[Difx-users] Native Mark5 and Mark6 update

[Walter Brisken]

Hi DiFX users,

NRAO is in the process of retiring its last Mark5 units.  Without these 
available, performing maintenance on the native Mark5 playback 
capabilities within DiFX code will be near impossible.

At the same time, I've been improving support for VDIF playback for 
file and native Mark6 playback.  Working code is in a new branch of 
mpifxcorr: https://svn.atnf.csiro.au/difx/mpifxcorr/branches/fixvmux . 
The updates include more flexible use of the "vdif multiplexer" which is 
used to bundle together all of the VDIF threads into a single internal 
VDIF thread which can be handled downstream within mpifxcorr.  The code 
changes have interfered with support for multi-threaded VDIF playback from 
Mark5 units, so it is likely that this specific kind of Mark5 playback 
will be disabled in the next major DiFX release.

If anyone is interested in testing the new code, you can check out the 
development (or "trunk") DiFX code as you normally would and then replace 
the checked-out mpifxcorr with the code at the branch above.  I'd be 
interested in any feedback.  In the current version, the maximum "thread 
skew" (separation in bytes between any to frames A and B, where A occurs 
eariler in the file than B and where B has a timestamp that is less than 
or equal to that of A) that is likely to yield good weights is 
approximately the size of the "Baseband read size (MB)" (as reported by 
difxcalculator), which tends to be about 20 MB using default parameters 
for wide-band observing modes.  These can be tweaked in the .v2d file with 
minReadSize and maxReadSize.

There hasn't been recent discussion of the next major DiFX release (likely 
called 2.7 or 3.0), but I expect to merge these fixes into trunk before 
the next version gets created.  I expect there will be another minor 
release of the 2.6 series before that in the not too distant future.

 	-Walter

-------------------------
Walter Brisken
NRAO
Deputy Assistant Director for VLBA Development
(575)-835-7133 (office)
(505)-234-5912 (cell)