[evla-sw-discuss] Keeping track of spectral windows at the EVLA: SDM vs. BDF

[Michael Rupen]

Hello all --

   we've gone a full round on the enumerations and on the ordering of SpW,
so here's the final decision (for now, anyhow :) --


1- On the enumeration front let's stick with what Sonja has just
   put in:

     A1C1_3BIT  A2C2_3BIT  AC_8BIT   B1D1_3BIT  B2D2_3BIT  BD_8BIT

   I believe that order is alphabetic and deterministic.
   - Note that as Barry says we will never have, e.g.,  both A1C1 and AC,
     so the relative ordering of AC and A1C1 doesn't really matter.

   There are two objections to this choice:
   * SSS uses A0C0. Since I always hated that (I can never remember whether
     3-bit starts at 1 or 0, given all the 0/1-relative confusions already
     present in the correlator) this doesn't bother me.

   * We're embedding two different types of information in one value.
     A1C1 etc. tell you the basebands; 3BIT and 8BIT tell you what the
     samplers produce from those basebands.  This is OK from the EVLA
     perspective (it's how the hardware is set up), but annoying in the
     context of the SDM.  For now I think that's OK.


2- As to the ordering of swIndex, let's adopt the revisions suggested
   by Sonja & David:

   1- swIndex is ordered according to the lower edge of the lowest
     frequency channel in each SpW (lower frequencies come first)

   2- for remaining matches, give the lower swIndex to the SpW with
     the narrower total bandwidth

   3- for remaining matches, give the lower swIndex to the SpW with
     more (hence narrower) channels

   4- for remaining (exact) matches, the lower VCI sbid (subband ID)
     gets the lower swIndex

   ***This ordering should be based on the _output_ of the CBE, _after_
     any CBE processing such as smoothing-and-decimation, subselection of a
     group of channels, etc.***  The distinction is not relevant yet but
     will be in the future (months from now).


Let me know if you have strong objections, but I think it's time to
close these issues off.

   Cheers,

               Michael