homing: bound the homing moves, return from a failed latch move

[grandixximo]

Every homing move is planned to twice the joint's travel. With a dead home switch the search runs until a limit switch stops it, or into the end of the travel when the limit switch doubles as the home switch and is ignored. A switch stuck on sends the initial back-off the same way at search speed, which on a Z axis with its switch at the top means down into the table. A switch that fails after its first trip sends the latch move the same way at latch speed. Operators who retry the homing drive the joint further with every attempt.

This adds two [JOINT_n] keys, both defaulting to 0, which keeps today's behaviour:

• HOME_SEARCH_DIST: the farthest the search move may travel without finding the switch.
• HOME_LATCH_DIST: the farthest each of the moves made next to the switch may travel: the back-off waiting for the switch to clear, the latch move, and the index pulse search. A few times the trip overshoot (search speed squared over twice the acceleration) plus the width of the switch's active zone covers them; with an index it must also cover one encoder revolution.

A search that runs out stops where it is and the homing is aborted with an error; the next attempt searches on from there, since a search may legitimately need the whole travel and a joint that has not found its switch yet is no worse off further along. The real use is a continuous rotary joint: its soft limits sit far apart, so today a dead switch spins it until someone hits estop; HOME_SEARCH_DIST a little over one revolution turns that into an abort after one turn.

When one of the moves bounded by HOME_LATCH_DIST runs its full length the joint reports which move, moves back to where that move began at the speed of that move, and the homing is aborted. The machine stays on. The other joints of the sequence stop at once, and the joints synchronized with it (negative HOME_SEQUENCE) move back to the start of their own current move too, so a coupled pair ends where it started. A joint homed repeatedly against a stuck or intermittent switch therefore stays put instead of creeping. A limit switch hit during the return aborts as before.

tests/home-dist covers a dead switch, a switch stuck on, a switch that dies after its first trip, and a synchronized pair with both switches stuck on: the search stops at its bound, the other moves come back to where they began, the expected message is reported and the machine stays on.

The homing module interface gains the two distances in set_joint_homing_params(); homecomp.comp is updated.

[grandixximo]

@Sigma1912 is the other one #4577 😁