Dynamic power dissipation on I/O buses is an important issue for high-speed communication between chips. One can use coding techniques to reduce the number of transitions, which will reduce the dynamic power. Bus-invert coding is one popular technique for interchip buses, where the dominant contribution is from the self-capacitance of the wires. This algorithm uses an invert line to signal whether the bus data are in its original or an inverted form. While the method appears to be a greedy algorithm, we show that it is, in fact, an optimal strategy. To do so, we first represent the bus and invert line using a trellis diagram. Then, we show that applying bus-invert coding to a sequence of words gives the same result as would be obtained by using the Viterbi algorithm, which is known to be optimal. We also show that partitioning an M-bit bus into P subbuses and using bus-invert coding on each subbus can be described as applying the Viterbi algorithm on a 2P-state trellis.
Abstract-We present a digital hardware model for ultra wideband channels. The system runs at 80 MHz on a Xilinx Virtex-4 xc4vsx35 FPGA. High-speed arithmetic operations including division, square root, powering and normal random number generator are analyzed and developed for use as basic components in the channel emulator. The design flow is based on Matlab Simulink as the model builder, followed by Xilinx System Generator to transform the Simulink model into a VHDL description which can be synthesized and mapped onto the FPGA device. Speed and area results are given for the synthesized designs.
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