Reading at:
http://www.linuxcnc.org/docs/html/gcode_main.html#r1
I found mention of "global named parameters" and "Sequences like
#<named parameter> are replaced by the value of the named parameter."
Under the heading "1 G Code Reference" named parameters are not offered,
though:
>>>
A real value may be :
...
* A parameter value, #88
...
<<<
I finally found a buried reference here:
>>>
3.6 Computing values in O-words
In O-words, Parameters (section [->]), Expressions (section [->]),
Binary Operators (section [->]) and Functions (table [->]) are
particularly useful.
<<<
May I propose an entry for "1 G Code Overview" in the gcode_main.html
table of contents, linking to
http://www.linuxcnc.org/docs/html/gcode_overview.html ?
It would be a very useful asset, I think.
>From the example showing that the first assignment to a named parameter
is its declaration, I infer that a named parameter is not constrained to
be a synonym for one of the 5399 numbered parameters of the virtual
machine which EMC2 emulates. (That's a relief. :-)
It was a shock to read that the line:
#3=6 G1 x#3
causes a move of 15, if #3 had most recently been assigned that value in
a prior program line.
In the section "3.5 Don't put too many things on one line" is there
then merit in changing:
>>>
Similarly, don't use and set a parameter on the same line, even though
the semantics are well defined. (Exception: Updating a variable to a new
value, such as #1=[#1+#2])
<<<
to:
>>>
Similarly, don't set a parameter, then use it on the same line, because
assigments do not take effect until the next line. This assignment
postponement means that the following two lines have identical effect:
#3=6 G1 x#3 (Possibly smash into workpiece or fixture,)
G1 x#3 #3=6 ( if e.g. #3 holds the value 40. )
And since
#3=6 #5=[2*#3]
similarly assigns 80, not 12, to #5 in this case, it is safest to place
only one assignment on a line.
<<<
In the current text, "use and set" is actually not a problem, because
that order is not affected by assignment postponement. Thus,
"#1=[#1+#2]" is not an exception, because it doesn't attempt to utilise
the result of a prior assignment on the same line. (Not least because
there is only a single assignment. ;-)
Hopefully my beginner's brain has got that sufficiently right for the
suggestions to be useful. :-)
Regards,
Erik
--
Do not do unto others as you would they should do unto you.
Their tastes may not be the same.
-- George Bernard Shaw
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