Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Mon, 17 Aug 2009 11:38:47 -0500

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
-- 
The best FOSS code is written to be read by other humans -- Harold Welte

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System