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<== Date ==> <== Thread ==>

Subject: Re: snc/seq enhancements ... local-variable access
From: Tim Mooney <mooney@aps.anl.gov>
To: "Laznovsky, Michael" <lazmo@slac.stanford.edu>
Cc: tech-talk@aps.anl.gov
Date: Tue, 04 Apr 2006 07:30:19 -0500


Laznovsky, Michael wrote:
Greetings EPICS fans- I'm sending this email to solicit suggestions and comments for some snc/seq enhancements I'm working on, in this case support for access to local variables within sequence code.

Access is provided by show/get/put functions, and also via special PVs when a small database is added to the IOC. Progress thus far includes snc producing the required data structures and the aformentioned seq functions. For example, the following illustrates a set of declarations in a source file and the output of a series of "seqVarShow" calls:

	char         errmsg[256];
	char        *pbuf;
	char        *pbuf2;

	short        n;
	int          xyz[5][10];
	unsigned int m;
	long         foo;

	float        a;
	double       z;
.....

Get thread ID:

	epics> seqShow
	Program Name     Thread ID  Thread Name      SS Name
	zz99Control      1e7a80     zz99seq          zz99_ctrl

"seqVarShow" with no arguments displays all local variables in all state programs (or you can provide the thread id as an argument to limit output):

	epics> seqVarShow
	Program: zz99Control
	  Name                  Type            [n][n]  Address Value
	  -----------------------------------------------------------
	  errmsg                char            [256]   1e5334  "0"
	  pbuf                  char *                  1e5434  (NULL)
	  pbuf2                 char *                  1e5438  192270 -> "90 0 34 ..."
	  n                     short                   1e5448  "-77"
	  xyz                   int             [5][10] 1e5536  "3"
	  m                     unsigned int            1e544c  "1"
	  foo                   long                    1e5330  "0"
	  a                     float                   1e543c  "1.0"
	  z                     double                  1e5328  "0.1873811581904769"

"seqVarGet" with thread ID and variable name displays just that variable:

	epics> seqVarGet 1e7a80,"z"
	"0.9685835438816328"

"seqVarPut" with thread ID, variable name, and value (as string) modifies the variable:

	epics> seqVarPut 1e7a80,"m","33"
	epics> seqVarGet 1e7a80,"m"
	"33"

Things to note (all preliminary at this point):

Both reentrant and non-reentrant cases are properly handled.

Variables of type "pointer" are resolved, so that the objects pointed to are get/put, rather than the pointers themselves (unless the pointer is NULL). Maybe provide a way to alter the pointer itself?

Character arrays (strings) are displayed/entered as numeric byte sequences (could be selectable?).

Need a general way to get at arbitrary array elements. Currently only the first element is accessible.

While local variables are file-scoped (and thus shared by all state sets within a given source file) the only way I see to uniquely identify a collection of them is via a "thread ID"... "program name", "thread name", and "SS name" are all potentially subject to collisions when multiple sequences are loaded and/or invoked.

Short-term future plans include database and EDM display infrastructure to support run-time debugging of state programs, including state single-stepping and forced out-of-order transitions.

Feedback welcomed.

Single stepping would be very cool. I'm not sure what you mean by "forced out-of-order transitions", but it sounds promising.

The improvement I've heard people wish for most is syntax that would allow
them to change the next state from within a when clause.  Is this what you
mean, or is this anywhere on the list of plannedimprovements?

To be clear, I'm thinking it would be nice to be able to write something
like this:

    when (<event>) {
        if (trouble) nextState = B /* go there after when clause is done */
    } state A                      /* default if 'nextState' is not set */

I've looked at the code to see if this is even a possibility, and aside from
one thing, it does seem achievable.  The one thing is that the sequencer sets
up event flags for the next state before it even starts executing a when clause.
I don't know if this is really necessary, though.

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

References:
snc/seq enhancements ... local-variable access Laznovsky, Michael

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