A given function can generally be done in half as many clock cycles using twice as much silicon, although name aliases and control hazards (dependence on run-time input data) can limit this. As well as the C/C++ input code we require additional directives over speed, area and perhaps power. The area directives may specify the number of RAMs or how to map arrays into shared DRAM.
Trading (or folding) such time for space is basically a matter of unwinding loops or introducing new loops.
Hazards can limit the amount of unrolling possible, including limited numbers of ports on RAMs and user-set budgets on the number of certain components (FUs) instantiated, such as adders or multipliers.
Unrolling can be:
| 17: (C) 2012-18, DJ Greaves, University of Cambridge, Computer Laboratory. |