[Gb-ccb] CCB architecture issues/status

[Richard Lacasse]

Brian,

At the risk of muddying the waters again, let me point out that one *has* to 
assure that the 1PPS and 10 MHz are properly phased at the input to any device. 
   If the edges are nearly concident, which rarely happens, you add some cable 
to one of the lines to assure specified setup and hold times.  If the edges are 
nearly coincident then you risk metastable operation and an uncertainty of one 
clock period in synchronizing yourself to the site standard. If Martin wants to 
retime it that won't hurt anything.  However if we don't check the phase of the 
two signals when we're setting up the equipment, we've not done our homework.

Rich

Brian Mason wrote:

> hi all- I think I speak for everyone in saying I will be very glad to see
> all of the architecture issues sorted out! Notwithstanding the frustration
> involved in the process-- much of which can be ascribed to the medium of
> email, and the time-delay/ordering effects it causes-- I think a great
> deal of progress on the technical issues is being made.
> 
> The key issues seem to be
> 
> 1. Do we have to use USB 2.0 or can we use USB 1.0?
> 
> 2. How should we synchronize the FPGAs using 1PPS + 10MHz?
> 
> On the second point-- and in connection with Martin's suggestion to
> generate a 1-PPS pulse that is delayed to the opposite edge of the 10MHz
> signal-- I'd like to highlight the provision in Randy's architecture for
> timing signal conditioning (he pointed this out in an email yesterday
> afternoon).  It's not something we've needed to do for other applications,
> but if it simplifies the FPGA programming and improves reliability in this
> case we should do it.
> 
> I would like to suggest that everyone focus on these issues.  When we
> reach a consensus on them we will be able to make much more progress on
> the detailed work still ahead of us.
> 
> I'm going to be travelling next week but I suggest we plan on a telecon
> early the following week (01mar).  Meanwhile Randy & Chuck are moving
> ahead with assembling the detector circuit, and we are planning the suite
> of lab tests that will be needed for it.
> 
>  Brian
>