CCD-world: Optical Link in CCD Controller

[DE KAT Jean DAPNIA]

The following was posted to CCD-world:

Hello everybody,

as discussed in the ESO WorkShop, I find that will be great to present in
this forum some solutions and not only questions. (Maybe this would be more
efficient than some WorkShop roundtables ...)

Then I start with a common problem for all CCD controllers developpers i.e.
the optical link to evacuate the CCDs data.

I have recensed in the last 2 years the available optical links in the
market because I didn't want to develop a new one for MegaCam (for time to
develop and maintenance reasons).

I needed a performant link (100MB/s), easy to implement in my custom CCD
controller, without any high level software driver (as in FiberChannel,
gigabitEthernet, ...) and directly pluggable into commercial VME boards.

I found only 2 links like that. One from Systran is called the Simplex Link,
has a PMC form factor at both side and implement a FPDP->Fiber->FPDP
protocol. (FPDP = simple parallel communication protocol).
Unfortunately, this products seems virtual since it exists only on the web
for many months ...

The other is the SLink that I finally adopted. We plan to plug it into a
Motorola PPC board (VME board with PCI as internal bus).

Here is a description of SLink:

- SLink was developed at CERN (Particle Physics in Geneve). When we need
some optical links for our controllers, they need thousand of links for some
experiments...
- SLink won't vanish in few years; it is now sold by private companies and
the CERN experiments will need it for at least the next 10-20 years.
- SLink is not a common standard. Only the mechanics, the connector and the
protocol on this connector is defined. That allows users to benefit from
future laser/fiber/coding... technologies by just unplug the old link and
plug a new one.
- SLink allows transfers on fiber at rates > 100MB/s in one direction. There
is a second fiber but is used to secure dialog between emitter/receiver. It
can however be used but at a lower transfer rate. That doesn't matter in
most of our controllers where we have to download few commands to the
controller and upload large CCD data (except for those who believe in remote
CCD sequencing ...).
- On the controller side, SLink is seen as a synchronous 32 bits Fifo. That
is to say that the controller developer has just to implement somewhere the
SLink connector, to reserve the space for a SLink daugther board (PMC form
factor) and to interface its system to a 32 bits Fifo.
- On the other side of the fiber, we have to plug a same SLink board on a
adaptator. Adaptator for PMC, PCI, VME exist. A more compact board with a
SLink board merged with an PMC adaptator exists too.
- Various software drivers are already developped (except mine ... : we have
had to develop our driver because it didn't exist yet (PMC, VxWorks).

To summarize, SLink is easy to implement, performant, and there is nothing
to develop in VME crate. 
The only drawback I found, is that you can't use it to send a reliable reset
to your controller. You need another channel just for that.
Note too that, in most of cases, the SLink will not be the speed limit of
the whole system. In my system for example, the PPC board is the 1st limit
with 89MB/s on PCI bus.

I think that SLink could be a good solution for most of us.

For more info, you can see the WebSites:
http://www.cern.ch/hsi/s-link/
http://www.systran.com/fibrextreme.htm

But maybe someone has another solution ?

Another question:
Is anybody happy with remote CCD sequencing (sequencer at the other end of
fiber) ? What are the performances in term of sequencing speed,
synchronisation, power dissipation ?

jdK



******************************************
jean de Kat - Electronics Engineer
CEA-Saclay, Dapnia/Sei
91191 Gif-sur-Yvette, FRANCE
Tel: 33 1 69 08 85 05   or  33 1 69 08 62 81
Fax: 33 1 69 08 31 47
Email: jean.de-kat at cea.fr
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