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<== Date ==> | <== Thread ==> |
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Subject: | RE: compact PCI versus VME |
From: | "Jeff Hill" <[email protected]> |
To: | "'Lawrence T. Hoff'" <[email protected]>, "'Dalesio, Leo'" <[email protected]> |
Cc: | Eric Bjorklund <[email protected]>, [email protected] |
Date: | Tue, 26 Jan 2010 09:04:38 -0700 |
FWIW: At LANSCE we are looking
at NI’s cRIO for slow controls – this eliminates
the two parallel universes problem when interfacing EPICS to ladder logic based
PLCs. That of course makes sense only when you need a slow controls IOC, and you
don’t need the traditional safety role of a PLC (the cRIO’s
FPGA might even be used for equipment protection if proper change tracking verification
procedures are in place). The cRIO _is_ proprietary,
but also very flexible in terms of hard synchronization and parallel processing
because of the programmable FPGA on the backplane. At KEK they have the EPICS
IOC embedded in the Yokagowa PLC. It’s a similar idea, w/o the flexibility
of the FPGA on the backplane, but with the wiring benefits and longevity of PLC
hardware. The cRIO is also being looked at here for
BPMs and Wire Scanners. It’s unfortunate, from my perspective, that there
isn’t an open standard equivalent of cRIO
(correct me if I am wrong on that conclusion). For LANSCE LLRF they need
the real-estate provided by 6u boards, and for DAQ the bandwidth between the
FPGA and the analog modules isn’t appearing to be sufficient in cRIO. So for those systems we need either cPCI, VME, or uTCA. If we have a
centralized CPU then the bandwidth in cPCI Express, VME/VXS,
or uTCA for DAQ interconnects looks attractive. Another
option which we are looking at is to just run EPICS embedded on every one of
the (Ethernet directly connected) DAQ/LLRF modules thereby eliminating the
system interconnect as a bottleneck/complexity between the DAQ/FPGA hardware
and switched Ethernet. I suspect that the need for
a special ASIC to drive the higher voltages on the VME bus is one reason why
VME seems to cost more compared to cPCI which uses
lower backplane voltages. Another reason is of course economics of scale with PC
commodity chips. That particular price advantage could vanish as PCs move off
to wherever PCs move off to, but cPCI Express appears
to track that at least for awhile. The VME/VXS functional equivalents does not
appear to be quite as far along at this time compared to cPCI
Express. I am not seeing high signal density digitizer modules that conform to the
new VME switched serial standards. I am also unaware of any VME digitizers with
an embedded general purpose Ethernet connected processor on which we can directly
embed EPICS (that option does exist in cPCI). I am very interested in any suggestions
you might have BTW. Jeff
Message
content: TSPA From: Lawrence T. Hoff [mailto:[email protected]] I see an interesting theme in
this discussion - although I am sensitized by "internal" (RHIC) discussions
we had last week.... My thoughts this morning
(for what they are worth): These days, accelerator controls
seems to include two somewhat distinct disciplines:
1) "slow controls" - digital I/O, PLC-based logic, analog I/O at the ~10Hz or slower level,
vacuum, cryo, etc.
2) Data acquisition (DAQ) systems - including global orbit correction at the many KHz level,
turn-by-turn (and even bunch-by-bunch) beam diagnostics, LLRF, etc.
The former benefits from low "per-channel" costs, modularity, scalability, long lifetime,
etc. This has been reasonably served by VME historically. It is hard to
imagine, e.g. that uTCA would be well suited for such applications. DAQ
systems requires high bandwidth, large memory, powerful processors (or
FPGAs). To
date, we (RHIC) have "made do" with VME for *both* roles - occasionally bumping into VME
limitations for the most demanding applications, but for the most
part happy to have a one-size (mostly) fits all solution.
Recently, we debated investigating non-VME crate solutions (e.g. uTCA) - Still trying to maintain a
one-size-fits all solution. Our concern was whether we could find a platform with
the bandwidth needed for even more demanding DAQ systems moving forward, but
still retain the low per-channel costs for "slow controls"
(hence my interest in Jeff's observation about low-cost CompactPCI modules).
One thought was to investigate whether (PMC?) daughter-cards could be used for "slow controls"
(to control per-channel costs) - only using the (expensive, switched serial) backplane for
high-bandwidth applications.
Another thought - what Bob seems to be suggesting - is to give up on the one-size-fits-all solution
- instead select platforms optimized for DAQ applications and other
platforms optimized for "slow control" applications.
RHIC is de-facto heading in that direction - continuing to use VME32 (as well as NI Compact
RIO and inexpensive PLCs) for "slow controls", and relying on a newly
developed crate-less solution for DAQ applications - based on a XILINX FPGA with PPC
hard core, and 6 XMC daughter card sites for modularity.
It isn't obvious to me that CompactPCI is significantly better (or worse) than VME for
"slow controls" - but I am still interested to hear other's experience. I
suspect that Compact PCI bandwidth is *not* so significantly
better than VME that it would satisfy our demanding DAQ needs moving
forward (but I am willing to be corrected). I strongly suspect that our DAQ
needs can only be met by a switch-serial backplane standard *or*
a crate-less solution such as our FPGA-based system - but again, I'm all
ears and ready and willing to be corrected. -- Larry From: Dalesio, Leo
[mailto:[email protected]] Sent to Eric regarding cPCI for timing:
When we want a small IOC, the Moxa unit has
an arm processor and is configured to integrate serial and Ethernet
instruments. =======================================
Bob -----Original Message----- I
have absolutely NO experience with CompactPCI. Having
said that, we do recognize that VME has I
am also interested in switched-serial-only -- Larry > -----Original Message----- |