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[[cha:o-codes]]
= O Codes(((O Codes)))

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== Use of 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
----

[[ocode:comments]]
== Comments(((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.

[NOTE]
Using the lower case 'o' makes it easier to distinguish from a 0
that might have been mistyped. For example 'o100' is easier to
see than 'O100' that it is not a '0'.

[[ocode:subroutines]]
== Subroutines(((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 <<gcode:g53,G53>>, <<gcode:g0,G0>> and <<mcode:m2-m30,M2>> 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 <<gcode:binary-operators,Binary Operators>> and <<sec:overview-parameters,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])
    (DEBUG, parameter 3 is [#3])
o100 endsub

o100 call [100] [2] [325]
----

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 can 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.

[[ocode:fanuc-style-programs]]
=== Fanuc-Style Numbered Programs(((Subroutines,M98,M99)))

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.

[NOTE]
Numbered main and subprogram definitions and calls differ from
traditional rs274ngc both in syntax and execution.  To reduce the
possibility of confusion, the interpreter will raise an error if
definitions of one style are mixed with calls of another.

.Numbered Subprogram Simple Example
[source,{ngc}]
----
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
[source,{ngc}]
----
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`.

[[ocode:looping]]
== Looping(((Subroutines,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.

[[ocode:conditional]]
== Conditional(((Subroutines,Conditional Loops)))

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 conditions may be tested for by 'elseif' statements until the
'else' path is finally executed if all preceding conditions 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
----

[[ocode:repeat]]
== Repeat(((Subroutines,Repeat Loop)))

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.

.Example with 'repeat'
----
(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)
----

[[ocode:indirection]]
== Indirection(((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:

* <<sec:overview-parameters,Parameters>>
* <<gcode:expressions,Expressions>>
* <<gcode:binary-operators,Binary Operators>>
* <<gcode:functions,Functions>>

[[ocode:calling-files]]
== Calling Files(((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
----

[NOTE]
The file names are lowercase letters only so 'o<MyFile>' is converted to 'o<myfile>'
by the interpreter. More information about the search path and options for the
search path are in the INI configuration section.

== Subroutine return values(((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>'
<<gcode:predefined-named-parameters,predefined named parameter>> , 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.

[[ocode:errors]]
== Errors(((O-Code Errors)))

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

 - a `return` or `endsub` not within a sub definition
 - 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.

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