Tandem axis with shared home

After many years on 2.7, I'm finally getting to set up 2.9

I have a tandem Y axis, each with its own home/ min limit switch, but shared input. I.e the separate physical switched are connected to the same input pin on my Gecko G540. Do I need to give Y and tandem Y separate home inputs? When I tried homing, the gantry traveled to the end, then Y reversed direction while Y tandem kept crashing. 

Thanks,

Any help appreciated

Y and Y-tandem must use separate home switch inputs if they are to square themselves in the homing process. (2 switches connected to a single input is seen as a single switch by Linuxcnc.) Otherwise I think it could be possible to use a common input, but then they are just both going to home off of which ever side hits the home switch first. If configured this way both y axis will need to just maintain the same distance relative to each other as when they are first powered up and you will not be able to do any useful squaring, because you will never know where each axis is relative to the other one. The possible exception to this would be if these are servos and you home to the encoder indexes. (Then I think a single home switch might work.)

Now as to why your 2nd axis is crashing, I can not say for sure without more information. Most likely some kind of configuration error. But I can't begin to guess without knowing more, (such as seeing your config files.) But I do think I can confidently say that it wouldn't simply be because you have both Y homes connected to a single input, there is more to it than that. (Most likely it is because the home input for the 2nd Y isn't actually connected to it in the hal config, but there are other posibilities.)

Thanks for the reply. You were right on both counts: I needed a separate input for squaring, and I had another issue in config - X and Y 1 home/limit switches were mixed up, causing limit errors. I'm now able to home all axes.

1 thing to note. I tried using stepconf to set up the Y2 min limit/home, but it kept it assigning it as for axis A.
Had to change
     net min-home-a      <= parport.0.pin-12-in-not
to
     net min-home-y2     <= parport.0.pin-12-in-not

and add 
     net min-home-y2 => joint.2.home-sw-in
     net min-home-y2 => joint.2.neg-lim-sw-in

However, a couple of additional issues as a result:
1. I can't jog Y. I get "Cannot jog joint 1 because home_sequence is synchronized (-1)"
2. PgUp and PgDn don't jog Z. Instead, I get the same message as above, but for joint 2.

Note: joint 0 = X, joint 1 = Y1, joint 2 = Y2, joint 3 = Z

So it seems that there's some confusion about joint assignment. I've attached my ini and hal files in case anyone can help.

Starting to see light at the end of the tunnel. [ and ] do indeed allow me to jog Z prior to homing. Once all axes are homed, joint0 - joint3 are replaced onscreen by X Y Z. I am also able to jog X and Y using arrow keys. Using PgUp and PgDn highlights the radio button for Z, but nothing happens. Also, I am completely unable to move that axis using any buttons or commands. I feel like there's something simple I'm not seeing.

Solved! My limit settings under [AXIS_Z] were different than [JOINT_3]. Specifically, it had a positive limit of 0.01. (Acceleration was also ludicrously high, causing it to stall).

I have a few more settings to tweak, but it is now operational. Thanks for the help!