In order to eliminate the costs of proprietary systems and special purpose hardware, many real-time and embedded computing platforms are being built on commodity operating systems and generic hardware. Unfortunately, many such systems are ill-suited to the low-latency and predictable timing requirements of real-time applications. This paper, therefore, focuses on application-specific service technologies for low-cost commodity operating systems and hardware, so that real-time service guarantees can be met. We describe contrasting methods to deploy firstclass services on commodity systems, that are dispatched with low latency and execute asynchronously according to bounds on CPU, memory and I/O device usage. Specifically, we present a "user-level sandboxing" (ULS) mechanism, that relies on hardware protection to isolate applicationspecific services from the core kernel. This approach is compared with a hybrid language and run-time protection scheme called "SafeX", that allows untrusted services to be dynamically linked and loaded into a base kernel. SafeX and ULS have been implemented on commodity Linux systems. Experimental results show that both approaches are capable of reducing service violations (and, hence, better qualities of service) for real-time tasks, compared to traditional user-level methods of service deployment in processprivate address spaces. ULS imposes minimal additional overheads on service dispatch latency compared to SafeX, with the advantage that it does not require applicationspecific services to execute in the trusted kernel domain.
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