A Mechanism for Communicating in Dynamically Reconfigurable Embedded Systems
نویسندگان
چکیده
We present a time-bounded state-based communication mechanism for dynamically reconfigurable embedded systems. The mechanism is a single-processor, low-overhead version of the Chimera state-variable mechanism, that was developed for state-based communication in multi-processor environments. The new design is suitable for execution on low-performance embedded processors, uses less memory, and supports dynamic binding, one-to-one, one-to-many, and broadcast capabilities in a time-deterministic manner. The Chimera Project[4] demonstrated the use of state-based communication to create dynamically reconfigurable real-time software objects for a multiprocessor environment. Its state variable (SVAR) mechanism provides the user with operating system services that support transparent time-bounded inter-processor communication for high assurance control systems. The mechanism is fully deterministic, and has guaranteed worst-case waiting and transfer times for shared data. In conjunction with Chimera's port-based object model of real-time software components, it improves predictability and performance by minimizing inter-object dependencies as compared to message-based systems. The mechanism also supports dynamic binding, one-to-one, one-to-many, and broadcast capabilities. The SVAR model of communication is also suitable for creating dynamically reconfigurable software for embedded systems[6]. The characteristics of embedded systems introduce different challenges into the design of an SVAR mechanism , as compared to Chimera's version. In particular, embedded systems usually use lower performance processors with less flexibility, have significant memory and CPU band-width limitations, and timing constraints are often more rigid than those allowed in a multiprocessor environment. The binding of communicating objects must also be fast and time-bounded to support dynamic reconfigurability. Although the Chimera mechanism is very effective for meeting its goals in a multiprocessor environment, it has several shortcomings when applied to embedded systems. Its usage of memory is inefficient, as the local table is a duplicate of the global table, even though a process accesses only a small subset of it. It has larger overhead for locking the table, due to its multiprocessor support. The analysis of the mechanism is specific to a VMEbus hardware environment. Chi-mera's mechanism is also specific to its port-based object model, and only supports two pre-programmed operations, one for reading, one for writing. By redesigning the mechanism, we have made improvements that address all of the above shortcoming, making the SVAR communication practical for embedded systems. The mechanism has also been decoupled from the internals of the Chimera Real-Time Operating System[5], allowing it to be ported to any environment. State-based communication is preferred in embedded systems to provide higher assurability. In a message-based system …
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