An Instruction Buffer for a Low-Power DSP

An architecture for a low-power asynchronous DSP has been developed, for the target application of GSM (digital cellphone) chipsets. A key part of this architecture is an instruction buffer which both provides storage for prefetched instructions and performs hardware looping. This requires low latency and a reasonably fast cycle time, but must also be designed for low power. A design is presented based on a word-slice FIFO structure. This avoids the problems of input latency and power consumption associated with linear micropipeline FIFOs, and the structure lends itself relatively easily to the required looping behaviour. The latency, cycle time and power consumption for this design is compared to that of a simple micropipeline FIFO. The cycle time for the instruction buffer is around three times slower than the micropipeline FIFO. However, the instruction buffer shows an energy per operation of between 48-62% of that for the (much less capable) micropipeline structure. The input to output latency with an empty FIFO is less than the micropipeline design by a factor of ten.