Expressions and flow control

grblHAL supports parameters, expressions and flow control, LinuxCNC style (with some limitations), if enabled in the config file or in builds made with the Web Builder when RS274 NGC expression support is enabled in the Advanced features tab.

Flow control is limited if streaming G-code from a sender, full support is only available in macros stored on a SD card or in the littlefs filing system.

Discussion

Follow or comment in this discussion if you want to know more.

Comments with parameter substitution

Numbered and named parameters referenced in the comment string will be substituted in the generated output.

(print, ...)

Example:

(print, metric mode: #<_metric>, coord system: #5220)

outputs

[MSG:metric mode on: 1, coord system: 1]

when metric mode (G21) is on and the current coordinate system is G54.

(debug, ...)

Output from this comment is controlled by setting $534 - set to 1 to enable 0 to disable (default).
Example:

(debug, metric mode: #<_metric>, coord system: #5220)

outputs

[MSG:metric mode on: 1, coord system: 1]

when metric mode (G21) is on and the current coordinate system is G54.

Generate error with user defined message

(abort, ...)

This will output the supplied message followed by raising error 253 thus terminating any running gcode.
Available from 20241025.

Example:

#200=123.456
...
(abort, Something went wrong, parameter 200=#200)

outputs

(MSG:Error: Something went wrong, parameter 200=123.456)
error:253

Parameters (variables)

All predefined parameters defined in NIST RS274NGC version 3 (ref section 3.2.1) are implemented.
Most additional predefined parameters defined by LinuxCNC (ref section 5.2.3.1) are implemented.

Numbered parameters passed as arguments to G65 macro call

Word	Variable	Word	Variable	Word	Variable
A	#1	I	#4	T	#20
B	#2	J	#5	U	#21
C	#3	K	#6	V	#22
D	#7	M	#13	W	#23
E	#8	Q	#17	X	#24
F	#9	R	#18	Y	#25
H	#11	S	#19	Z	#26

Syntax: G65 P<id> (A- B- C- ...)

NOTES: Axis words ABC and UVW are only available if the corresponding axes are enabled.

Inbuilt G65 macros

G65P1Q<n> - read numeric setting value. <n> is the setting number.

G65P2Q<tool>R<axis> - read tool offset from tool table. <tool> isthe tool number, <axis> is the axis number: 0 = X, 1 = Y, ...

G65P3I<n>[S<m>] - get parameter value. <n> is parameter number. The optional S word can be used to set parameter <m> = <n>, if not given the returned value is stored in the _value parameter.

G65P3I<n>Q<value> - set parameter value. <n> is the parameter number, <value> is the value to set it to.

The reasoning behind having the P3 macro is that it can be used to simulate arrays, this since <n> and <m> can both be expressions.

NOTE: Inbuilt macros will set the _value_returned parameter to 1 if a value is returned, the value is then stored in the _value parameter.

Numbered parameters

Parameters	Usage	Persistent
31 - 5000	User defined parameters, defaults to 0.	No
5061 - 5069	Coordinates of a G38 probe result (X, Y, Z, ...) .	No
5070	G38.3 and G38.5 probe result: 1 if successful, 0 if not.	No
5161 - 5169	G28 coordinates (X, Y, Z, ...).	Yes
5181 - 5189	G30 coordinates (X, Y, Z, ...).	Yes
5210	1 if G92 offset active, 0 if not.	Depends on $384 setting
5211 - 5219	G92 offset (X, Y, Z, ...).	Depends on $384 setting
5220	Coordinate system number for G54 - G59.3, 1 - 9.	Yes
5221 - 5229	Coordinate system 1, for G54 (X, Y, Z, ...).	Yes
5241 - 5249	Coordinate system 2, for G55 (X, Y, Z, ...).	Yes
5261 - 5269	Coordinate system 3, for G56 (X, Y, Z, ...).	Yes
5281 - 5289	Coordinate system 4, for G57 (X, Y, Z, ...).	Yes
5301 - 5319	Coordinate system 5, for G58 (X, Y, Z, ...).	Yes
5321 - 5329	Coordinate system 6, for G59 (X, Y, Z, ...).	Yes
5341 - 5349	Coordinate system 7, for G59.1 (X, Y, Z, ...).	Yes
5361 - 5369	Coordinate system 8, for G59.2 (X, Y, Z, ...).	Yes
5381 - 5389	Coordinate system 9, for G59.3 (X, Y, Z, ...).	Yes
5399	Result from last M66, wait for input. -1 if timed out.	No
5420 - 5427	Current position including all offsets (X, Y, Z, ...).	No
5599	Debug output, 1 if enabled else 0.	Yes

Predefined named parameters

Name	Usage	Comment
_vmajor	Major grblHAL version number, currently 1.1.
_vminor	Minor grblHAL version number, from build date (YYMMDD).	Available from 20241025.
_line	Current G Code line number.
_motion_mode	Current motion mode.	See 1 below.
_plane	Current plane: 170 - G17, 180 - G18, 190 - G19.
_ccomp	Active cutter compensation: 400 - G40.
_metric	1 if G21 is active, 0 if not.
_imperial	1 if G20 is active, 0 if not.
_absolute	1 if G90 is active, 0 if not.
_incremental	1 if G91 is active, 0 if not.
_inverse_time	1 if G93 is active, 0 if not.
_units_per_minute	1 if G94 is active, 0 if not.
_units_per_rev	1 if G95 is active, 0 if not.
_coord_system	Current coordinate system: 540 - G54, 550 - G55, ...
_tool_offset	1 if G43 is active, 0 if not.
_retract_r_plane	1 if G98 is active, 0 if not.
_retract_old_z	1 if G99 is active, 0 if not.
_spindle_rpm_mode	1 if G97 is active, 0 if not.
_spindle_css_mode	1 if G96 is active, 0 if not.
_ijk_absolute_mode	1 if G90.1 is active, 0 if not.
_lathe_diameter_mode	1 if G8 is active, 0 if not.
_lathe_radius_mode	1 if G7 is active, 0 if not.
_spindle_on	1 if spindle is running (M3 or M4), 0 if not.
_spindle_cw	1 if spindle is running clockwise (M3), 0 if not.
_mist	1 if M7 is active, 0 if not.
_flood	1 if M8 is active, 0 if not.
_speed_override	1 if M48 or M50P1 is active, 0 if not.
_feed_override	1 if M48 or M50p2 is active, 0 if not.
_adaptive_feed	Always 0.
_feed_hold	1 if M53.1 is active, 0 if not.
_feed	Current value of F.	Not the actual feed rate.
_rpm	Current value of S.	Not the actual RPM.
_x	Current X coordinate including all offsets.	Same as #5420.
_y	Current Y coordinate including all offsets.	Same as #5421.
_z	Current Z coordinate including all offsets.	Same as #5422.
_a	Current A coordinate including all offsets.	Same as #5423.
_b	Current B coordinate including all offsets.	Same as #5424.
_c	Current C coordinate including all offsets.	Same as #5425.
_u	Current U coordinate including all offsets.	Same as #5426.
_v	Current V coordinate including all offsets.	Same as #5427.
_w	Current W coordinate including all offsets.	Same as #5428.
_abs_x	Current absolute X coordinate (G53).
_abs_y	Current absolute Y coordinate (G53).
_abs_z	Current absolute Z coordinate (G53).
_abs_a	Current absolute A coordinate (G53).
_abs_b	Current absolute B coordinate (G53).
_abs_c	Current absolute C coordinate (G53).
_abs_u	Current absolute U coordinate (G53).
_abs_v	Current absolute V coordinate (G53).
_abs_w	Current absolute W coordinate (G53).
_current_tool	Number of the tool in the spindle.	Same as #5400.
_current_pocket	Always 0.
_selected_tool	Current value of T.	Default -1.
_selected_pocket	Always -1.
_value	Return value from the last G65 macro call.	Set to 0 on entry.
_value_returned	1 if last G65 macro call returned a value, 0 if not.
_call_level	Current nesting level for G65 macro calls or O subroutines.

¹ Motion modes:

Mode	Value
G1	10
G2	20
G3	30
G33	330
G38.2	382
G38.3	383
G38.4	384
G38.5	384
G5	50
G5.1	51
G73	730
G75	760
G80	800
G81	810
G82	820
G83	830
G85	850
G89	890

Operators and precedence

Operators	Precedence
**	Highest
*, / and MOD
+ and -
EQ, NE, GT, GE, LT and LE
AND, OR and XOR	Lowest

Functions

Name	Result	Comment
ABS[arg]	Absolute value
ACOS[arg]	Inverse cosine
ASIN[arg]	Inverse sine
ATAN[arg]/[arg]	Four quadrant inverse tangent
COS[arg]	Cosine
EXISTS[arg]	Named parameter exists
EXP[arg]	e raised to the given power
FIX[arg]	Round down to integer
FUP[arg]	Round up to integer
LN[arg]	Base-e logarithm
ROUND[arg]	Round to nearest integer
SIN[arg]	Sine
SQRT[arg]	Square root
TAN[arg]	Tanget
PRM[arg]	Value of numeric setting2	Available from 20241025.
PRM[arg,bit]	Value of bit in integer setting2	Available from 20241025.

Flow control statements

Statement	Local file	Streamed G-Code	Comment
if <expr>	yes	yes
elseif <expr>	yes	yes
else	yes	yes
endif	yes	yes
do	yes	no
continue	yes	no
break	yes	no
while <expr>	yes	no
endwhile	yes	no
repeat <expr>	yes	no
sub	yes	no
endsub	yes	no
call	yes	no
return [<expr>]	yes	no
alarm <expr>	yes	no	<expr> must evaluate to a valid alarm code2
error <expr>	yes	no	<expr> must evaluate to a valid error code2

² grblHAL specific extension.

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2024-10-24