JSON Active Comments

This page describes using Gcode comments to carry JSON commands such that they can extend existing Gcode functions or insert control functions that execute synchronously with the Gcode.

Gcode Comments

Gcode comments in G2 possess a number of features that extend their capabilities beyond classic Gcode. Classic Gcode only defines parentheses comments (...) and message comments (msg...). Additionally, a slash character / in the first character is a block delete, which can be considered a type of comment.

G2 handles comments as so:

• Classic Gcode comments that start with a ( and end with a ) are known as "inline comments" and will be removed, UNLESS they are an active comment

• Gcode Message comments are active comments with the letters msg (case insensitive) immediately following the open parenthesis: (Msg....)

  • The string enclosed by the trailing g and the closing paren will be returned in the next status report as a "msg":"...." tag
  • If there is a space or anything else between ( and the m then it will be treated as a normal comment
  • Only one message comment is allowed per Gcode block

• JSON comments are active comments with JSON immediately inside the parentheses: ({...})

  • JSON comments carry content that GCode can't express, but is intrinsically part of the command in that Gcode block
  • If there's a space or anything else between the ( and the { then it will be treated as a normal comment

• Multiple inline comments (...) are allowed, and active comments (message and JSON) in between will be retained

• Multiple active comments are allowed, and will be combined and treated as if they were separated by commas

  • Ex: M100 ({he1st:200}) ({he2st:210}) will be treated the same as M100 ({he1st:200, he2st:210})
  • Message comments are converted internally to JSON comments, so these may also be mixed with JSON comments

• Comments that start with a semicolon ; end the line -- everything including and after the ; will be ignored, including any active comments. Some Gcode generators use semicolons as comments

• Comments that start with a percent sign % (as some Inkscape Gcode generators do) are converted to semicolons and end the line -- everything including and after the % will be ignored. A percent sign received during a feedhold is treated as a queue flush

• Lines that start with a forward slash / in the first character are block delete lines. These lines are omitted in their entirety

Valid Comment Cases

Valid comment cases	Notes
G0X10	command only - no comment
G0X10 (comment text)	command with comment
G0X10 (comment text	acceptable, but a warning may be issued for the comment not being terminated
G0X10 ;comment text	comment delimited by semicolon
(MSGSend this string)	will report back as "msg":"Send this string"
(comment text)	there is no command on this line
G0 (traverse) X10 (to X ten) Y12 (and Y twelve)	Command G0X10Y12 with multiple inline comments
M100 (set heater temp to 210:) ({he1st:210})	Command with inline comment and active comment

JSON Active Comments

The following Gcode/Mcode commands use JSON active comments

Code	Definition	Notes
M100	Execute from Planner	Execute JSON when the planner reaches it
M101	Wait on Event	Pause execution until condition in JSON is met

Examples

Set heater 1 temperature to 220 degrees

m100 ({he1st:220})

Pause movement until heater 1 is at temperature, then continue

m101 ({he1at:t})