HAL trigger M code

Is there a way to have a HAL input pin to run a M code?

Yes depending on exactly what you want to do. As long as you don't need your hal input to trigger the M-code while in auto mode (while g-code is running) you can use a Halui MDI command.
linuxcnc.org/docs/2.7/html/config/ini-co....html#_halui_section
In your ini file under [HALUI] you add
MDI_COMMAND = xxxxx
where xxxxx is the MDI command you want to execute when the hal pin "halui.mdi-command-<nn>" turns true (nn is the number of the command 00-63). You just list your MDI commands in the ini and the order they are listed is their number.

If you do need to be able to activate it while a program is running there are other ways to skin this cat. (most involve doing what ever your M-code does directly without using the M-code.)

Thanks guys!