Linux Out of the Real World
Two pairs of processes want to communicate between the orbiting experiment and the ground side support computer. The main control process in the experiment communicates with a recorder/data display/remote control program on the support computer, using several different types of data (events-log, sensor readings, and control-parameter settings going down; control and meta-control commands going up). Another pair of processes mirror directories from the payload to ground side, in order to send data that was buffered before communications were established. Images from the frame grabber are sent using this method.
In this situation, it is natural to want a packet-switching, multiplexing communication system with an interface available to many processes. Since the channel is unreliable, you want some type of validation of received data. The usual networking code is not usable, since there are no packet-drivers for the interfaces NASA presents. In the interest of simplicity and code reusability, we chose to implement a modular user-space communication system.
We wanted the communications interface presented to our communicating processes to be identical on both machines (experiment and ground side support computer). Since these two machines need to talk to different hardware and software interfaces, we abstracted the NASA interfaces from the multiplexer. Between the multiplexer and NASA sits a process that performs the packetizing and unpacketizing they want us to do (possibly fragmenting and defragmenting multiplexer packets) and relays the data. The end result is that the payload and the ground side support computer can communicate in a UDP-like fashion. Multiplexer packets sent are guaranteed to arrive intact and correct or not at all. It's a miniature networking stack in user land.
When the old DOS version of the payload flew in 1996, we rented space in SpaceHab. SpaceHab is a privately owned company that rents a large volume in the Shuttle payload bay and some services (power, communications, etc.) from NASA, and then turns around and rents smaller quantities of volume and services to experimenters. The economic relationship between the three parties (NASA, SpaceHab, experimenter) in this situation defy comprehension by the author. Anyway, SpaceHab provides a significantly more functional communications interface, called the Serial Converter Unit (SCU). Sure, it's still a 9600 bps serial line, but the SCU has (angels sing) flow control.
Sebastian Kuzminsky is an undergraduate in Computer Science and Applied Mathematics at the University at Colorado at Boulder. If space flight work were not so fun and time consuming, he would have been a graduate by now. Questions about PGBA and other Bioserve payloads are welcome. He can be reached via e-mail at email@example.com.
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
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With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide