Re: Need up-to-date documentation for SCAN record

[Tim Mooney <mooney@aps.anl.gov>]

re...,

> > Actually, most of the changes made in '95/'96 were in implementation of
> > existing features, and the Record Reference Manual still serves pretty
> > well with some exceptions: positioner readback arrays (PnRA), positioner 
> > after-scan mode (PASM), positioner absolute/relative (PnAR), and some new
> > options for the CMND field are not in the Record Reference Manual.  For
> > these fields, the best available doc is still in the source code.
> 
> best == only

Whatever.

> Finding all the places and ways that Relative Mode (which should be a simple
> concept) affects operation from reading the code is non-trivial.

True.  In every case, relative mode takes the value that would have
been written directly to a positioner and adds to it the pre-scan
position.  That's all it does.

When you're looking through the code for numbered fields, such as x1yz,
and you don't find them, try x_yz.  Most numbered fields are regarded
internally as elements of arrays.  I'm telling you this because the
likelihood that you'll find all the information you want in external
documentation is negligible.  Code development frequently outruns
documentation development.

> What does PREVIEW (CMND = 2) do ?

It does a dry run through the scan to check that no positioner will be
directed to violate its limits.  (There remains a defect in the
evaluation of limits, by the way.  They are read only once, when the
link is first made to a positioner.  I haven't had time to address this,
but it's on the list.)

> How to know the distinctions between
> 
> 	scanPASM_Start_Pos (REC_SCAN_AS_ST)
> and
> 	scanPASM_Prior_Pos (REC_SCAN_AS_BS)

These values tell the scan record what to do with positioners after the
scan is finished.  scanPASM_Start_Pos tells the record to move
positioners to the location of the first data point; scanPASM_Prior_Pos
tells the record to move positioners to the locations they were in
before the scan ever started.

> as the PnPP fields are not documented ?

These fields are intended for the private use of the scan record.  They
save positioner values from before the scan.

> Also undocumented :
> 
>        Before/After Scan PVs/CMDs (looks very useful)

Simply a link and a value.  Before the scan starts, BSCD gets written
to the PV whose name is stored in BSPV, and the record waits for
completion before moving to the next phase of the scan.  When the scan
is finished, ASCD gets written to the PV whose name is stored in ASPV.

>        DPT

Can't find this field.

>        PnPP

positioner value prior to beginning of scan

>        PnCV

positioner current value

>        DnNE

number of elements in detector array.  Array valued detectors are not
supported until version 5.01 of the sscan record (renamed after version
4.0 because I couldn't figure out how to make put_callback behavior
backward compatible with the scan record).  This is still in beta
testing.

Thanks, by the way, for compiling this list of undocumented fields.
It's both a help and an incentive.

> ----
> Brian McAllister                 Application Programmer/Beam Physicist
> mcallister@mit.edu                        MIT-Bates Linear Accelerator

Tim Mooney (mooney@aps.anl.gov) (630)252-5417
Beamline Controls & Data Acquisition Group
Advanced Photon Source, Argonne National Lab