Android is thought as being yet another operating system! In reality, it is a software platform rather than just an OS; in practical terms, it is an application framework on top of Linux, which facilitates its rapid deployment in many domains. Android was originally designed to be used in mobile computing applications, from handsets to tablets to e-books. But developers are also looking to employ Android in a variety of other embedded systems that have traditionally relied on the benefits of true real-time operating systems performance, boot-up time, real-time response, reliability, and no hidden maintenance costs. In this paper, we present a preliminary conclusion about Android's real-time behavior and performance based on experimental measurements such as thread switch latency, interrupt latency, sustained interrupt frequency, and finally the behavior of mutex and semaphore. All these measurements were done on the same ARM platform (Beagleboard-XM). Our testing results showed that Android in its current state cannot be qualified to be used in real-time environments.

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This paper presents a design and implementation of a Mixed-Criticality System (MCS) extended fromμC/OS III. It is based on a MCS model that uses an adaptive reservation mechanism to cope with the uncertainties in task execution times and to increase the resource utilization in MCS. The implementation takes advantage of the tasks’ recent execution records to predict their required computational resource in the near future and adjusts their reserved budget according to their criticality levels. The designed system focuses on soft real-time tasks. An overrun tolerance algorithm is used to limit the deadline miss ratios between a rise to the task’s actual consumption and the change to the amount of reservation. More than two criticality levels can be handled without introducing obvious additional overhead at each added level. The case study evaluation demonstrates that the reserved resource for each task is always close to its actual consumption; the tasks’ deadline misses are bounded by the different requirements specified by the criticality levels; during overload conditions, high-criticality tasks are guaranteed to have sufficient resource reservation. Although there is still room for improvement if it comes to processing overhead, this research brings some inspirations in both modelling and implementation aspects of MCS.