gcode-interpreter.md (3060B)
1 --- 2 title: "Writing a G-code Interpreter" 3 date: 2024-10-23T16:29:40-07:00 4 tags: [G-Code, Lasers, C] 5 draft: false 6 --- 7 8 I'm currently working on a control system for a laser galvanometer (galvo) that 9 I want to use in a stereolithography (SLA) resin printer. I don't want to write 10 a custom slicer, as I feel like model slicing can be incredibly complicated and 11 existing free software (Cura, Slic3r, etc.) has many advanced features I don't 12 want to reimplement. However, this means my control system needs to understand 13 G-code, the language that these slicers output. 14 15 As stated on the [reprap wiki](https://reprap.org/wiki/G-code), "G-code is a 16 list of fields that are separated by white spaces or line breaks. A field can 17 be interpreted as a command, parameter, or for any other special purpose." For 18 now, we'll ignore any special purposes. Here is an example of G-code that 19 describes a movement of the tool/hotend/laser to a specific location: 20 ```gcode 21 G1 X10.4 Y7.4 Z8.3 22 ``` 23 I was able to parse commands with parameters using a two-stage procedure: 24 25 1. Retrieve the next white-space delimited token. 26 2. Accumulate tokens until two separate command tokens are found. 27 28 This second step is important because we can't begin executing a command until 29 we've found all of its parameters and we don't know if we've found all of its 30 parameters until we find the next command. 31 32 Once a command and all of its parameters have been parsed, it is passed to the 33 controller which updates the state of the machine. For each command that the 34 controller receives, it has to update its internal state, and in the case of 35 physical movement commands, send the proper signal to the laser galvo. Most 36 physical movement commands utilize interpolation so a timed control loop is 37 utilized to ensure the laser follows as close to the intended path as possible. 38 39 ## System Diagram 40 ```goat 41 more params? 42 .----------------------------. 43 | | 44 v | 45 .-----------. token .-------------. 46 | tokenizer | --------------> | accumulator | 47 '-----------' '-------------' 48 | 49 command w/ params | 50 .----------------------------' 51 | 52 v 53 .--------------. ctrl signal .-------------. 54 | controller | -------------> | laser galvo | 55 '--------------' '-------------' 56 ``` 57 58 ## Source Code 59 The source code for the G-code interpreter can be found 60 [here](https://git.christianermann.dev/gcode-interpreter). You may have issues 61 accessing the link if your ISP doesn't support IPv6 yet. 62 63 Also, the names in the code are different than what's shown in the diagram, so 64 here's the mapping to help out with understanding the code: 65 66 | Diagram | Source File | 67 | :---------- | :---------- | 68 | tokenizer | token.c | 69 | accumulator | command.c | 70 | controller | machine.c | 71 72 I'll try to keep this updated if the mapping changes as I continue to work on 73 this project. 74