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Choose an RTOS for high-speed control

Gerardo Garcia

November 25, 2007

Gerardo GarciaNovember 25, 2007

In many cases, a hard real-time solution is required. Know the factors that'll affect your system.

In recent years, the explosion of embedded devices has blurred the line between a genuine real-time operating system (RTOS) and an operating system that can serve an embedded system. Generally speaking, RTOSs are a subset of embedded operating systems. While you can solve many application challenges with an embedded operating system, some challenges can only be solved with the determinism afforded by a hard RTOS.

One of the most important applications that falls in this category is high-speed control. High-speed control is found in a host of devices and systems ranging from medical instruments and packaging machines to vehicle engine simulations.

The most common type of control that requires real-time execution is a closed-loop control system. Closed-loop control systems normally perform three fundamental actions:

• Acquire feedback signals from the system being controlled, often called the plant.

• Perform logic and/or signal processing on the input signals based on a desired behavior.

• Generate output signals that affect the plant, as shown in Figure 1.

View the full-size image

To separate high-speed control systems from all other control applications, consider that high-speed control systems need to operate at loop rates of 1 ms or less, or perform the aforementioned three actions deterministically at a rate of at least 1 kHz. Moreover, these systems must achieve the control-loop rate to avoid mission-critical system failure.

High-speed control systems, therefore, require a hard real-time solution. While performance is absolutely important, high-speed control systems have other requirements. To find the right RTOS for your control applications, you must consider the following factors:

• Performance

• Software development tools

• Debugging

• Control algorithm integration

• Hardware and I/O support

• Code footprint

• Communication

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