Improving Technology Mapping for And-Inverter-Cones
Martin Thümmler, Shubham Rai and Akash Kumar
Chair for Processor Design, CfAED Technische Universität Dresden, Germany
ABSTRACT
AND-inverter-cones (AICs), proposed in 2012, offer a suitable alternative to Look-Up-Tables (LUTs) as the basic building block for FPGAs. They support tapping of multiple side outputs and are intrinsically fracturable which favours reduction of logic duplication. Unlike k-inputs LUTs, their area scales linearly with the number of inputs. Technology mapping is one of the crucial tasks to realize the full power of AIC-based FPGAs. However, the current state-of-the-art implementations suffers two main drawbacks as they do not account for the AIC properties fully: (i) The required time set for each node is suboptimal in the context of AIC and that impairs the mapping quality; (ii) they rely on priority cuts, which are unnecessarily runtime-intensive in the context of AIC mapping. To improve the mapping quality, we propose and proof a new method to calculate the maximal required time for each node purely based on its graph depth and height. We propose an asymptotically runtime-optimal inmemory direct cut selection method which leads to similar area numbers ( ˜ 1% area overhead) as our reference priority cut implementation. Combining these improvements with a second area recovery round leads to a final area reduction of 16.4% and 3% for the MCNC and VTR benchmarks respectively as compared to our reference implementation of the latest known technology mapper, while leaving the delay unaltered.
