Wait for spindle-halt signal before reversing spindle direction

Hi all,

I have a setup where the spindle drive provides a spindle-halt signal when the spindle has fully stopped. I’d like to make sure LinuxCNC does not reverse the spindle direction (i.e. switch between M3 and M4) until this spindle-halt signal is true.

Is there a built-in way in LinuxCNC to delay or block a direction change until this signal becomes active? Or do I need to handle this myself, for example using HAL logic or some custom component?

Curious to hear how others have tackled this.

Thanks in advance.

Do you have a spindle encoder? 
(it might be a bit easier in hal knowing the velocity)

Also maybe this could be done in the g code with 
m5 m66 

In that case it seems like writing a custom component is the best choice. 
I'm just getting into writing custom realtime components, so this might be a nice exersize.

I can post the link here when I'm done with it if you guys are interested.

This circuit will prevent the spindle direction from changing so long as the spindle is not stopped:
www3.langdonstaab.ca/Spindle%20direction%20circuit.png

(Just an idea)