Specifications

Chapter 4
Conclusions and Recommendations
Conclusions Two Simulink S-function driver blocks for the PowerDAQ boards have been realized,
which make Hard Real-Time execution of Simulink models possible on a Linux RTAI-LXRT platform.
Together with the custom made Connector Box, a rapid control prototyping system is constructed.
Using the standard user space library functions, the PowerDAQ PD2-AO-16/16 has a maximal
sample rate of 100[kS/s] and the PowerDAQ PD2-MF-16-500/16H of 500[kS/s]. The achieved sample
rates have improved considerably for the LXRT platform in comparison to the original drivers, by using
direct kernel calls to communicate with the boards. However, the maximal sample rates of the DACS
is in general limited by the PC’s processor. As stated earlier, the same processor power is used in a 1
channel or a 16 channel configuration, so performance depends heavily on the number of channels
and the controller complexity.
Recommendations The DACS is not completely ready to be implemented into a real set-up. Unfortu-
nately, an error remained on the signals, consisting of noise, DC error and a gain error! Either there’s
a ground-loop, noise sensitive connections in the Connector Box or, most likely, the boards need to be
recalibrated. Also the missed-interrupt issue from chapter 3 page 9 still needs to be solved. This is
probably as simple as updating software. Of course for every set-up a set of channels and sample rate
have to be chosen/optimized!
Finally, when attempting to build a DACS on the Linux RTAI-LXRT platform the following should
be considered. Basic knowledge about Linux and RTAI and programming in c-code is expedient.
Advanced knowledge about these subjects is a definite pro. Be aware that the PowerDAQ boards in
this report work with I/O memory mapping while other PCI boards communicate with I/O ports.
Remember that any board will need specific drivers and for a RTAI implementation, only kernel
calls are allowed. Unfortunately these are not supplied by the manufacturer. This may be a criterium
when buying boards. An alternative can be the Comedi project [1]. Within this project, currently a
wide selection of supported boards can be found.
At the time the PowerDAQ boards were purchased, the Comedi project only gave a limited choice
of supported hardware but this has grown since the start of this project. So it is recommended to
either buy a board for which a Comedi driver is already available or write a driver yourself, according
to the conventions of the Comedi project.
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