[evlatests] phase flippiing is not in the correlator

[mluce at nrao.edu]

> The correlator is exonerated, but we are left with two mysteries.
> 1.  What is the L302 doing?  2.  Why is it doing anything?  We
> exepect it to do nothing when commanded to the frequency that it
> is already set to.

The L302 does not currently ignore commands for the same frequency.  If a
command is sent to the synthesizer for the frequency which is already
tuned, the normal DDS command sequence takes place.

In summary, the L302 firmware caches the commanded frequency, phase, and
ramp;  these values are then loaded to the DDS registers during either the
sequenced 19.2Hz period or immediately if no sequencing is specified.  The
firmare then waits until the next 19.2Hz edge, pulses the DDS IOUPDATE,
and the contents of the DDS registers get clocked into the active state
register of the DDS. This is the point when the new command takes actually
takes effect.

Matt