A C to HDL compiler for pipeline processing on FPGAs

In this paper, we show a compiler that generates high speed pipeline circuits for loop and recursive programs written in C programming language, which are the most time exhaustive parts in many application problems. The compiler has following features. First, all operations (except for memory accesses) are divided into cascades of 8-bit width (at maximum) operations in order to achieve high speed clock cycle. Second, in order to fulfil the pipeline, variables that have data feedback dependencies between loop cycles are specially scheduled based on several kinds of optimizing techniques. Furthermore, computations of each loop cycle are speculatively started in every clock cycle even if an array on the same memory bank may be accessed more than once in a loop cycle and there may be data feedback dependencies caused by the array accesses. When the array is accessed more than once, the pipeline is stalled while the array access operations are executed sequentially, and when the feedback dependencies are detected, the speculative computations are cancelled, and restarted after the updates of array are finished. Experiments on simple combinatorial programs showed that the pipeline circuits generated by the compiler run about 39-47 MHz on ALTERA EPF10KA serious (which is as fast as hand optimized circuits), and the speed up by the speculative execution is more than two.