Embedded Programmable Logic Core Enhancements for System Bus Interfaces

Programmable logic cores (PLCs) offer a means of providing post-fabrication re-configurability to a SoC design. Circuits implemented in a PLC will, inevitably have lower timing performance and logic density than fixed function circuits. This fundamental mismatch makes the design of the interface between the PLC and the rest of the SoC a challenging problem. In this paper we focus on interfaces between circuits implemented in PLCs and SoC system busses. We demonstrate problems with existing implementation options and then propose modifications to parts of the PLC architecture to enable more efficient system bus interfaces. Our results show that, on average, this modified architecture improves interface timing by 36.4%. reduces CLB usage by 7.9% and improves mutability by 28.8% for circuits that require system bus interfaces. We show that the area overhead is less than 0.5% for circuits that do not require bus interfaces.