Fixed-Point ECU Development with Model-Based Design 2008-01-0744

When developing production software for fixed-point Engine Control Units (ECUs), it is important to consider the transition from floating-point to fixed-point algorithms. Systems engineers frequently design algorithms in floating-point math, usually double precision. This represents the ideal algorithm behavior without much concern for its final realization in production software and hardware. Software engineers and suppliers in mass production environments, however, are concerned with production realities and often need to convert these algorithms to fixed-point math for their integer-only hardware.

A key task is to design scale factors that maximize code efficiency by minimizing the bytes used, while also minimizing quantization effects such that the fixed-point algorithms match the floating-point results within an acceptable numerical margin. This floating- to fixed-point conversion task is tedious, labor intensive, error-prone, and often requires multiple iterations between system and software engineers.

Model-Based Design simplifies fixed-point development by providing tools and workflows that help the conversion process. System engineers doing on-target rapid prototyping for fixed-point ECUs often benefit from automated scaling and workflow assistance to support their initial fixed-point design. Production software engineers benefit from automated scaling as well, but they also require fine grain control over fixed data specification in their modeling environment to work with accumulator word sizes and target-specific optimizations. In addition to providing automated scaling and fine grain data modeling features, Model-Based Design capabilities for fixed-point verification and validation continue to evolve. One example is bit-accurate, fixed-point simulation with automated comparison to embedded software results using processor-in-the-loop testing.

This paper presents Model-Based Design capabilities and tools that support development and verification of fixed-point ECU software used in mass production vehicles.