Re: VME Bus Error handling on MVME3100 and 6100 boards

[Korhonen Timo <Timo.Korhonen@psi.ch>]

Andrew Johnson wrote:
> Kate Feng wrote:
(snip)
> > We have one application that could be optimied by the PCI  bandwidth
> > that MVME61000 offers ( 800 MHZ).
> > Also, I am still not sure about the  "MBLT" transfer of
> > the VME backplane, whih was posted at
> > http://www.aps.anl.gov/epics/tech-talk/2006/msg00888.php.
> > I assumed it was limited by the capability of the DMA controller
> > instead of the bus speed because I assume a simple test could be done
> > easily by using two MVME6100s on a VME320 crate.  Perhaps
> > Till can verify this ??
>
>
> The Tempe's DMA controllers are most likely to be limited by the speed 
> of the VMEbus when doing MBLT cycles; the maximum data transfer rate you 
> can get using MBLT is 80MB/s according to the VITA FAQ at 
> http://www.vita.com/vmefaq.html#anchor419155 whereas the PCI/X bus on 
> the MVME6100 can run faster than that.  If you have a VME320 backplane 
> and both boards are capable of 2eSST then your bottleneck might not be 
> the VMEbus, but I don't know the answer to that question.

You do not need a VME320 backplane to run 2eSST, a normal VME64x 
backplane will do (but a VME32 backplane of course not.)
Motorola claims the 6100 achieves 300 MB/s sustained. I have boards and 
crates, I try to check this out using two 6100s the next week (however, 
I do not have a 2eSST analyzer, so the results may not be that convincing.)
Anyway, the bus is not the bottleneck. A press release from Motorola says:
"On the VMEbus, the MVME6100 demonstrated 300 Megabytes per second 
memory to memory data transfers across a standard 5 row backplane using 
the 2eSST protocol. These results were reported using VMETROâs 2eSST 
VMEbus analyzer, and represent almost eight times improvement in 
previous non-2eSST VMEbus transfers."

> > Andrew Johnson wrote:
> >  > Anyone interested in MicroTCA to replace the now aging VMEbus?
> >
> > Why do you think VMEbus is aging ?  I was researching the VXS bus for
> > a short while and comapred it with  the MVME6100 solution for our
> > application.  VMEbus does not seem to be aging for me.
>
>
> The VMEbus was first announced in 1981 - that's 25 years ago, which is 
> what makes it aging as far as basic technology goes.  I'm not saying its 
> not still capable of doing the job, but the basic assumptions that the 
> bus was designed around are starting to be seriously invalidated and for 
> new facilities such as the ILC I would carefully examine alternative 
> busses such as MicroTCA.

The VMEbus has been aging for more than 20 years now...and in my 
opinion, has done pretty well. 'Old' does in my opinion not necessarily 
mean 'bad', as long as there is a path for future evolution.

We at PSI are rather looking into VXS (aka Vita 41) as the next, 
(near?)-future platform. The case for VXS for us is:

-we can smootly transition from our existing (VME64x) platform to the 
VXS. We do not have to start from (totally) scratch but can use our VME 
modules still together with VXS boards. Especially with hybrid backplanes.
-VXS would already today give us the advantages of the serial high-speed 
links over the backplane, which TCA is all about. VXS and ATCA both 
support Ethernet, Infiniband, StarFabric, RapidIO, and PCI Express on 
the backplane.
-TCA is what the name says, "TeleCom Architecture". In the end, there 
_may_ be products available that cover the spectrum that we need 
controls but I am not holding my breath... Obviously intentionally,
TCA has no backwards compatibility with anything.
-For VXS, there exists already today several very exciting products on 
the market. The downside is however the price, which tends to be rather 
high (but for multi-GSPS ADC, for example, this is to be anticipated.)

In the end, the parallel bus probably will disappear, but I would rather 
concentrate on developing the new things and continue using the existing 
ones as long as they work, rather than develop everything new from 
scratch. Which is also fine, if one can afford it.

Timo

--
Timo Korhonen  PSI (Paul Scherrer Institut, http://www.psi.ch)
               CH-5232 Villigen PSI
               tel + 41- 56 3103262  fax + 41 - 56 310 3383
e-mail:	       timo.korhonen@psi.ch