A new approach in microcode optimization

The design flow an development of microcontrolled devices deals with a large number of design decisions which influence the realization costs. Some of these decisions are arbitrary choices between design alternatives with hardly any impact on the hardware structure. An example for such design alternatives is the ordering of data inputs at a multiplexor, which can be permutated without any costs in the data path. But such a reordering changes the control-codes for the multiplexor and may possibly allow a reduction of the size of the microcode. This paper presents an algorithm for microcode optimization which uses recoding of arbitrarily coded fields of the microinstruction. A set of design examples is used to demonstrate improvements achieved with our approach