o-code.rst

O Codes
=======

O-codes provide for flow control in NC programs. Each block has an associated number, which is the
number used after O. Care must be taken to properly match the O-numbers. O codes use the letter ``O``
not the number zero as the first character in the number like O100 or o100.

Numbering
---------

Numbered O codes must have a unique number for each subroutine,

Numbering Example

::

   (the start of o100)
   o100 sub
   (notice that the if-endif block uses a different number)
     (the start of o110)
     o110 if [#2 GT 5]
       (some code here)
     (the end of o110)
     o110 endif
     (some more code here)
   (the end of o100)
   o100 endsub

Comments
--------

Comments on the same line as the O word should not be used as the behavior can change in the future.

The behavior is undefined if:

* The same number is used for more than one block
* Other words are used on a line with an O- word
* Comments are used on a line with an O-word

[TABLE]

Subroutines
-----------

Subroutines starts at ``Onnn sub`` and ends at ``Onnn endsub``. The lines between ``Onnn sub`` and ``Onnn
endsub`` are not executed until the subroutine is called with ``Onnn call``. Each subroutine must use a
unique number.

Subroutine Example

::

   o100 sub
     G53 G0 X0 Y0 Z0 (rapid move to machine home)
   o100 endsub

   (the subroutine is called)
   o100 call
   M2

See `G53 <#gcode:g53>`__ & `G0 <#gcode:g0>`__ & `M2 <#mcode:m2-m30>`__ sections for more
information.

O- Return

Inside a subroutine, ``O- return`` can be executed. This immediately returns to the calling code, just
as though ``O- endsub`` was encountered.

O- Return Example

::

   o100 sub
     (test if parameter #2 is greater than 5)
     o110 if [#2 GT 5]
       (return to top of subroutine if test is true)
       o100 return
     o110 endif
       (this only gets executed if parameter #2 is not greater than 5)
       (DEBUG, parameter 1 is [#1])
   o100 endsub

See the `Binary Operators <#gcode:binary-operators>`__ & `Parameters <#gcode:parameters>`__ sections
for more information.

O- Call

``O- Call`` takes up to 30 optional arguments, which are passed to the subroutine as ``#1``, ``#2`` , …​,
#N. Parameters from #N+1 to #30 have the same value as in the calling context. On return from the
subroutine, the values of parameters #1 through #30 (regardless of the number of arguments) will be
restored to the values they had before the call.  Parameters #1 - #30 are local to the subroutine.

Because ``1 2 3`` is parsed as the number 123, the parameters must be enclosed in square brackets. The
following calls a subroutine with 3 arguments:

O- Call Example

::

   o100 sub
     (test if parameter #2 is greater than 5)
     o110 if [#2 GT 5]
       (return to top of subroutine if test is true)
       o100 return
     o110 endif
       (this only gets executed if parameter #2 is not greater than 5)
       (DEBUG, parameter 1 is [#1])
   o100 endsub

   o100 call [1] [2]

Subroutine bodies may not be nested. They may only be called after they are defined. They may be
called from other functions, and may call themselves recursively if it makes sense to do so. The
maximum subroutine nesting level is 10.

Subroutines do not have ``return values``, but they may change the value of parameters above #30 and
those changes will be visible to the calling code. Subroutines may also change the value of global
named parameters.

Fanuc-Style Numbered Programs
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Numbered programs (both main and subprograms), the ``M98`` call and ``M99`` return M-codes, and their
respective semantic differences are an alternative to the rs274ngc subroutines described above,
provided for compatibility with Fanuc and other machine controllers.

Numbered programs are enabled by default, and may be disabled by placing ``DISABLE_FANUC_STYLE_SUB =
1`` in the ``[RS274NGC]`` section of the ``.ini`` file.

Numbered Subprogram Simple Example

.. code:: highlight

   o1 (Example 1)    ; Main program 1, "Example 1"
   M98 P100          ; Call subprogram 100
   M30               ; End main program

   o100              ; Beginning of subprogram 100
     G53 G0 X0 Y0 Z0 ; Rapid move to machine home
   M99               ; Return from subprogram 100

``o1 (Title)``

The optional main program beginning block gives the main program the number ``1``. Some controllers
treat an optional following parenthesized comment as a program title, ``Example 1`` in this example,
but this has no special meaning in the rs274ngc interpreter.

``M98 P- <L->``

Call a numbered subprogram. The block ``M98 P100`` is analogous to the traditional ``o100 call``
syntax, but may only be used to call a following numbered subprogram defined with ``o100``\ …​\
``M99``. An optional ``L``-word specifies a loop count.

``M30``

The main program must be terminated with ``M02`` or ``M30`` (or ``M99``; see below).

``O-`` subprogram definition start

Marks the start of a numbered subprogram definition. The block ``O100`` is similar to ``o100 sub``,
except that it must be placed later in the file than the ``M98 P100`` calling block.

``M99`` return from numbered subroutine

The block ``M99`` is analogous to the traditional ``o100 endsub`` syntax, but may only terminate a
numbered program (``o100`` in this example), and may not terminate a subroutine beginning with the
``o100 sub`` syntax.

The ``M98`` subprogram call differs from rs274ngc ``O call`` in the following ways:

* The numbered subprogram must follow the ``M98`` call in the program file. The interpreter will
  throw an error if the subprogram precedes the call block.

* Parameters ``#1``, ``#2``, …​, ``#30`` are global and accessible in numbered subprograms, similar
  to higher-numbered parameters in traditional style calls. Modifications to these parameters within
  a subprogram are global modifications, and will be persist after subprogram return.

* ``M98`` subprogram calls have no return value.

* ``M98`` subprogram call blocks may contain an optional L-word specifying a loop repeat
   count. Without the L-word, the subprogram will execute once only (equivalent to ``M98 L1``). An
   ``M98 L0`` block will not execute the subprogram.

In rare cases, the ``M99`` M-code may be used to terminate the main program, where it indicates an
``endless program``. When the interpreter reaches an ``M99`` in the main program, it will skip back to
the beginning of the file and resume execution at the first line. An example use of an endless
program is in a machine warm-up cycle; a block delete program end ``/M30`` block might be used to
stop the cycle at a tidy point when the operator is ready.

Numbered Subprogram Full Example

.. code:: highlight

   O1                             ; Main program 1
     #1 = 0
     (PRINT,X MAIN BEGIN:  1=#1)
     M98 P100 L5                  ; Call subprogram 100
     (PRINT,X MAIN END:  1=#1)
   M30                            ; End main program

   O100                           ; Subprogram 100
     #1 = [#1 + 1]
     M98 P200 L5                  ; Call subprogram 200
     (PRINT,>> O100:  #1)
   M99                            ; Return from Subprogram 100

   O200                           ; Subprogram 200
     #1 = [#1 + 0.01]
     (PRINT,>>>> O200:  #1)
   M99                            ; Return from Subprogram 200

In this example, parameter ``#1`` is initialized to ``0``. Subprogram ``O100`` is called five times
in a loop. Nested within each call to ``O100``, subprogram ``O200`` is called five times in a loop,
for 25 times total.

Note that parameter ``#1`` is global. At the end of the main program, after updates within ``O100``
and ``O200``, its value will equal ``5.25``.

Looping
-------

The ``while loop`` has two structures: ``while/endwhile``, and ``do/while``.  In each case, the loop is
exited when the ``while`` condition evaluates to false. The difference is when the test condition is
done. The ``do/while`` loop runs the code in the loop then checks the test condition. The
``while/endwhile`` loop does the test first.

While Endwhile Example

::

   (draw a sawtooth shape)
   G0 X1 Y0 (move to start position)
   #1 = 0 (assign parameter #1 the value of 0)
   F25 (set a feed rate)
   o101 while [#1 LT 10]
     G1 X0
     G1 Y[#1/10] X1
     #1 = [#1+1] (increment the test counter)
   o101 endwhile
   M2 (end program)

Do While Example

::

   #1 = 0 (assign parameter #1 the value of 0)
   o100 do
     (debug, parameter 1 = #1)
     o110 if [#1 EQ 2]
       #1 = 3 (assign the value of 3 to parameter #1)
       (msg, #1 has been assigned the value of 3)
       o100 continue (skip to start of loop)
     o110 endif
     (some code here)
     #1 = [#1 + 1] (increment the test counter)
   o100 while [#1 LT 3]
   (msg, Loop Done!)
   M2

Inside a while loop, ``O- break`` immediately exits the loop, and ``O- continue`` immediately skips to
the next evaluation of the ``while`` condition. If it is still true, the loop begins again at the
top. If it is false, it exits the loop.

Conditional
-----------

The ``if`` conditional consists of a group of statements with the same ``o`` number that start with ``if``
and end with ``endif``. Optional ``elseif`` and ``else`` conditions may be between the starting ``if`` and
the ending ``endif``.

If the ``if`` conditional evaluates to true then the group of statements following the ``if`` up to the
next conditional line are executed.

If the ``if`` conditional evaluates to false then the ``elseif`` conditions are evaluated in order until
one evaluates to true. If the ``elseif`` condition is true then the statements following the ``elseif``
up to the next conditional line are executed. If none of the ``if`` or ``elseif`` conditions evaluate to
true then the statements following the ``else`` are executed. When a condition is evaluated to true no
more conditions are evaluated in the group.

If Endif Example

::

   (if parameter #31 is equal to 3 set S2000)
   o101 if [#31 EQ 3]
     S2000
   o101 endif

If ElseIf Else EndIf Example

::

   (if parameter #2 is greater than 5 set F100)
   o102 if [#2 GT 5]
     F100
   o102 elseif [#2 LT 2]
   (else if parameter #2 is less than 2 set F200)
     F200
   (else if parameter #2 is 2 through 5 set F150)
   o102 else
     F150
   o102 endif

Several conditons may be tested for by ``elseif`` statements until the ``else`` path is finally executed
if all preceding conditons are false:

If Elseif Else Endif Example

::

   (if parameter #2 is greater than 5 set F100)
   O102 if [#2 GT 5]
     F100
   (else if parameter #2 less than 2 set F200)
   O102 elseif [#2 LT 2]
     F20
   (parameter #2 is between 2 and 5)
   O102 else
     F200
   O102 endif

Repeat
------

The ``repeat`` will execute the statements inside of the repeat/endrepeat the specified number of
times. The example shows how you might mill a diagonal series of shapes starting at the present
position.

Repeat Example

::

   (Mill 5 diagonal shapes)
   G91 (Incremental mode)
   o103 repeat [5]
   ... (insert milling code here)
   G0 X1 Y1 (diagonal move to next position)
   o103 endrepeat
   G90 (Absolute mode)

Indirection
-----------

The O-number may be given by a parameter and/or calculation.

Indirection Example

::

   o[#101+2] call

Computing values in O-words

For more information on computing values see the following sections

* `Parameters <#gcode:parameters>`__
* `Expressions <#gcode:expressions>`__
* `Binary Operators <#gcode:binary-operators>`__
* `Functions <#gcode:functions>`__

Calling Files
-------------

To call a separate file with a subroutine name the file the same as your call and include a sub and
endsub in the file. The file must be in the directory pointed to by ``PROGRAM_PREFIX`` or
``SUBROUTINE_PATH`` in the ini file. The file name can include **lowercase** letters, numbers, dash,
and underscore only. A named subroutine file can contain only a single subroutine definition.

Named File Example

::

   o<myfile> call

Numbered File Example

::

   o123 call

In the called file you must include the oxxx sub and endsub and the file
must be a valid file.

Called File Example

::

   (filename myfile.ngc)
   o<myfile> sub
     (code here)
   o<myfile> endsub
   M2

[TABLE]

Subroutine return values
------------------------

Subroutines may optionally return a value by an optional expression at an ``endsub`` or ``return``
statement.

Return value example

::

   o123 return [#2 *5]
   ...
   o123 endsub [3 * 4]

A subroutine return value is stored in the ``<_value>`` `predefined named parameter
<#gcode:predefined-named-parameters>`__ , and the ``<_value_returned>`` predefined parameter is set
to 1, to indicate a value was returned. Both parameters are global, and are cleared just before the
next subroutine call.

Errors
------

The following statements cause an error message and abort the
interpreter:

* a ``return`` or ``endsub`` not within a sub defintion
* a label on ``repeat`` which is defined elsewhere
* a label on ``while`` which is defińed elsewhere and not referring to a ``do``
* a label on ``if`` defined elsewhere
* a undefined label on ``else`` or ``elseif``
* a label on ``else``, ``elseif`` or ``endif`` not pointing to a matching ``if``
* a label on ``break`` or ``continue`` which does not point to a matching ``while`` or ``do``
* a label on ``endrepeat`` or ``endwhile`` no referring to a corresponding ``while`` or ``repeat``

To make these errors non-fatal warnings on stderr, set bit 0x20 in the ``[RS274NGC]FEATURE=`` mask
ini option.