Experimental Physics and
Industrial Control System

<[email protected]> · Fri, 7 Jun 2013 08:01:48 +0000

From: [email protected] [mailto:tech-talk-
> We would like to set a SCAN field on several lower level BO records, at
> the same time, and the value of these SCAN fields should reflect the
> value of the single higher level record SCAN field.
> 
> For the control of these lower level SCAN fields another, higher level
> record, would be used. If a user wishes to set individual lower level
> record SCAN fields, she is allowed. OTOH, when changing the SCAN of the
> higher level record, ALL lower lever BO records would get their SCAN
> field set too.
> 
> Is it possible to get this done without using a sequencer?

I suggest an alternative architecture:

1. Have a single controlling record with controllable SCAN.

2. Set all your low level records to SCAN='Passive'

3. Use a chain of fanout records to force processing of the low level records

4. Use the FLNK of the controlling record to trigger the fanout.

Using the Python based EPICS database builder I would write this construction as:

	low_level_pvs = [records.bo('BO%d' %n) for n in range(16)]
	control = records.bo('SCAN', SCAN = '.1 seconds',
	    FLNK = create_fanout('FAN', *low_level_pvs))

The corresponding database would look something like this:

	record(bo, "$(device):BO0") { }
	...
	record(bo, "$(device):SCAN")
	{
	    field(SCAN, ".1 seconds")
	    field(FLNK, "$(device):FAN")
	}
	record(fanout, "$(device):FAN")
	{
	    field(SELM, "All")
	    field(LNK1, "$(device):BO0 PP")
	    ...
	    field(LNK6, "$(device):FAN1")
	}
	record(fanout, "$(device):FAN1")
	{
	    field(SELM, "All")
	    field(LNK1, "$(device):BO6 PP")
	    ...
	}

(I think you see why I'd write this in Python!)

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System