Webinar Focuses on Deterministic RTOS Performance
A technical webinar is promoting best practices for achieving predictable performance in complex real-time operating systems (RTOS). The session focuses on deterministic scheduling and robust partitioning for mixed-criticality systems. These techniques are essential for meeting the stringent timing and safety requirements of standards like DO-178C in modern avionics.
- The ARINC 653 standard is a key software specification for avionics that enables time and space partitioning, allowing multiple applications with different software levels to run on the same hardware. This standard defines an Application Executive (APEX) API to manage partitions, processes, timing, and communication. - Robust partitioning is critical for fault containment and is traditionally achieved with dedicated hardware, a method that becomes more complex with the shift to Integrated Modular Avionics (IMA) and multi-core processors. This partitioning prevents a fault in one application from causing the entire system to fail. - Mixed-criticality systems, which run applications with different safety and security requirements on the same platform, are increasingly used in aerospace to reduce costs, size, weight, and power (SWaP). These systems must ensure that less critical functions, like passenger entertainment, do not interfere with safety-critical ones, such as flight controls. - DO-178C is the primary standard used by certification authorities like the FAA and EASA to approve all commercial software-based aerospace systems. It defines Design Assurance Levels (DALs), from A to E, based on the potential consequences of a software failure, with Level A being the most stringent for flight-critical functions. - The move to multi-core processors in avionics introduces significant certification challenges under DO-178C due to potential interference between cores sharing resources, which can affect the deterministic behavior of applications. Guidance for certifying multi-core systems is provided in documents like CAST-32A and the upcoming AC 20-193 from the FAA. - Several commercial and open-source RTOS vendors provide solutions for the avionics market, including Wind River's VxWorks 653, Green Hills Software's Integrity-178 tuMP, DDC-I's Deos, and the open-source RTEMS. These operating systems offer features designed to meet the strict requirements of avionics standards. - A key challenge in certifying multi-core systems is demonstrating that the worst-case execution time (WCET) of tasks can be reliably determined despite the non-deterministic effects of shared hardware resources. This often requires a combination of precise static analysis and empirical testing to measure and mitigate interference. - The concept of "allowance" is used in robust scheduling to define how much a task's execution can exceed its estimated worst-case time without jeopardizing the deadlines of other tasks, enhancing the system's tolerance to overruns.
