Tool Clamp / Unclamp bit

There isn't a tool clamp/unclamp output from LinuxCNC, as toolchangers are too variable in there sequences.

Take a look at the sim/axis/vismach/vmc_toolchange simulator config, that has both spindle lock and tool clamp outputs. In that case they are handled as part of a sequence encoded in a G-code subroutine:

github.com/LinuxCNC/linuxcnc/blob/master...hange/toolchange.ngc

That uses M64 to output a digital signal to HAL, then waits for comfirmation using M66.

I think that it would certainly be worth trying the PLC code. It should be just as capable of reading/writing HAL pins as the G-code sub.