This PLA generator is heavily inspired by Bob Mayo's work, but relies on PatchWork for making the actual cell assembly. You can use it interactively, as described in section 4, or access it through its procedural interface from another program. You can thus call it from a PW program to generate a PLA to be incorporated automatically in a larger design.

PWPLA uses a standard set of cells for building the PLA. At least one such library exists at this moment that implements CMOS self-timed precharged PLAs, i.e. the type we'll use in the Dragon chips. This library comes with the df-file. If you plan to build (and share, I hope) your library of cells, these are the guidelines.

You can specify the content of your PLA with a truth table, or a set of boolean equations that uses the input and output names listed under the "Input" and "Outputs" options. If you provide a dump file name, you can get the truth table corresponding to your set of equations.

The truth table is specified in "Berkeley format", i.e. something like

On the left side is the AND plane, where every column represent an input; on the rigth side the OR plane and the outputs. The rows are of course product terms.

This format is not too smart, and we'll probably evolve towards something that incorporates the inputs and outputs names and types.

Boolean equations use only three operators: AND, OR and ~ (i.e. NOT). We all know that this is more than enough. You can also use parentheses and end up each equation with a semi-colon.

The PLA description is a file that contains the following options. Most of them are similar to Mayo's module generator description. Here is an example.

The PLA generator package comes with a complete example including

PLAExample.pla  -- the PLA decription

So just try it. Click the command "Run Make PLA generator", provide the file name PLAExample.pla and you should get a small PLA, free for the taking. Expect a few seconds for a small PLA, and up to two minutes for a large guy like the IFU PhB PLA, which has a hundred inputs+outputs and almost 300 minterms. Of course, using the optimizer will severely increase the response time. Speaking of optimizers, the one in use now is Mayo's version. Don Curry has another one that relies on knowledge of the types of fields, and apparently can perform better. It might become another option.

The interface PWPLA provides the type PLADescription and a set of procedures. Unless you plan to build your own PLA-oid generator, you really just need CreatePLAFromFile and CreatePLA. Comments in the interface should suffice.