RepRapFirmware 3.01 and later provide GCode programming constructs to allow conditional execution and iteration, and allow parameter values in GCode commands to be expressions instead of literals.

abort <opt-expression>

This causes all nested macros and the current print file (if any) to be terminated. The expression (if present) is converted to a string, which is included in the message presented to the user and written to the log file.

echo  <expression>, <expression>, ...

At least one expression must be provided. The expressions are converted to strings and written to the console, with a space character between each pair. Example:

echo move.axes[0].homed, move.axes[1].homed, move.axes[2].homed

Starting with firmware 3.4 the output from an echo command can be redirected to a file. To create a file (deleting any existing file of the same name) containing the text resulting from the echo command, use this syntax:

echo ><filename> <expression>, <expression>, ...

where <filename> is either a quoted string or an expression enclosed in { } that evaluates to a string.

To append a line to an existing file (or create a new file if it doesn't already exist), use:

echo >><filename> <expression>, <expression>, ...

There must be no spaces between the > or >> symbol and <filename>. The default folder for the file is /sys.

Example:

echo  >"mymacro.g" "G1 F3000 X"^{move.axes[0].max-10} ; move to 10mm below axis max when the macro was generated
echo >>"mymacro.g" "G1 F3000 Y{move.axes[1].max-10}"  ; move to 10mm below axis max when the macro is executed

The general form of the conditional block is:

if <boolean-expression>
  ...
elif <boolean-expression>
  ...
else
  ...

where as usual the “elif” part can be omitted or repeated, and the “else” part can be omitted. The bodies of the if, elif and else parts may contain ordinary GCode commands and/or program elements. Each line in the body must be indented from the corresponding keyword to indicate the extent of the body. The body ends just before the first line that is not indented.

while <boolean-expression>
  ...

The body must be indented from the while keyword. The body ends just before the first line that is not indented.

Within the while-part and the body, the named constant iterations is the number of loop iterations already completed. So it is zero during the first iteration, 1 during the second, and so on.

A loop may contain one or more break statements, which would normally be inside if-constructs:

while <boolean-expression>
  ...
  if <boolean-expression>
    break
  ...

The break statement transfers control to the line following the end of the loop body.

A loop may also contain one or more continue statements, which would normally be inside if-constructs:

while <boolean-expression>
  ...
  if <boolean-expression>
    continue
  ...

The continue statement increments the iteration counter and transfers control back to the start of the loop, ready to evaluate the while-condition again.

Implemented in RRF 3.3 and later

var <new-variable-name> = <expression>

This creates a new variable called var.<new-variable-name> and initializes it to <expression>. The name must not already be in use. The scope of a local name is the remainder of the block in which it is declared.

Implemented in RRF 3.3 and later

global <new-variable-name> = <expression>

This creates a new variable called global.<new-variable-name> and initializes it to <expression>. The name must not already be in use.

Example:

set global.T1heat=0

Implemented in RRF 3.3 and later

set <existing-variable-name> = <expression>

This re-assigns an existing variable (which must be of the form var.name or global.name) to have the value expression.

Example:

set global.T1heat={heat.heaters[1].active}

Variables must conform to the following naming convention:

• The first character must be a letter
• The remaining characters must be letters, digits or the underscore character
• There is no specific limit on variable length, other than the total length of the expression that uses the variables must be <250 characters

This form:

{ <expression> }

may be used in place of any numeric or quoted string operand within a GCode command. Example:

G1 X{move.axes[0].max-10} Y{move.axes[1].min+10}

Using an expression to replace a parameter latter, or to replace the command number after the initial G or M, is not supported. (so for example G1 {global.extruder_axis}^2 is not supported)

If a parameter of a G- or M-command requires multiple values and you want to use expressions for some or all of them, then when using RRF 3.3 and later the parameter must be expressed like this:

{ <expression_1>, <expression_2>, <expression_3> ... }

For example:

M201 {var.e0Accel, var.e1Accel}

RRF 3.2 in standalone mode only supported this form instead:

M201 {var.e0Accel}:{var.e1Accel}

Tabs and space characters may be used freely between variable names, keywords, literals and other lexical elements to improve readability.

Sub-expressions may be enclosed in { } or in ( ). However, standard CNC GCode uses ( ) to enclose comments. So in CNC mode, RepRapFirmware treats ( ) as enclosing subexpressions when they appear inside { } and as enclosing comments when they do not. Therefore, when RepRapFirmware is running in CNC mode, any use of ( ) to enclose a subexpression or function parameter list must be within an expression enclosed in { }.

Expression length is limited to 250 characters.

The available types of expressions and variables are: bool, int, float, string, DateTime, object and array. The only operations available on values of type object are comparison with null and taking a member. The only operations available on values of type array are taking the length (unary prefix operator #) and indexing (operator [ ] ).

The following implicit type conversions will be performed when necessary:

• from type int to type float
• from any type to string

The following names constants are provided:

Decimal integer, floating point and string literals may be used. There are no literals of other types, however the Boolean constants true and false are available.

Expressions may use the values of any properties in the RepRapFirmware Object Model (OM). See Object Model of RepRapFirmware to see what is available. An object model property selector must evaluate to a single string, numeric or Boolean value, unless it is the operand of the unary # operator in which case it must evaluate to an array or a string.

These are supported in RRF 3.3 running in standalone mode.

The values of global variables that have been created using the 'global 'command can be retrieved using the syntax global.<variable name>. Example:

global defaultSpeed=6000
...
G1 X0 Y0 F{global.defaultSpeed}

Similarly, the values of local variables created using the var command can be retrieved using the syntax var.<variable name>

Use exists{<variable>} to check if a variable is defined (not yet implemented in SBC mode). e.g.

exists(global.defaultSpeed)

Note: In CNC mode, round brackets in a line are treated as enclosing comments. This means that if you use expressions in GCode, if you use round brackets within expressions then the whole expression must be enclosed in { }. This would normally be the case anyway when using expressions as parameters to regular GCode commands, so this only affects the use of round brackets in GCode meta commands such as if, while, var, global, echo and so on. See here for more information.

These are supported in RRF 3.3

It is possible to add additional parameters when calling a macro using M98 or using a macro as a custom gcode.

e.g.

M98 P"macro.g" S100 Y"string"

Within a macro file, parameters that were passed to the macro can be retrieved using the syntax param.<parameter letter> where <parameter letter> is a single uppercase letter.

e.g. (using the macro call from above)

;macro.g
G1 X{param.S}
echo {param.Y}

When using a macro as custom gcode, do not use G, M, N or T as parameters in a custom 'G' gcode file. Do not use G, M or N as parameter in a custom 'M' gcode file. There are no standard G or M commands that use these parameters and RRF will treat the parameter as being the start of the next command.

Where an expression has multiple binary operators of the same precedence and parentheses are not used to specify the order of evaluation, the operators are evaluated from left to right.

Caution! The multiplication operator * will work when it is used anywhere inside an expression or subexpression enclosed in { } but not otherwise. This is because the * character in a line of GCode normally introduces an end-of-line checksum.

The expression <expr1> ? <expr2> : <expr3> evaluates <expr2> if <expr1> is true, otherwise <expr3>. <expr1> must be Boolean. <expr3> may be another ternary expression. The ternary operator has precedence 1.

The following functions are supported, with their conventional meanings:

(Please check the changelog to determine when a particular function was implemented, some functions are implemented in RRF3.1, or 3.2, or later)

Example bed.g file for calibrating a delta printer using conditional GCode. At the start, it homes the printer only if it hasn't already been homed. Then it calibrates the printer by probing a number of points, starting again if probing fails. if calibration yields a standard deviation that is above a limit (set at the end of the loop, in this case >0.03mm), it repeats the calibration process. If calibration fails 5 times for any reason, it quits.

NOTE: If you use this method to iterate the levelling of a bed/gantry mounted on leadscrews (eg Cartesian, CoreXY etc), the maximum deviation corrected is still limited by the S parameter of M671 (default 1mm). If the maximum deviation exceeds this limit, the script will exit with "Error: Some computed corrections exceed configured limit of 1.00mm", as it would if G30 bed levelling was called manually.

; Auto calibration routine for large delta printer
M561                    ; clear any bed transform

; If the printer hasn't been homed, home it
if !move.axes[0].homed || !move.axes[1].homed || !move.axes[2].homed
  G28

; Probe the bed and do auto calibration
G1 X0 Y140 Z10 F10000        ; go to just above the first probe point
while true
  if iterations = 5
    abort "Too many auto calibration attempts"
  G30 P0 X0.00 Y140.00 Z-99999
  if result != 0
    continue
  G30 P1 X70.00 Y121.24 Z-99999
  if result != 0
    continue
  G30 P2 X121.24 Y70.00 Z-99999
  if result != 0
    continue
  G30 P3 X140.00 Y0.00 Z-99999
  if result != 0
    continue
  G30 P4 X121.24 Y-70.00 Z-99999
  if result != 0
    continue
  G30 P5 X70.00 Y-121.24 Z-99999
  if result != 0
    continue
  G30 P6 X0.00 Y-134.85 Z-99999
  if result != 0
    continue
  G30 P7 X-65.57 Y-113.57 Z-99999
  if result != 0
    continue
  G30 P8 X-112.29 Y-64.83 Z-99999
  if result != 0
    continue
  G30 P9 X-130.59 Y-0.00 Z-99999
  if result != 0
    continue
  G30 P10 X-115.90 Y66.91 Z-99999
  if result != 0
    continue
  G30 P11 X-69.45 Y120.29 Z-99999
  if result != 0
    continue
  G30 P12 X0.00 Y70.00 Z-99999
  if result != 0
    continue
  G30 P13 X60.62 Y-35.00 Z-99999
  if result != 0
    continue
  G30 P14 X-52.28 Y-30.19 Z-99999
  if result != 0
    continue
  G30 P15 X0 Y0 Z-99999 S8
  if result != 0
    continue
  if move.calibration.initial.deviation <= 0.03
    break
  echo "Repeating calibration because deviation is too high (" ^ move.calibration.initial.deviation ^ "mm)"
; end loop
echo "Auto calibration successful, deviation", move.calibration.final.deviation ^ "mm"
G1 X0 Y0 Z150 F10000                ; get the head out of the way