A multiway switch record for the new switchable links.

[npr@jach.hawaii.edu (Nick Rees)]

I have been using R3.13.0 alpha 5 for a while now, and even had
occasion to use the switchable links. What we appear to need now is a
switch record, and probably a multipole, multiway switch record.

I have thought a bit about how this could work. Take the example of a
single pole multiway switch which can make a single input link switch
between a number of fields. Ideally it would appear on the database
diagram as connected on its input side to the multiple fields it is
switching between, and connected on the other (output) side to the
single input link. There would be a multiple choice selection mechanism
like the mbb records to select which field the input link refers to.

When the user changes the selection the record would be processed and
the link name associated with the newly selected field stuffed into the
destination records inlink.

The problem is how to get the desired effect from a database drawing,
since the definition of a link is a bit confused:

1. The output link of the switch record is connected to an link,
not a field, so this breaks a law which Capfast has considered
inviolate up to now - it resolves the case where a single wire is
connected to more than two records by saying that there must be one,
and only one, field reference. Everything else must be a link reference
and they refer to the single field. The easiest way around this (in
Capfast) is to modify the Capfast definition of the record pointed to
by the output of the switch so that the link looks like a field. Then
it will be set to zero in the database definition, but filled in by the
switch record at iocInit.

2. The record inputs are not really links, just strings, but in the
Capfast drawing they are masquerading as links so the string gets the
right linkname stuffed into it when the database is generated from the
drawing.

3. The real connection is between the selected field and the link
pointed to by the output of the switch record.

(Sorry if the description is a bit confusing, but I hope people can get
the general idea.)

Note that the same record would be able to connect a single output link
to one of a selection of input fields. However, it may be best to have
a second symbol to do this.

Anyway, has anyone thought about something along these lines? Has anyone
got anything to add?

Cheers,

Nick Rees

Joint Astronomy Centre                    Ph:       +1 (808) 961-3756
660 N. Aohoku Place                       Fax:      +1 (808) 961-6516
Hilo, HI.  96720                          Internet: npr@jach.hawaii.edu