Application Specific FPGA Using Heterogeneous Logic Blocks

Abstract

An Application Specific Inflexible FPGA (ASIF) [12] is an FPGA with reduced flexibility that can implement a set of application circuits which will operate at different times. Application circuits are efficiently placed and routed on an FPGA in such a way that total routing switches used in the FPGA architecture are minimized. Later all unused routing resources are removed from the FPGA to generate an ASIF. An ASIF which is reduced from a heterogeneous FPGA (i.e. containing hard-blocks such as Multipliers, Adders and RAMS etc) is called as a Heterogeneous-ASIF. This work shows that a standard-cell based Heterogeneous-ASIF using Multipliers, Adders and Look-Up-Tables for a set of 10 opencores application circuits is 85% smaller in area than a single driver FPGA using the same blocks, and only 24% larger than the sum of areas of their standard-cell based ASIC version. If the Look-Up-Tables are replaced with a set of repeatedly used hard logic gates (such as AND gate, OR gate, flip-flops etc), the ASIF becomes 89% smaller than the Look-Up-Table based FPGA and 3% smaller than the sum of ASICs. The area gap between ASIF and sum of ASICs can be further reduced if repeatedly used groups of standard-cell logic gates in an ASIF are designed in full-custom. One of the major advantages of an ASIF is that just like an FPGA, an ASIF can also be reprogrammed to execute new or modified circuits, but at a very limited scale. A new CAD flow is presented to map application circuits on an ASIF.