Experimental Physics and
Industrial Control System

Dirk Zimoch <[email protected]> · Wed, 19 Aug 2009 12:42:19 +0200

Hi Dimitris,

If you want to use vxWorks (despite of the high cost and complicated licensing

model) I suggest to use a recent version. Newer boards are not supported under

older vxWorks versions. But also the opposite may be true: older boards may not

be supported under new versions.

At the moment, I try to get the MVME4100 to work. It is much cheaper than

MVME5100 or MVME6100 (which we call the VME toaster because of its high power

consumption). But the MVME4100 board needs a quite recent compiler which is only

available with vxWorks 6.7.

Generally, vxWorks 6 has some new features (e.g. real time processes) which are

not used by EPICS. vxWorks 6 still supports running applications, e.g. EPICS, in

"kernel space" (which is all you had in vxWorks 5). However, the vxWorks shell

has changed a bit and not everything that worked in vxWorks 5 startup scripts

might work in vxWork 6 startup scripts (I had difficulties sourcing other

scripts). I think I can tell more once I have the MVME4100 running.

Dirk

Dimitrios Tsifakis wrote:

Hi Andrew,

Thank you for the comprehensive response!

Your recommendations are on par with what I was thinking and what most
other people have suggested to me in private emails. The MVME series of
VME SBCs seems the logical choice given that the community has great
experience with them and the two main candidate real time OSes work well

with it.

I mentioned Linux having RTAI Linux in mind, but I don't think there are
many users of that in the EPICS world. Given the magnitude of the task
ahead of me, I am willing to "go with the flow" and select vxWorks or

RTEMS, and leave the experimentation for the future.

I noticed that most similar facilities are using vxWorks 5.5, but I
believe there is another stream, 6.7. Is there any reason to stick to
5.5 or is it irrelevant for the typical EPICS application?

cheers
Dimitris

On Mon, 2009-08-17 at 11:38 -0500, Andrew Johnson wrote:

Hi Dimitris,

Welcome to the EPICS community!

On Sunday 16 August 2009 18:22:33 Dimitrios Tsifakis wrote:

We currently have custom made systems based on older technology that
some may regard as obsolete. After reading a lot about EPICS on the net,
I have come to the conclusion that EPICS is the most reasonable choice
for upgrading our systems. As a first approach, I would like to replace
the current VME SBCs in the computer control crates with more modern
ones that can run vxWorks, RTEMS or Linux of some sort. After doing a
quick survey of the market, I have come to the conclusion that there are
many choices that will meet all the requirements, but are there any VME
SBCs that are preferred by the community for use with EPICS?

EPICS should run on almost any VME SBC that has a BSP for the appropriate OS,

but the community has experience with a limited subset of the boards

available, and if you're going to need much hand-holding you might be better

off limiting your choices to those about which we can answer questions.

Your first issue should be what RTOS you're going to use.

I don't recommend choosing Linux for VME SBCs because of the complications of

writing kernel device drivers for Linux, especially since a standard VMEbus

interface has only very recently made it into the Kernel staging area. It is

possible to mmap() VME cards into user space, but interrupt response from

such configurations leaves quite a lot to be desired. Of course if you have

experience in this area then Linux may work out fine, but don't expect much

help from us on that aspect.

That leaves a choice between vxWorks and RTEMS (unless you want to port EPICS

to another RTOS). In the past most drivers were written to use the vxWorks

APIs directly, but that is becoming much less common since we have an

OS-independent layer in EPICS and converting vxWorks drivers to use this

instead has been pretty common. As a result several recent projects have

decided to use RTEMS, which avoids having to pay annual fees to Wind River.

The advantage of vxWorks is that almost every VME SBC comes with a vxWorks

BSP, whereas RTEMS support is less common. The cost of paying OAR to write

an RTEMS BSP for your choice of hardware is not huge though, and in your

position you can probably pick boards that are already supported. VxWorks

BSPs often need tweaking slightly, and having the WRS paid support won't

preclude the need for developing some local vxWorks expertise so that aspect

of the cost is probably about even (although longer-term RTEMS may be more

flexible and work out cheaper). One advantage of picking RTEMS and a

currently-supported SBC is that you can still change your mind and switch to

vxWorks later on without having wasted any money paying for the OS!

If you're looking for a cheap work-horse SBC and don't need a top-performing

CPU, the Emerson (formerly Motorola) MVME3100 board is well-supported under

RTEMS and is used at more than one EPICS site. There are also BSPs available

for the Emerson MVME5500 and MVME6100 boards if you need more CPU power.

RTEMS also supports several older MVME boards such as the 167, 2700 and 2100

if you have existing hardware you'd like to re-use.

HTH,

- Andrew

--
Dr. Dirk Zimoch
Paul Scherrer Institut, WBGB/006
5232 Villigen PSI, Switzerland
Phone +41 56 310 5182

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System