Jaesoo Lee

The robot software communications architecture (RSCA): embedded middleware for networked service robots

In this paper, we present a robot middleware technology named robot software communications architecture (RSCA) for its use in networked home service robots. The RSCA provides a standard operating environment for the robot applications together with a framework that expedites the development of such applications. The operating environment is comprised of a real-time operating system, a communication middleware, and a deployment middleware. Particularly, the deployment middleware supports the reconfiguration of component-based robot applications including installation, creation, start, stop, tear-down, and un-installation. In designing RSCA, we have adopted a middleware called SCA from the software defined radio domain and extend it since the original SCA lacks the real-time guarantees and appropriate event services. We have fully implemented RSCA and performed measurements to quantify its run-time performance. Our implementation clearly shows the viability of RSCA

Q-SCA: Incorporating QoS support into software communications architecture for SDR waveform processing

The Software Communications Architecture (SCA) defined by Joint Tactical Radio Systems (JTRS) is the de facto standard middleware currently adopted by the Software Defined Radio (SDR) Forum, and is widely accepted as a viable solution to reconfigurable component-based distributed computing for adaptive wireless terminals and base stations. While SDR is heavily involved in real-time signal processing, the current SCA lacks QoS capabilities in terms of both QoS specification and enforcement. In this paper, we propose Q-SCA (QoS enabled SCA) to address this problem. Specifically, we present an application model for SDR waveform software, and then extend the SCA core framework for QoS specification and enforcement. Q-SCA supports QoS capabilities by (1) providing a QoS descriptor that is backward compatible with SCA’s original domain profiles, (2) offering services for admission control and resource allocation that are used throughout the application instantiation process, and (3) introducing a mechanism to enforce the result of the resource allocation. We have fully implemented Q-SCA and performed measurements to quantify its run-time performance. Our implementation clearly shows the viability of Q-SCA.

Petri Net-Based FTL Architecture for Parametric WCET Estimation via FTL Operation Sequence Derivation

A flash translation layer (FTL) provides file systems with transparent access to NAND flash memory. Although many applications running on it require real-time guarantees, it is difficult to provide tight worst case execution time (WCET) bounds with conventional static WCET analysis since an FTL exhibits a large variance in execution time depending on its runtime state. Parametric WCET analysis could be an effective alternative but it is also challenging to formulate a parametric WCET function for an FTL program because traditional FTL architecture does not properly model the runtime availability of flash resources in its code structure. To overcome such a limitation, we propose Petri net-based FTL architecture where a Petri net explicitly specifies dependencies between FTL operations and the runtime resource availability. It comes with an FTL operation sequencer that derives at runtime the shortest sequence of FTL operations for servicing an incoming FTL request under the current resource availability. The sequencer computes the WCET of the request by merely summing the WCETs of only those FTL operations in the sequence. Our experimental results show the effectiveness of our FTL architecture. It allowed for tight WCET estimation that yielded WCETs shorter by a factor of 54 than statically analyzed ones.

Memory Footprint Reduction with Quasi-Static Shared Libraries in MMU-less Embedded Systems

Despite a rapid decrease in the price of solid state memory devices, system memory is still a very precious resource in embedded systems. The use of shared libraries is known to be effective in significantly reducing memory usage. Unfortunately, many resource-constrained embedded systems lack MMU, making it extremely difficult to support this technique. To address this problem, we propose a novel shared library scheme called the quasi-static shared library. In quasi-static shared libraries, global symbols are bound to pseudo-addresses at linking time and the actual physical addresses are bound at loading time. This scheme is made possible by emulating MMU’s memory mapping feature with a Data Section Base Register (DSBR) and a Data Section Base Table (DSBT). Quasi-static shared libraries do not require symbol tables which take up time and space at runtime. We have implemented the proposed scheme in a commercial ADSL (Asymmetric Digital Subscriber Line) home network gateway and conducted a series of experiments measuring its memory usage and performance overhead. The result is drastic: a 35% reduction in flash memory usage and a 10% reduction in RAM usage. These results were achieved with only a negligible performance penalty of less than 4%. Even though this scheme was applied to uClinux-based embedded systems, it can be used for any MMU-less real-time operating system.

Extending software communications architecture for QoS support in SDR signal processing

The software communications architecture (SCA) is middleware for providing component interfaces and dynamic reconfigurability to software define radio (SDR) modems and it is widely adopted by the SDR forum. Although its main application domains include real-time signal processing, SCA lacks QoS support. We thus propose a QoS-enabled extension of SCA called Q-SCA. Our extended architecture incorporates a new waveform model, extended domain profiles that describe QoS requirements, and a modified application instantiation process that supports both admission control and resource allocation. We show the viability of Q-SCA through full implementation and experiments.

Providing Network Performance Isolation in VDE-Based Cloud Computing Systems

In a cloud computing system, virtual machines owned by different clients are co-hosted on a single physical machine. It is vital to isolate network performance between the clients for ensuring fair usage of the constrained and shared network resources of the physical machine. Unfortunately, the existing network performance isolation techniques are not effective for cloud computing systems because they are difficult to be adopted in a large scale and require non-trivial modification to the network stack of a guest OS. In this paper, we propose a performance isolation-enabled virtual distributed Ethernet (PIE-VDE) to overcome such difficulties. It is a network virtualization software module running on a host OS. It intends to (1) allocate fair share of outgoing link bandwidth to the co-hosted clients and (2) divide a clients share to the virtual machines owned by it in a fair way. Our approach supports full virtualization of a guest OS, ease in wide scale adoption, limited modification to the existing system, low run-time overhead and work-conserving servicing. Experimental results show the effectiveness of the proposed mechanism. Every client received at least 99.5% of its bandwidth share as specified by its weight.

Quasistatic shared libraries and XIP for memory footprint reduction in MMU-less embedded systems

Despite a rapid decrease in the price of solid state memory devices, system memory is still a very precious resource in embedded systems. The use of shared libraries and execution-in-place (XIP) is known to be effective in significantly reducing memory usage. Unfortunately, many resource-constrained embedded systems lack an MMU, making it extremely difficult to support these techniques. To address this problem, we propose a novel shared library technique called a quasi-static shared library and an XIP, both based on our enhanced position independent code technique. In our quasistatic shared libraries, global symbols are bound to pseudoaddresses at linking time and actual physical addresses are bound at loading time. Unlike conventional shared libraries, they do not require symbol tables that take up valuable memory space and, therefore, allow for expedited address translation at runtime. Our XIP technique is facilitated by our enhanced position independent code where a data section can be arbitrarily located. Both the shared library and XIP techniques are made possible by emulating an MMUs memory mapping feature with a data section base register (DSBR) and a data section base table (DSBT). We have implemented these proposed techniques in a commercial ADSL (Asymmetric Digital Subscriber Line) home network gateway equipped with an MMU-less ARM7TDMI processor core, 2MB flash memory, and 16MB RAM. We measured its memory usage and evaluated its performance overhead by conducting a series of experiments. These experiments clearly demonstrate the effectiveness of our techniques in reducing memory usage. The results are impressive: 35% reduction in flash memory usage when using only the shared library and 30% reduction in RAM usage when using the shared library and XIP together. These results were achieved with only a negligible performance penalty of less than 4%. Even though these techniques were applied to uClinux-based embedded systems, they can be used for any MMU-less real-time operating system.

Per-Client Network Performance Isolation in VDE-Based Cloud Computing Servers

In a cloud server where multiple virtual machines owned by different clients are co-hosted, excessive traffic generated by a small group of clients may well jeopardize the quality of service of other clients. It is thus very important to provide per-client network performance isolation in a cloud computing environment. Unfortunately, the existing techniques are not effective enough for a huge cloud computing system since it is difficult to adopt them in a large scale and they often require non-trivial modification to the established network protocols. To overcome such difficulties, we propose per-client network performance isolation using VDE (Virtual Distributed Ethernet) as a base framework. Our approach begins with per-client weight specification and support client- aware fair share scheduling and packet dispatching for both incoming and outgoing traffic. It also provides hierarchical fairness between a client and its virtual machines. Our approach supports full virtualization of a guest OS, wide scale adoption, limited modification to the existing system, low run-time overhead and work-conserving servicing. Our experimental results show the effectiveness of the proposed approach. Every client received at least 99.4% of its bandwidth share as specified by its weight.