S. Vicente

AER tools for communications and debugging

Address-event-representation (AER) is a communications protocol for transferring spikes between bio-inspired chips. Such systems may consist of a hierarchical structure with several chips that transmit spikes among them in real time, while performing some processing. To develop and test AER based systems it is convenient to have a set of instruments that would allow to: generate AER streams, monitor the output produced by neural chips and modify the spike stream produced by an emitting chip to adapt it to the requirements of the receiving elements. In this paper we present a set of tools that implement these functions developed in the CAVIAR EU project

A generalization of path following for mobile robots

Several authors have proposed some methods for applying path following in specific cases to mobile robots. When we try to extend the path following approach to the general problem several difficulties arise. We present a generalized technique to apply path following to a mobile robot with nonholonomic constraints. As an application example, we expose the case of mobile robots with a higher degree of manoeuvrability than the typical car-like robots. In particular we consider a robot that can turn around itself making a zero-radius turn; a case still not resolved as far as we know. Finally we propose a suitable control law for this example that ensures asymptotical convergence.

A real-time wireless sensor network for wheelchair navigation

Today, the availability of inexpensive, low power hardware including CMOS cameras and wireless devices make it possible to deploy a wireless sensor network (WSN) with nodes equipped with cameras for a variety of applications. In this paper, we discuss the use of one of these WSNs as a navigation aid for wheelchairs. Instead of having complicated wheelchairs with lots of on-board sensors, we argue that a viable alternative is to have simpler wheelchairs that are able to interact with an intelligent environment so that the wheelchair bases its navigation on its software intelligence, supported by the information sent by external sensors. Many questions have to be investigated, for instance how sensors should be deployed or whether the wireless links would be able to meet our temporal requirements. We describe some of the solutions we adopted, particularly how to implement with Zigbee devices a polling mechanism that allows us to guarantee a real-time secure navigation.

SIRIUS: improving the maneuverability of powered wheelchairs

The indoor maneuverability of powered wheelchairs may be difficult or bothersome in several circumstances. In this paper, we describe an experimental powered wheelchair named SIRIUS, developed at the University of Seville, which introduces some simple but effective navigation aids. Special emphasis is placed on the implementation of recorded trajectory playback and in the shared control modes, i.e., the chairs guiding where both the user and the computer collaborate. Furthermore, SIRIUS is an open platform to essay another kinds of functional or navigational aids, because its hardware architecture is based on a commercial PC. This would permit many devices that are frequently needed by the chair driver to be integrated smoothly into the chair controller.

On the Design of Ambient Intelligent Systems in the Context of Assistive Technologies

The design of Ambient Intelligent Systems (AISs) is discussed in the context of assistive technologies. The main issues include ubiquitous communications, context awareness, natural interactions and heterogeneity, which are analyzed using some examples. A layered architecture is proposed for heterogeneous sub-systems integration with three levels of interactions that may be used as a framework to design assistive AISs.

Soft real-time communications over Bluetooth under interferences from ISM devices

Bluetooth is a suitable technology to support soft real-time applications like multimedia streams at the personal area network level. In this paper, we analytically evaluate the worst-case deadline failure probability of Bluetooth packets under co-channel interference as a way to provide statistical guarantees when transmitting soft real-time traffic using ACL links. We consider the interference from independent Bluetooth devices, as well as from other devices operating in the ISM band like 802.11b/g and Zigbee. Finally, we show as an example how to use our model to obtain some results for the transmission of a voice stream. Copyright

CHRONO-SCHEDULING: A SIMPLIFIED DYNAMIC SCHEDULING ALGORITHM FOR TIMING PREDICTABLE PROCESSORS

We propose a simpler and latency-reduced instruction scheduler, called chrono-scheduling algorithm, which avoids large and difficult instruction wake-up in order to reduce power consumption and latencies. The key idea of this scheduler is to extract and record all possible information about the future execution of an instruction during its issue, so as not to look for this information again and again during wait stages at the reservation stations. Therefore, an instruction can be issued with the information about at what cycle its operands must be captured and when it must be executed. The first implementation is targeted to processors that have constant latencies like many embedded microcontrollers, most vector processors without data cache, etc. Its main advantages are: no tags, no renaming, and much simpler waiting stations. When compared with classical dynamic schedulers, chrono-scheduling provides approximately the same CPI but with simpler overall circuitry and presumably higher clock speed (mainly because of its simplified stations).

Tools for address-event-representation communication systems and debugging

Address-Event-Representation (AER) is a communications protocol for transferring spikes between bio-inspired chips. Such systems may consist of a hierarchical structure with several chips that transmit spikes among them in real time, while performing some processing. To develop and test AER based systems it is convenient to have a set of instruments that would allow to: generate AER streams, monitor the output produced by neural chips and modify the spike stream produced by an emitting chip to adapt it to the requirements of the receiving elements. In this paper we present a set of tools that implement these functions developed in the CAVIAR EU project.

Performance analysis of single-slave Bluetooth piconets under cochannel interference

We present an analytical model for single-slave Bluetooth piconets when the coexistence of multiple interfering devices produces collisions. Closed-form expressions for the channel throughput and the mean packet delay are obtained, including the time spent waiting on the nodes queue. The effect of propagation losses and asynchronous piconets are also discussed. The results of the analysis are validated through simulation.

A two-level dynamic chrono-scheduling algorithm

We propose a dynamic instruction scheduler that does not need any kind of wakeup logic, as all the instructions are “programmed” on issue stage to be executed in pre-calculated cycles. The scheduler is composed of two similar levels, each one composed of simple “stations”, where the timing information is recorded. The first level is aimed to the group of instructions whose timing information cannot be calculated at issue (for example, those instructions whose latency is not predictable). The second level contains simple “stations” for the instructions whose execution and write back cycle have been already calculated. The key idea of this scheduler is to extract and record all possible information about the future execution of an instruction during its issue, so as not to look for this information again and again during wait stages at the reservation stations. Another additional advantage is that time critical parts can be identified as instruction timing information is available, so high speed and frequency logic can be used only in these parts, while the rest of the scheduler can work at lower frequencies, therefore consuming much less power. The lack of wakeup and CAM (Content Addressable Memory) means that power consumption and latencies would be presumably reduced, frequency would probably be made higher, while CPI (clock Cycles Per Instruction) would remain approximately the same.