[Gb-ccb] suggested changes to ccb library

[Melinda Mello]

Brian Mason wrote:

> Martin Shepherd writes:
>  >
>  >
>  > On Mon, 11 Aug 2003, Brian Mason wrote:
>  > >  a) reordered error messages: not a *requirement*, just something
>  > >  that would be really nice. This will help us "throw out" (actually,
>  > >  send to a log file, rather than our message system) messages of the
>  > >  sort that we don't normally have in the message system.
>  >
>  > An alternative that I would prefer would be to include another
>  > enumerated argument with the log messages, specifying their type. I
>  > would imagine that this would be easier at your end too. Would this be
>  > acceptible?
>
> Melinda can comment here...
>

Adding an enumeration to the argument list is fine with me.

>
>  >
>  > >  b) a simulation mode of the actual ccb server; the goal here is
>  > >  to have as much of the code as reasonably feasible be identical
>  > >  between the simulation and the real thing. Again not an absolute
>  > >  requirement, but something which we believe will pay off.
>  >
>  > Agreed.
>
> Great
>
>  >
>  > >  c) possibly, we would like to use the "scan control bit" which is
>  > >  in the device interface, to control scans. We currently have
>  > >  proposed a somewhat awkward mechanism in which the manager secretly
>  > >  starts a scan just before a real scan (outlined in draft form in
>  > >  the use cases Melinda and I wrote some time ago). Currently i believe this
>  > >  bit is not accessible via the server, ie, the server interface hides
>  > >  this bit and manipulates it itself (possibly for very good reasons:
>  > >  we don't know, and would like to discuss it).
>  >
>  > This bit needs to be toggled at precise instants that can only be
>  > achieved by real-time interrupt handlers, so it would make no sense
>  > for the server to have access to it. This is also only one of many
>  > control bits, all of which need to be toggled with real-time
>  > precision.
>
> I see...
>

It's not at all clear from the "The hardware interfaces of the CCB" -1/22 document,
that there are any timing constraints for the start scan bit.
I agree with Brian, that we should let it lie.
Eventually, the documentation should be updated to reflect reality.


>
>  >
>  > Could you tell me what the problem is that you are trying to work
>  > around? Since new configuration information doesn't have any effect
>  > until a new scan is started, I can't imagine a situation where one
>  > might need a dummy intra-scan.
>
> The issue is that a new scan can't start until the current integration
> is done. Potentially this is a longer delay than we want.  I believe
> we determined this by working through one of your (or Yamasaki's?) old
> state machine diagrams and are not sure if it's still true given
> revisions to the design.
>
> In any case we *do* have a work around and it sounds like we should
> let this one lie.
>
>  >
>  > Beware that the internals of the device driver are liable to change
>  > significantly, now that I am doing the hardware. The server interface
>  > that I have provided to you is supposed to insulate you from those
>  > changes, so if something in the server interface can't accomodate your
>  > requirements, then I need to fix it at that level, without explicit
>  > reference to the specific device-driver/hardware implementation.
>  > Thinking about, and specifying server changes in terms of
>  > hardware-level implementation details, such as the start-scan bit,
>  > isn't a good idea.
>
> Ok.
>
> One thing which would be useful is to check my old draft "use case"
> document against the current server interface. I'm not sure how much
> the interface has changed.
>
>  Brian
>
>  >
>  > Martin
>
> --
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> Brian Mason                           | office: +1(304)456-2338
> Assistant Scientist                   | fax:    +1(304)456-2229
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> bmason at gb.nrao.edu                    |         Green Bank, WV 24944
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