorola Inc.'s Semiconductor Systems Design Technology Center in Tempe, AZ. Called the Entice program (for Energy and timing characterization environment), it is run on networked computers to deliver higher performance and new functions.

Standard cells are circuits that provide specific, pre-defined functionality to chip designers. Used as building blocks for more complex microprocessors, these cells and the larger circuits built from them must be fully simulated with Spice, a linear-circuit simulator, before fabrication. Timing and power characteristics--that is, how quickly the circuits can be cycled and how many watts are consumed during active and idle modes--are primary concerns and must be evaluated for a range of operating temperatures, supply voltages, and other criteria. Full analog simulations of large semicustom designs are extraordinarily time-consuming jobs. Because simulation time grows more than linearly with circuit size and component number, each simulation may take tens of hours or longer to complete on mainframe and minisupercomputer systems.

Motorola's Entice package approximates analog methods to deliver much shorter solution times and higher throughput on such jobs. Instead of performing a sequential simulation of the complete design, Entice performs smaller Spice simulations of each design's component parts in parallel over a workstation network. The performance of the complete design is then approximated by forming sums along those components. The total timing delay, for example, is approximately equal to the sum of timing delays along the longest path in the overall design. For power, total consumption is approximately equal to the sum of the power consumed by all the parts.

Entice's distributed-processing feature dramatically reduces characterization time for standard-cell libraries. Characterization of eight representative cells from the 165-cell Motorola library took more than 127 minutes with Entice on one SparcStation II. On a network of 10 such workstations, the characterization time was reduced to 15 minutes, a speedup of 8.5 times.

Motorola also employs the computational potential of networks to enhance functionality in simulations of very large-scale integrated (VLSI) circuits. Unlike previous characterization systems, Entice incorporates automated file handling facilities and is not limited to specific methodologies.

Standard-cell timing delay and power dissipation, for example, depend on input rise and fall time, fanout capacitive load, temperature, and voltage supply. Entice allows the user to define parameters for all four variables and vary them over ranges of values. According to user preferences, the data obtained may be stored in tabular, piece-wise linear, or polynomial form. These and other features, made practical through the aggregate power of networked systems, make Entice flexible and highly interactive.