Senior Project - Xident

Field Programmable Gate Arrays (FPGAs) have been around since Xilinx introduced the XC2064 in the mid-1980s. Unlike the PALs (AND - OR arrays with limited OR terms), developed earlier, Xilinx FPGAs consisted of a matrix of logic cells surrounded by vertical and horizontal channels of programmable interconnects. Each cell could be programmed with any arbitrary logic function of the limited number of cell inputs.

The Xilinx FPGAs became popular because they were capable of any logical function and, unlike PALs, they could be scaled to larger and larger arrays. However, the early users had to partition the logic and route the interconnects in addition to defining the logic. This was a new skill for these users. It was difficult to obtain efficient (or even working) designs and caused a lot of disenchantment. Xilinx responded by developing more automated methods to partition, place, and route designs entered via schematics or other means. These automated methods were wildly inefficient in logic density and circuit performance. These techniques could not match the efficiency of a skilled FPGA designer.

In response to this situation, Rhodes Press developed the concept of "Schematic Spreadsheet", which consists of an algorithm to generate a "die-layout background sheet" in a schematic capture CAD program, a means to efficiently generate modules of standard logic functions that can be easily placed on the die-layout background sheet, and finally, an algorithm that extracts the placement information from the schematic elements and passes these attributes to the "fitting" program.

This project required development of a digital database of scanned, published size and I/O location information; development of an algorithm to generate an arbitrary die-layout background sheet for any part type; development of an algorithm to place logic modules in cell locations on the die-layout background sheet; and development of an algorithm to extract placement information from the schematic elements and attach that placement information to the schematic file. The project was implemented in C in an MS-DOS environment.