Tandem Z axis suddenly homing in opposite directions

Went down to try to get further on the CNC today and homed my machine as usual. Surprisingly the tandem Z access is now trying to home in the opposite directions. I hadn't changed the configuration or wiring so I'm a little perplexed as to how this suddenly started.

When I access each Z joint the + moves the joint up and - moves the joint down on both sides. Homing however, one goes up and one goes down even though it's setup as a tandem joint.

Z is set up as a 4" height 0 being at the top with a -4" travel. Home towards the positive limit, final home position of 4.

Any thoughts?

hal and ini attached.
Tried rebooting the controller and PC with no change

MIN_LIMIT = -4.0
MAX_LIMIT = 4.001
HOME_OFFSET = 4.000000
HOME_SEARCH_VEL = 0.066667
HOME_LATCH_VEL = 0.016667
HOME_FINAL_VEL = 0.000000
HOME_USE_INDEX = NO
HOME_SEQUENCE = 0

Re: HOME_SEQUENCE = 0 for tandem axis this needs to be a -ve number in both joints.

I don't think -ve zero will work.

Also the jog keys won't jog the correct axis until it is homed.

If linuxcnc thinks you are on a limit switch then it will move backwards.
could this be the problem?
The fact it changed over time leads me to this being likely.

other possibility is not running the config you thought you were.

I've tried a few things here. I reset the HOME_SEQUENCE to -0 which was a suggested change as part of another effort. I've also looked at the limit switches themselves. With a voltage meter I get 12v when depressed and 0v when not. This is as expected because I've wired them backwards and compensated for that in the configuration.

The other oddity that I noticed while troubleshooting is that when I auto home the joints and the Z is doing it's thing going backwards I can manually depress the Z home switch and the gantry doesn't stop moving down. The voltage on the switch does change but the behaviour does not. Does that help?

Thanks

Okay, that's really weird. I went through pncconf again and switched the homing to towards negative limit, saved and reran linuxcnc. From there they both started homing down. Then went back in and switched to home towards the positive limit, saved and restarted. Now they both home in the proper direction at the same time.

I can't for the life of me understand why. I've been through the pncconf a few times and updated it with no affect until I touched that specific setting and re-saved it. Anyways, hopefully this helps someone else out down the road.

Thanks for your help!

Are you sure -0 is valid? I do not think -0 is a negative number
(once parsed and turned into a sequence number) so would not
force synchronized homing

Did you check that (via halmeter or halshow)

joint.3.home-sw-in
and
joint.4.home-sw-in

change appropriately when you activate the Z home switches?

I was too quick to call this resolved.

Once I had the machine running I loaded up the attached g-code for a zero clearance insert and couldn't get it to start. I thought perhaps because I removed the tool change in the pncconf earler but no matter what I did the machine wouldn't move under its own command. I tried restarting LinuxCNC which then meant I needed to rehome. Upon hitting the home all button the damn Z axis started going in the opposite directions again.

G-code attached along with the current ini and hal files

Here's precisely what I did.
1) loaded Linuxcnc
2) home all
3) moved Z down
4) moved X
5) touch off X (touch off button)
6 Moved Y
7) touched off Y
8) moved Z down
9) touched off Z
10) pressed run and nothing happened, no errors, no movement, no noise

Thoughts? This is really frustrating.

Minus 0 is what pncconf writes every time I save the config. I'm not familiar with Halmeter at this point. I'll have a look at how to use that.

Why do you think -0 is a valid home sequence number for synchronized joints?

Edit OK if pncconf uses -0 that's a pncconf bug
(integers like sequence numbers cannot represent -0)

I would renumber the home sequence number starting at -1 for Z

This may not fix all of you issues but will at least
force the Z joints to do synchronized home moves