Jupyung Lee

A Ubiquitous Fashionable Computer with an i-Throw Device on a Location-Based Service Environment

The ubiquitous fashionable computer (UFC), introduced in this paper, is a wearable computer that allows people to exploit ubiquitous computing environment in a user-friendly manner. We present the design approach and philosophy of the UFC that is wearable, aesthetic, and intuitive. The UFC supports the interoperability of various communication interfaces among WLAN, Bluetooth and ZigBee devices. We developed a wireless gesture recognition device, called i -Throw, which is small enough to be worn on ones finger like a ring. The UFC, with the help of i -Throw, can control ubiquitous environment using an intuitive hand motion. To explain the practical use of the UFC platform and the user-friendly interaction with ubiquitous environment, we implemented a ubiquitous testbed where multiple UFC users interact with various ubiquitous devices or other UFC users. In addition, we implemented a practical application which makes it possible to exchange the various objects and control ubiquitous devices very easily.

Delayed locking technique for improving real-time performance of embedded Linux by prediction of timer interrupt

In this paper, we propose a new technique, called a delayed locking technique, to improve the real-time performance of embedded Linux. The proposed technique employs the rule that entering a critical section is allowed only if the operation does not disturb the future execution of the real-time application. To execute this rule, we introduce the concepts of timer interrupt prediction and lock hold time acquisition. In addition, we designed and implemented a new high-resolution timer that is simple, yet efficient. We implemented the prototype on Linux 2.4.18. Experimental results show that the worst-case OS latency of real-time process is reduced to 23% of the original one, at the expense of slowdown of the nonreal-time process by 20%. Though we focus only on embedded Linux, our technique is useful for all kinds of real-time operating systems in which the critical section is significantly long.

Interrupt handler migration and direct interrupt scheduling for rapid scheduling of interrupt-driven tasks

In this article, we propose two techniques that aim to minimize the scheduling latency of high-priority interrupt-driven tasks, named the Interrupt Handler Migration (IHM) and Direct Interrupt Scheduling (DIS). The IHM allows the interrupt handler to be migrated from the interrupt handler thread to the corresponding target process so that additional context switch can be avoided and the cache hit ratio with respect to the data generated by the interrupt handler can be improved. In addition, the DIS allows the shortest path reserved for urgent interrupt-process pairs to be laid between the interrupt arrival and target process by dividing a series of interrupt-driven operations into nondeferrable and deferrable operations. Both the IHM and DIS can be combined in a natural way and can operate concurrently. These techniques can be applied to all kinds of interrupt handlers with no modification to them. The proposed techniques not only reduce the scheduling latency, but also resolve the interrupt-driven priority inversion problem. We implemented a prototype in the Linux 2.6.19 kernel after adding real-time patches. Experimental results show that the scheduling latency is significantly reduced by up to 84.2% when both techniques are applied together. When the Linux OS runs on an ARM-based embedded CPU running at 200MHz, the scheduling latency can become as low as 30μs, which is much closer to the hardware-specific limitations. By lowering the scheduling latency, the limited CPU cycles can be consumed more for user-level processes and less for system-level tasks, such as interrupt handling and scheduling.

Prediction-Based Micro-Scheduler: Toward Responsive Scheduling of General-Purpose Operating Systems

In this paper, we propose a novel scheduling technique to improve the responsiveness of a real-time process while maintaining relative execution rates of non-real-time processes, called the prediction-based micro-scheduler. It runs upon an existing macro-scheduler and it conditionally rearranges the scheduling pattern generated by the macro-scheduler based on urgent interval prediction and lock hold time prediction. The rearrangement occurs if one process seeks to enter a long nonpreemptible section and the operation is predicted to significantly disturb the future execution of a real-time process. We implemented the prototype on Linux 2.6.19. Experimental results show that the average OS latency of a real-time process is reduced up to 34 percent of the original one while still maintaining relative execution rates of non-real-time processes. Moreover, the performance degradation caused by the micro-scheduler does not exceed 5 percent.

U-TOPIA: A Ubiquitous Environment with a Wearable Platform, UFC and Its Security Infrastructure, pKASSO

U-TOPIA, introduced in this paper, is an advanced ubiquitous computing environment mainly focusing on a university campus. Research in U-TOPIA spans various components each of which is essential to realize U-TOPIA: from user device hardware/software, user interface, communication technology, indoor/outdoor testbed, middleware to practical applications and security infrastructure. We designed and implemented a wearable platform from the scratch and make use of it as a main user device inside U-TOPIA. In addition to this, as a new user interface, we developed a wireless gesture recognition device, called i-Throw to communicate with U-TOPIA in an intuitive manner. For data communication and location tracking in U-TOPIA, campus-wide indoor and outdoor testbed was deployed. To keep up with secure and dynamic U-TOPIA environment, a new security infrastructure,called pKASSO, and extensible middleware, μ-ware, was developed. Finally, as a practical application for U-TOPIA, we implemented a ubiquitous testbed room where multiple users interact with various ubiquitous devices or other users securely in a user-friendly manner. Integrating these components all together, we show that U-TOPIA can be a realistic role model to improve current paradigm of ubiquitous computing environment one step forward within a few years.