Control I/O from G-code?

I want to control some outputs while running g-code. One example is my spindle, it's connected to an output on the drive of the Y axis of my CNC, how can I turn it on and off when the appropriate spindle commands are executed in a g-code program?

It's a primitive setup right now (until I get communication going to the drive for the spindle) it is one speed, so just a toggle on/off.

I have uses for other outputs (connected to drives) also, like opening and closing clamps, starting air cooling, etc. that would ideally be controlled via g-code as well.

I do have HAL pins for the outputs, I can do a setp <output_pin> [1 | 0] and turn them on and off. Is there a way to achieve the same in running g-code?

If you have hal pins that actually control those extra io pins on your drives. controlling them is as simple as connecting them in hal.

If there is a pin called "output_pin" that starts and stops your spindle, I simply connect that pin to the pin "motion.spindle-on" by adding this line to your hal file.Then an M3 Sn (where n=something other than zero) will turn on the spindle, and an M5 or any of the many other things that turn off the spindle will.

If you have another pin that you want to turn on and off via G-code you can use M62-M65 to control the pins motion.digital-out-NN
linuxcnc.org/docs/html/gcode/m-code.html#mcode:m62-m65
And connecting those pins to what ever pins you need to control.

Very thorough, thank you Todd!