commit 6db462fd21624cce1b3069d31f66ed0a08b24dc4
parent ef6a32b5d6e2ca58b0f892014a096e4ff8017671
Author: Christian Ermann <christianermann@gmail.com>
Date: Tue, 12 Nov 2024 12:58:30 -0800
Add 'Writing a G-code Interpreter'
Diffstat:
1 file changed, 74 insertions(+), 0 deletions(-)
diff --git a/content/posts/gcode-interpreter.md b/content/posts/gcode-interpreter.md
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+---
+title: "Writing a G-code Interpreter"
+date: 2024-10-23T16:29:40-07:00
+tags: [G-Code, Lasers, C]
+draft: false
+---
+
+I'm currently working on a control system for a laser galvanometer (galvo) that
+I want to use in a stereolithography (SLA) resin printer. I don't want to write
+a custom slicer, as I feel like model slicing can be incredibly complicated and
+existing free software (Cura, Slic3r, etc.) has many advanced features I don't
+want to reimplement. However, this means my control system needs to understand
+G-code, the language that these slicers output.
+
+As stated on the [reprap wiki](https://reprap.org/wiki/G-code), "G-code is a
+list of fields that are separated by white spaces or line breaks. A field can
+be interpreted as a command, parameter, or for any other special purpose." For
+now, we'll ignore any special purposes. Here is an example of G-code that
+describes a movement of the tool/hotend/laser to a specific location:
+```gcode
+ G1 X10.4 Y7.4 Z8.3
+```
+I was able to parse commands with parameters using a two-stage procedure:
+
+ 1. Retrieve the next white-space delimited token.
+ 2. Accumulate tokens until two separate command tokens are found.
+
+This second step is important because we can't begin executing a command until
+we've found all of its parameters and we don't know if we've found all of its
+parameters until we find the next command.
+
+Once a command and all of its parameters have been parsed, it is passed to the
+controller which updates the state of the machine. For each command that the
+controller receives, it has to update its internal state, and in the case of
+physical movement commands, send the proper signal to the laser galvo. Most
+physical movement commands utilize interpolation so a timed control loop is
+utilized to ensure the laser follows as close to the intended path as possible.
+
+## System Diagram
+```goat
+ more params?
+ .----------------------------.
+ | |
+ v |
+ .-----------. token .-------------.
+ | tokenizer | --------------> | accumulator |
+ '-----------' '-------------'
+ |
+ command w/ params |
+ .----------------------------'
+ |
+ v
+.--------------. ctrl signal .-------------.
+| controller | -------------> | laser galvo |
+'--------------' '-------------'
+```
+
+## Source Code
+The source code for the G-code interpreter can be found
+[here](git.christianermann.dev/gcode-interpreter). You may have issues
+accessing the link if your ISP doesn't support IPv6 yet.
+
+Also, the names in the code are different than what's shown in the diagram, so
+here's the mapping to help out with understanding the code:
+
+| Diagram | Source File |
+| :---------- | :---------- |
+| tokenizer | token.c |
+| accumulator | command.c |
+| controller | machine.c |
+
+I'll try to keep this updated if the mapping changes as I continue to work on
+this project.
+
