Verification of Parameterised FPGA Circuit Descriptions with Layout ...

CHAPTER 3. GENERATING PARAMETERISED LIBRARIES WITH LAYOUT 39
general use of these constructs is that each iteration of the loop need not have the same size
(though it often will), for example the loop statements could themselves contain a conditional.
Additional functions will need to be added to the placement expressions to allow placement
relative to arbitrary loop constructs to be described.
Block instantiations include not just instantiations of individual blocks but also series and
parallel compositions of blocks. Series and parallel compositions must be given their own
layout interpretation to ensure that blocks within a composition are laid out correctly, while
the whole composition itself can be placed using the at (x,y) command.
An important requirement for a truly general Quartz framework is that it must be able to
support the full range of Quartz block parameterisation. Two features of Quartz that differ
from languages like Pebble/VHDL are a particular issue here:
• Quartz blocks are relational and may have multiple possible interpretations in terms of
inputs/outputs. During compilation a single input/output arrangement is selected for
each block however when describing the size of a block in terms of its inputs it is not
always clear which parameters supplied to the block are inputs and which are outputs.
• Variable parameters are not restricted to a particular “generics” region of the block
interface and can be distributed anywhere throughout the block’s domain/range. Fur-
thermore, Quartz blocks can output variables as well as being parameterised by input
variables. The compilation of one block may therefore produce a value which impacts
the compilation of a later block.
Since a block size can depend on any variable parameter it is important that the block size
function should be in terms of all input variables, whether in the domain or range. However,
this is complicated further by polymorphism – which signals are variables and which are
real hardware is not in general known. While a polymorphic variable can not effect the
compilation, and hence size, of the immediate block (otherwise its type would have been
deduced as either int or bool during the type-checking stage), it could be supplied as a
parameter to a higher-order parameter block and (sometimes) affect that block’s size, hence
affecting the calling block’s size indirectly. In order to support this possibility block size
functions must be phrased in terms of all domain and range signals, since any one of them