<p>I thought I am not bad at Google, but simply I am unable to find a G-code for doing circular motion for nozzle cleaning. It is possible to write a simple circular motion in G-code?</p>

To draw a circle, you need to approximate the circle as a sufficient number of line segments. This requires computing or using a table of sine and cosine values for each angle step. Then you just emit a sequence of
```
G1
```
commands.
Some printer firmware also supports arc drawing commands you could use instead in principle, but support is not widespread, and the quality of the results varies enough that I would not recommend trying to do it this way.