Saehwa Kim

The Robot Software Communications Architecture (RSCA): QoS-Aware Middleware for Networked Service Robots

The ubiquitous robot companion (URC) project has been recently launched in Korea with an aim of putting networked service robots into practical use in residential environments by overcoming technical challenges of home service robots. Embedded middleware is surely one of such challenges since it has to deal with many critical and difficult problems such as real-time guarantees and software reconfigurability on a heterogeneous, distributed mechatronics system. In this paper, we adopt middleware called SCA from the software defined radio domain and extend it for use in URC robots. We call the end result robot software communications architecture (RSCA). The RSCA provides a standard operating environment for robot applications together with a framework that expedites the development of such applications. The operating environment is comprised of a real-time operating system, communication middleware, and deployment middleware, which collectively form a hierarchical structure. Specifically, the RSCA deployment middleware supports the reconfiguration of component-based robot applications including installation, creation, start, stop, tear-down, and un-installation. Since the original SCA lacks real-time guarantees and QoS support, we have significantly extended it while maintaining backward compatibility so that URC robot developers can use existing SCA tools. We have fully implemented RSCA and performed measurements to quantify its run-time performance. Our implementation clearly shows the viability of RSCA

Tool set implementation for scenario-based multithreading of UML-RT models and experimental validation

This paper presents our tool set implementation for scenario-based multithreading of object-oriented real-time models and an accompanying experimental validation. Our tools enable the automated, schedulability-aware implementation of real-time object-oriented models, exploiting an existing CASE tool. Our implementation is facilitated by (1) our customized runtime system modified to support scenario-based thread execution, (2) a design model template that centralizes the arrival of external inputs, (3) a model analyzer tool, and (4) a model-specific code modifier tool. Our tools simplify design by removing thread-related design concerns from the modeling process, separating design and implementation. We performed validation by conducting experiments that clearly demonstrate the performance improvements that can be gained through our scenario-based implementation: response time improvements for high priority tasks of as much as 70% and a 5-fold decrease in blocking or the elimination of blocking for some tasks.

Integrating real-time synchronization schemes into preemption threshold scheduling

Preemption threshold scheduling (PTS) provides prominent benefits for fixed priority scheduling such as increased schedulability, reduced context switches, and decreased memory requirements. Since such benefits allow for scalable real-time system design, we have adopted it into our automatic implementation synthesis method for real-time object-oriented models. In this paper, we present the integration of real-time synchronization schemes into PTS. Specifically, we investigate how to integrate priority inheritance protocols into preemption threshold scheduling such as the basic priority inheritance protocol and the priority ceiling protocol. In our integrated schemes, (1) the preemption threshold, instead of the priority, of a blocked task is inherited when blocking occurs; and (2) priority ceiling, instead of preemption threshold ceiling is used. We also show that our integrated schemes can minimize worst-case context switches and thus is appropriate for the implementation of real-time object-oriented design models.

Designing Real-Time and Fault-Tolerant Middleware for Automotive Software

Automotive software development poses a great deal of challenges to automotive manufacturers since an automobile is inherently distributed and subject to fault-tolerance and real-time requirements. Middleware is a software layer that can handle the intrinsic complexities of distributed systems and arises as an indispensable run-time platform for automotive systems. This paper explains the concept of middleware by enumerating its functions and categorizes middleware according to adopted communication models. It also extracts five essential requirements of automotive middleware and proposes a middleware design for automotive systems based on the message-oriented middleware (MOM) structure. The proposed middleware effectively addresses the derived requirements and includes many essential features such as real-time guarantee, fault-tolerance, and a global time base

Perfecting preemption threshold scheduling for object-oriented real-time system design: from the perspective of real-time synchronization

In spite of the proliferation of object-oriented design methodologies in contemporary software development, their application to real-time embedded systems has been limited because of the practitioners conservative attitude toward handling timing constraints. In fact, this conservative attitude is well-grounded because traditional priority-based scheduling techniques cannot be straightforwardly integrated into them. The automated implementation from the object-oriented real-time designs usually incurs a large number of tasks which, under traditional priority-based scheduling techniques, does not scale well due to excessive preemption overheads. Recently, preemption threshold scheduling was introduced to reduce run-time multi-tasking overhead while improving schedulability by exploiting non-preemptibility as much as possible. Unfortunately, the preemption threshold scheduling cannot be directly adopted into the object-oriented design methods due to the lack of real-time synchronization.In this paper, we present the essential basis of real-time synchronization for preemption threshold scheduling. Specifically, we integrate the priority inheritance protocol, the priority ceiling protocol, and the immediate inheritance protocol into preemption threshold scheduling. We also provide their schedulability analyses. Consequently, the integrated scheme, which minimizes worst-case context switches, is appropriate for the automated implementation of real-time object-oriented design models.

Schedulability-aware mapping of real-time object-oriented models to multi-threaded implementations

The object oriented design methods and their CASE tools are widely used in practice by many real time software developers. However, object oriented CASE tools require an additional step of identifying tasks from a given design model. Unfortunately, it is difficult to automate this step for a couple of reasons: (1) there are inherent discrepancies between objects and tasks; and (2) it is hard to derive tasks while maximizing real time schedulability, since this problem makes a non-trivial optimization problem. As a result, in practical object oriented CASE tools, task identification is usually performed in an ad hoc manner using hints provided by human designers. We present a systematic, schedulability-aware approach that can help mapping real time object oriented models to multithreaded implementations. In our approach, a task contains a group of mutually exclusive transactions that may possess different periods and deadline. For this new task model, we provide a schedulability analysis algorithm. We also show how the run-time system is implemented and how executable code is generated in our framework. We have performed a case study. It shows the difficulty of the task derivation problem and the utility of the automated synthesis of implementation.

Scenario-based implementation architecture for real-time object-oriented models

This paper presents a scenario-based implementation architecture supporting a method capable of automatically mapping real-time object-oriented models into multi-threaded implementations. To implement the synthesis tool supporting the method, we exploit existing CASE tools that support the object-based implementation architecture. Challenges in our approach are (1) how to embed our implementation model into generated design-model-dependent code and (2) how to implement the model-independent run-time-system library. In our approach, to map each scenario to a thread, we make external messages starting scenarios delivered to their mapped physical thread. The main operation of the thread is (1) waiting for any external message to be delivered and (2) executing a while loop where all internal messages are sent and received. The state transition of an active object is guarded by an object-specific mutex to maintain the run-to-completion semantics. The priority of a thread is dynamically set according to the scheduling attributes of an external message for the thread to process.

SCA-based component framework for software defined radio

SCA (Software Communication Architecture), which has been adopted as a SDR (Software Defined Radio) Forum standard, provides a framework that successfully exploits common design patterns of embedded systems software. However, the SCA is inadequate as a component framework since it does not explicitly specify (1) a component model that defines how to express a component interface and how to implement it, (2) a package model that defines what and how to package in deployment units, and (3) a deployment model that defines the deployment environment and deployment process. We propose a SCA-based component framework for SDR. Specifically, we present: (1) a component model that defines a component as a specialized CORBA object that implements object management functionality, (2) a package model exploiting the existing XML descriptors of the SCA, and (3) a deployment model that defines a SCA-based deployment environment with a boot-up process to restore the deployment state and a deployment process supporting lazy application instantiation and dynamic component replacement.

Dynamic deployment of software defined radio components for mobile wireless internet applications

Software Defined Radio (SDR) is a key enabling technology for mobile wireless Internet. SDR represents unique opportunity to provide Internet connectivity to handheld devices over a limitless range of communication standards. For SDR systems to realize their full potential, they must be reconfigurable through the dynamic deployment of SDR components. However, the current SDR Forum standard, Software Communication Architecture (SCA), is insufficient in this respect since it fails to provide a complete component framework. In this paper, we propose a SCA-based component framework for SDR. Specifically, we present (1) a component model that defines a component as a specialized CORBA object that implements object management functionality, (2) a package model exploiting the existing XML descriptors of the SCA, and (3) a deployment model that defines a SCA-based deployment environment, a boot-up process to restore deployment state, and a deployment process supporting lazy application instantiation and dynamic component replacement. Frameworks that incorporate these improvements will meet the dynamic software deployment needs of next-generation wireless Internet applications.

Automatic implementation of real-time object-oriented models and schedulability issues

The object oriented design methods and their CASE tools are widely used in practice by many real time software developers. However, object oriented CASE tools require an additional step of identifying tasks from a given design model. Task identification is usually performed in an ad-hoc manner using hints provided by human designers. The authors present ongoing research into schedulability-aware, automatic synthesis of multi-threaded implementation of a real time object oriented design. We present several feasible implementation strategies and architectures. We propose our approach to automatic implementation and address schedulability issues involved in our approach.