Real Time with a Red Hat Analysis of Standard Linux for Real-Time Simulation

There is no doubt that Linux is a full-featured operating system. Its Unix heritage and tuning for use in large server farms has given it traits that any designer of large-scale systems craves: robust, near-crash-proof operation, high performance, and a native software development environment familiar to any Unix developer. There is also little doubt that standard Linux distributions, such as those from Red Hat and Debian, are unsuitable for hard real-time, deeply embedded applications. Embedded and Real-Time Linux extensions fill that niche but at the expense of many great features of standard Linux such as user/kernel protection, memory protection, a complete set of system services, and full device driver availability. However, most man-in-the-loop simulation systems do not have the toughest requirements of hard real-time embedded systems. There is no need for 1000 Hz sample rates, 20 microsecond interrupt response, or deeply embedded operation. Can standard Linux possibly meet the hard real-time requirements of simulation without losing any of the many Linux advantages? The answer is a resounding “Yes”. This paper details the Research and Development effort that resulted in the use of an ordinary Red Hat Linux distribution as the operating system for real-time training simulators. Real-time determinism is the key. Tests were devised to subject various system configurations to a mix o