Mark Crane

Review of the Real-Time 99 conference in Santa Fe NM June 1999

The first day of the conference was split into a number of different tracts. I chose the hardware tract which included a half day tutorial on VME / Compact PCI followed by an afternoon discussing real-time Linux.

In the first session a number of things stood out. The biggest issue is the move from parallel backplanes to serial buses for interconnect of computing elements. Intel's Next Generation I/O, or NGIO, poses the largest threat to VME and compact PCI. The issue with parallel buses is that the individual channels are skewed in time as they cross the backplane. With a serial bus this is not an issue since everything it self clocked. The Web site for NGIO is WWW.NGIOforum.org. Another major issue is that the costs for VME and compact PCI are based upon the packaging and the interconnect, not necessarily the computing components on the boards. This is why your commodity devices do not always show a reduction in cost. The biggest advantage to using Compact PCI is the PCI software, which is written for commodity devices, is reusable in these commodity products. The issue with VME is that few users write PC based drivers for control systems on VME.

The second half of the first day was a focus on real-time Linux or RT Linux. In this is free real-time scheduling software which allows you to run real-time tasks, with your own scheduler, and then run the normal Linux operating system on top of it. This makes Linux run just as the idle task in the scheduler. It solves the problem where you have very simple real-time needs and need to have the upper layers support such as networking and screen I/O, and be able to use one operating system on a commodity device. Designs using this model use strict real-time code at the lowest level and any non-real-time needs use normal Linux. An interesting point is that you can insert your own scheduler algorithm in place of what's shipped with the code. This would allow you to do round robin or priority scheduling to suit your needs. The Web site for this is linux-rep.fnal.gov/realtime.

The next four days of this conference were split up into differing parts of real-time data acquisition systems. The focus here was on large-scale experiments with a few small experiments in for good measure. All projects were physics related experiments, most of them acquiring data from the events and processing this data in somewhat real-time terms. Here I have listed general observations for these four days. I have detailed notes on each of the presentations for future reference.