Tag Archives: Soft Real-time

A ROS module that improves real-time aspects of network communication among distributed ROS machines, and a nice analysis of wireless network characteristics and limitations

December 10, 2018 16:22 ,

Danilo Tardioli, Ramviyas Parasuraman, Petter Ögren, Pound: A multi-master ROS node for reducing delay and jitter in wireless multi-robot networks, Robotics and Autonomous Systems, Volume 111, 2019, Pages 73-87, DOI: 10.1016/j.robot.2018.10.009.

The Robot Operating System (ROS) is a popular and widely used software framework for building robotics systems. With the growth of its popularity, it has started to be used in multi-robot systems as well. However, the TCP connections that the platform relies on for connecting the so-called ROS nodes presents several issues regarding limited-bandwidth, delays, and jitter, when used in wireless multi-hop networks. In this paper, we present a thorough analysis of the problem and propose a new ROS node called Pound to improve the wireless communication performance by reducing delay and jitter in data exchanges, especially in multi-hop networks. Pound allows the use of multiple ROS masters (roscores), features data compression, and importantly, introduces a priority scheme that allows favoring more important flows over less important ones. We compare Pound to the state-of-the-art solutions through extensive experiments and show that it performs equally well, or better in all the test cases, including a control-over-network example.

Posted in: Robotic software , Tagged: , , ,

Soft-real time scheduling in distributed systems based on accrued utility of distributable threads, including situations of node failures

May 20, 2015 09:19 ,

Ravindran B., Anderson J. S., Jensen E. D., On Distributed Real-Time Scheduling in Networked Embedded Systems in the Presence of Crash Failures, Lecture Notes in Computer Science, vol. 4761, pp. 67-81, DOI: 10.1007/978-3-540-75664-4_8.

We consider the problem of scheduling distributable real-time threads in networkedembedded systems that operate under run-time uncertainties including those on thread execution times, thread arrivals, and node failure occurrences. We present a distributed scheduling algorithm called CUA. We show that CUA satisfies thread time constraints in the presence of crash failures, is early-deciding, has an efficient message complexity of O(f n) (where f is the number of crashes that actually occur and n is the number of nodes), and is time-optimal with a time lower bound of O(D + f d + nk) (where D is the message delay upper bound, d is the failure detection bound, and k is the maximum number of threads). In crash-free runs, the algorithm constructs schedules within O(D + nk), and yields optimal total utility if nodes are also not overloaded. The algorithm is also “best-effort” in that a high importance thread that may arrive at any time has a very high likelihood for feasible completion (in contrast to classical admission control algorithms which favor feasible completion of admitted threads over admitting new ones, irrespective of thread importance).

Posted in: Real-Time Systems , Tagged: , ,