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Verification of Parameterised FPGA Circuit Descriptions with Layout ...

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CHAPTER 3. GENERATING PARAMETERISED LIBRARIES WITH LAYOUT 58<br />

The block size inference procedure ensures that all blocks are annotated <strong>with</strong> height and width<br />

expressions. If these expressions have been specified manually then no action is necessary,<br />

however if not the procedure executes the function SB to generate size expressions for the<br />

block.<br />

The verification role <strong>of</strong> the layout processing module will be discussed in Chapter 4. The<br />

actual task <strong>of</strong> converting Quartz layout information to explicit co-ordinates in LE-Pebble is<br />

handled by new stages in the distillation module.<br />

3.7.3 Distillation <strong>of</strong> Size Expressions<br />

The distillation module actually converts Quartz descriptions into Pebble, eliminating higher-<br />

order parameters and other constructs that are not valid in Pebble. This module has been<br />

extended <strong>with</strong> code to compile layout expressions from Quartz into LE-Pebble. This is done<br />

in a recursive descent over expression trees, specifically eliminating height() and width()<br />

references.<br />

Three cases have to be dealt <strong>with</strong>:<br />

1. The height()/width() function refers to a single block <strong>with</strong> domain and range signals<br />

linked into the local environment. In this case the block’s height or width expression is<br />

retrieved and compiled, before replacing the height()/width() function <strong>with</strong> appropriate<br />

substitutions for the correct applied domain/range signals. If the expression refers to<br />

signals internal to the block then these must be replaced <strong>with</strong> fresh identifiers and the<br />

code <strong>with</strong>in the block that defines the values <strong>of</strong> these variables lifted into the current<br />

context.<br />

2. The function refers to a parallel composition <strong>of</strong> blocks. This case is compiled by ap-<br />

plying the size interpretation <strong>of</strong> parallel compositions (function SIσ β) and extracting<br />

expressions for each block in the composition, combining them using either addition<br />

(height) or the max function (width).<br />

3. The function refers to a series composition <strong>of</strong> blocks. In this case a similar operation<br />

must be employed as for parallel compositions however <strong>with</strong> a significant difference.

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