EMERALDS (Extensible Microkernel for Embedded, ReAL-time, Distributed Systems) is a real-time microkernel designed for small-memory embedded applications. These applications must run on slow (15-25 MHz) processors with just 32-128 kbytes of memory, either to keep production costs down in mass produced systems or to keep weight and power consumption low. To be feasible for such applications, the OS must not only be small in size (less than 20 kbytes), but also have low overhead kernel services. Unlike commercial embedded OSs which rely on carefully optimized code to achieve efficiency, EMERALDS takes the approach of redesigning the basic OS services of task scheduling, synchronization, communication, and system call mechanism by using characteristics found in small-memory embedded systems, such as small code size and a priori knowledge of task execution and communication patterns. With these new schemes, the overheads of various OS services are reduced 20-40 percent without compromising any OS functionality.

The Controller Area Network (CAN) is being widely used in real-time control applications such as automobiles, aircraft, and automated factories. In this pacer, we present the mixed traffic scheduler (MTS) for CAN, which provides higher schedulability than fixed-priority schemes like deadline-monotonic (DM) while incurring less overhead than dynamic earliest-deadline (ED) scheduling. We also describe how MTS can be implemented on existing CAN network adapters such as Motorola's TouCAN. In previous work, we had shown MTS to be far superior to DM in schedulability performance. In this paper, we present implementation overhead measurements showing that processing needed to support MTS consumes only about 5 to 6 percent of CPU time. Considering its schedulability advantage, this makes MTS ideal for use in control applications.

EMERALDS (Extensible Microkernel for Embedded, ReAL-time, Distributed Systems) is a real-time microkernel designed for small-memory embedded applications. These applications must run on slow (15-25MHz) processors with just 32-128 kbytes of memory, either to keep production costs down in mass-produced systems or to keep weight and power consumption low. To be feasible for such applications, the OS must not only be small in size (less than 20 kbytes), but also have low-overhead kernel services. Unlike commercial embedded OSs which rely on carefully-crafted code to achieve efficiency, EMERALDS takes the approach of re-designing the basic OS services of task scheduling, synchronization, communication, and system call mechanism by using characteristics found in small-memory embedded systems, such as small code size and a priori knowledge of task execution and communication patterns. With these new schemes, the overheads of various OS services are reduced 20-40% without compromising any OS functionality.

Scheduling messages on the Controller Area Network (CAN) corresponds to assigning identifiers (IDs) to messages according to their priorities. In this paper we present the mixed traffic scheduler (MTS), which provides higher schedulability than fixed-priority schemes like deadline-monotonic (DM) while incurring less overhead than dynamic earliest-deadline (ED) scheduling. Through simulations, we compare the performance of MTS with that of DM and ED* (an imaginary scheduler which works like ED, except it incurs less overhead). Our simulations show that MTS performs much better than DM and at the same level as ED*, except under high loads and tight deadlines, when ED* is superior. I. Introduction Local area networks (LANs) are becoming increasingly popular in industrial automation and other real-time control applications [1], [2]. LANs allow field devices like sensors, actuators, and controllers to be interconnected at low cost --- using less wiring and requiring less maintenance than p...

In any distributed system, messages must be ordered according to their cause-and-effect relation to ensure correct behavior of the system. Causal ordering is also essential for services like atomic multicast and replication. In distributed real-time systems, not only must proper causal ordering be ensured, but message deadlines must be met as well. Previous algorithms which ensure such behavior include the /spl Delta/-protocol family and the MARS approach. However, both these algorithms give large response times by delaying all messages for a fixed period of time. In this paper we show that for small- to medium-sized real-time systems (consisting of a few tens of nodes) as are commonly used for embedded applications, it becomes feasible to extend the h-protocol so that instead of delaying all messages for a fixed period, each message is delayed according to its deadline. Our algorithm requires certain message deadlines to be adjusted by the application designer and we show that for small-scale applications such as those used in embedded systems, this adjustment is feasible and can be automated by the use of proper CAD tools.