Efficient Interfacing of Partially Reconfigurable Instruction Set Extensions for Softcore CPUs on FPGAs


  • Dirk Koch
  • Christian Beckhoff
  • Jim Torresen




Partial Reconfiguration, FPGAs, Custom Instructions, CPU Instruction Set


Swapping just small fractions of the configuration of an FPGA can be very beneficial in many applications. This is in particular useful for reconfiguring the instruction set of embedded soft core processors. In this paper, we will sketch that present design techniques include a substantial overhead for integrating reconfigurable parts into the rest of the system. This overhead can cost more logic resources than the actual module implementations. For removing this overhead, we propose a novel technique to constrain the communication resources between the static system and the partial regions.We will demonstrate for a reconfigurable soft core processor that instructions can be integrated into the system without causing any additional logic overhead for the communication. In addition, we reveal how such systems can be easily implemented with our tool ReCoBus-Builder. Furthermore, we will analyze the overhead in terms of reconfiguration time and present a metric helping to take design decisions.

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Special Section on Best SBCCI2010 Papers