Lumistar LS-50 PCM frame configuration

[Peter K]

Hello, gang--

I have a question on IADS configuration of the Lumistar LS-50 Decom
module. We have our normal telemetry PCM frame configuration set to
use a trailing sync pattern (at the end of each minor frame). We set
this frame up via the Acra KSM Workbench and generate a Xidml file,
which we select when starting up IADS. We recently changed
configurations on receivers and turned on the shared memory feature of
the LS-50 dll. Looking at the frame dump of the card via the shared
memory feature, we noticed that it was acting as if the sync pattern
was positioned at the beginning of each minor frame (i.e. leads). We
thought that was a bit strange, but enabling debug logging on the .dll
shows that IADS is indeed configuring it for leading sync pattern, in
contrast to the Xidml. I was wondering if IADS is supposed to be
using the Xidml configuration data for setting the sync pattern
location or whether this is hard-coded in IADS to always be set to
leading.

Thanks,
-Peter

[Kathy Rodittis]

The frame sync operates "circular" in IADS meaning that you need data banded
by 2 frame syncs in order for it to be declared "good". So from a
"programming the decom" perspective it doesn't matter where you declare the
frame sync -- the end or the beginning. To to be consistent I just program
it one way across all decoms, all instrumentation files.

-Kathy

[Kathy Rodittis]

Actually even without the action of the IADS decom engine, a PCM frame sync
is a "circular" concept anyway. It's not like a CRC -- it doesn't "relate"
to either the bits that preceded or followed it. So how you program the
decom is really just a matter of taste or more to the point what the
software that uses the data is expecting. (In fact, some decoms won't even
allow you to "move" the frame sync definition.)

[Peter K]

Thanks for the information, Kathy!

[Kathy Rodittis]

My pleasure...