automatic tool change

viski wrote:

So how to start procedure for tool change? how the software will know when requested tool is in the position?

This is a big subject, and there are nearly as many answers as there are toolchangers.
You don't even have to use Ladder/plc. Some toolchangers are controlled by HAL components written in "comp"
(example: wiki.linuxcnc.org/uploads/enshu.comp )

The basic sequence is that on the T command LinuxCNC sets the iocontrol.0.tool-prepare (bit) HAL pin, with the requested slot in iocontrol.0.tool-prep-pocket and the requested tool in iocontrol.0.tool-prep-number
Then on M6 the iocontrol.0.tool-change bit is set. The toolchanger can then do its stuff, setting iocontrol.0.tool-changed to indicate completion.

If your tool-change is describable by G-code commands then you can also do it by remapping M6 to a G-code subroutine, but I suspect that your system is not that simple.

Note that LinuxCNC requires a T, M6 and G43 to perform a full tool change. There are ways to make it all happen on T, but if you can live with the three-command sequence (I do) it makes things simpler.