Hardware compilation for FPGAs: imperative and declarative approaches for a robotics interface

Illustrates the use of Occam and Ruby in developing a shaft encoder interface. In the joint of a robot arm, a shaft encoder measures the angle of each shaft by reading two output signals generated from photo-sensitive detectors. The light input to these detectors is interrupted by a fine pattern of transparent and opaque regions on a glass disc. Rotating the encoder disc results in two digital pulse streams, and the shaft encoder interface must deduce from these streams the direction of rotation and position. While special-purpose devices such as the Texas Instrument THCT2000 can be used in the interface, the resulting system has a low bandwidth and a high chip-count. The task is to develop a new interface, based on FPGAs, with a higher speed of operation, higher accuracy, additional functionality, smaller physical size, lower development cost, reduced development time, and with increased flexibility