Experimental Physics and
Industrial Control System

[email protected] (William Lupton) · Fri, 12 Apr 96 13:55:41 HST

Dear all,

  There is vxWorks global variable device support for ai, ao, longin,
longout, stringin and stringout records. The vxWorks global variable is
the same as that of the record but omitting characters up to and
including the first ":" (if any) and characters including and after the
last ";" if any. Thus record name "ppp:var;sss" corresponds to variable
"var".

  I have a project where I want to hook up to quite a lot of vxWorks
variables in some legacy software. Some of the variable names are quite
long. Other variables are structures and I would like to define new
globals which are the addresses of interesting bits of these
structures.

  I propose extending device support to make use of the INP and OUT
fields and to use an INSTIO string to hold the variable name (36
characters are available) plus to support a leading "*" character to
force an extra dereference. If the field is not INSTIO, existing
behavior will occur, so the change is upwards-compatible.

  One could also support trailing "[n]" or "+n" syntax to reference the
nth element of an array or at a byte offset of n. Is this worth it?

  An example: the string "fred" used on an ai record references the
double stored in fred; the string "*fred" references the double pointed
to by fred (cf. C "double *fred"); the string "*fred[2]" references the
third element of the double array pointed to by fred; and so on.

  Has anyone already done something similar or have any comments on the
above proposal?

  William

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System