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Programmable logic cores (PLCs) offer a means of providing post-fabrication reconfigurability to a SoC design. This ability has the potential to significantly enhance the SoC design process by enabling post-silicon debugging, design error correction and post-fabrication feature enhancement. However, circuits implemented in general purpose programmable logic will inevitably have lower timing performance than fixed function circuits. This fundamental mismatch makes it difficult to use the PLC effectively. We address this problem by proposing changes to the structure of the PLC itself; these architectural enhancements enable circuit implementations with high performance interfaces. In previous work we addressed system bus interfaces, in this work we address direct synchronous interfaces. Our results show significant improvement in PLC interface timing, such that interaction with full-speed fixed-function SoC logic is possible. Our enhanced PLCs are able to implement direct synchronous interfaces running at, on average, 662 MHz (compared to 249 MHz in regular programmable logic). We are able to do this without compromising the basic structure or routiblity of the programmable fabric. At the same time, we show that the area overhead for these architectural changes was approximately 1%.