Background

There are a lot of different Counter/Timer solutions available on the market. There are some subtle features that many boards will lack that don't make them good matches for applications involving a complex duty cycle.

Counter/Timer Solutions

Concurrent RCIM (Real-Time Counter and Interrupt Module)

Concurrent, the vendor of the popular real-time Linux distribution RedHawk, sells a Counter/Timer solution referred to generically as the RCIM. Concurrent's RCIM is powered not by a dedicated Counter/Timer chip but rather a CPLD (specifically the Lattice ispMACH LC4512V, at least in the case of the RCIM-II, it's likely the other RCIM revisions will also be CPLD-based) which is likely running code developed by Concurrent.

CTS9513 (successor of the AM9513)

The CTS9513 is a modern replacement for the venerable AM9513. The AM9513 is a Counter/Timer chip manufactured by AMD. Discontinued in 1995 it has been described as too complex for its own good, but as we'll later discuss, this complexity is what makes the 9513 a good fit for complex duty cycle applications.

Hardware and software compatible, the only changes the CTS9513 has from the original AM9513 is lower power requirements and support for clocks up to 20 MHz.

The Problem

Most Counter/Timer boards are geared toward frequency based scheduling or simple duty cycle. A count value is loaded into a repeating counter and a clock steps the counter down until it expires at which point it resets to the original count value. The original count value is not changed, and changing it requires the clock to the be stopped and restarted.