How to use GCode to run halcmd?

I have a project that uses GCODE to control all the HAL components. For example, I have a python HAL component, that basically checks its pin values to execute things. Does anyone know how to use GCode to control the customized HAL pin values? Or use GCode to run halcmd?

You can use custom M-codes to issue hal commands to setp a value to a hal pin directly.
linuxcnc.org/docs/html/gcode/m-code.html#mcode:m100-m199
Or you can use M62-M68 to read and write values to hal (using motion pins)