A Firm Real-Time System Implementation using Commercial Off-the-Shelf Hardware and Free Software

The emergence of multimedia and high-speed networks has expanded the class of applications that combine the timing requirements of hard real-time applications with the need for operating system services typically available only on soft-real time or timesharing systems. These applications, which we describe as firm real-time, currently have no widely-available, low-cost operating system to support them. In this paper we discuss modifications we have made to the popular Linux operating system that give it the ability to support the comparatively stringent timing requirements of these applications, while still giving them access to the full range of Linux services. Using our firm real-time system as a basis, we have developed the ATM Reference Traffic System (ARTS) that is capable of recording and accurately reproducing packet-level ATM traffic streams with timing resolution in microseconds. The effectiveness of this application, as well as the comparative ease with which it was developed, illustrate the performance and utility of our