Verification of Parameterised FPGA Circuit Descriptions with Layout ...

CHAPTER 5. SPECIALISATION 121
Buffer/Queue
R
(a) General circuit
R
Buffer/Queue
(b) Specialised
R
Buffer/Queue
Additional Control Logic
R R
Additional Control Logic
(c) Parallelised
Figure 5.10: Space freed by specialisation can be used to further parallelise a circuit
clock frequency but hopefully with reduced power consumption due to the reduction in glitch
propagation [85].
Alternatively, if the logic resources required to carry out a computation can be reduced
but the space allocated on the device remains the same then the freed space can be used
for accelerating the computation in other ways. It could even be used to duplicate the
computational unit, increasing throughput if tasks are switched between processors rather
than queueing for a single processor, as illustrated in Figure 5.10. In this diagram, the dotted
box indicates the logic area allocated to the computation, which can be used to implement
either a general processor, a single specialised processor and some unused logic, or multiple
specialised processors with additional control.
This kind of specialisation is not mere constant propagation and requires a higher-level of
designer involvement. Circuit designers can program library blocks to exhibit this kind of
specialisation behaviour, using Quartz conditionals extended with block size constructs to
identify the size of specialised components. This means that a block to implement the system
in Figure 5.10 could generate any number of additional copies of the computational block
depending on the ratio between the size of Rgen and Rspec.
High-level specialisation can also be used to perform constant propagation on a macro-level,
eliminating the need to process the specialisation individually for each primitive block. This
means that the specialisation process can be run more quickly, important for dynamic spe-
cialisation applications where it is necessary to produce a new circuit quickly at run-time.
High-level and primitive-level specialisation can be combined in descriptions so that large
contiguous collections of blocks can be eliminated at the high level while individual blocks in