Tandem Y axis problems

Hello all,

I'm trying to configure PlasmaC with a tandem Y axis (i.e. XYYZ). I'm having a weird issue where when I home then jog the Y axis, the Z axis value changes in QtPlasmaC, often to some absurdly large number. I get a joint following error at the same time. X and Z axes work fine when jogged. I get the same result in Axis and PlasmaC, so I can't blame the GUI.

I've read everything I can find on the subject but for the life of me I can't figure out why I'm having this problem with the attached config. Does anyone have any clue what might be wrong here?

FYI: I'm using a test bench setup with 4 steppers and no limit switches to test out a board I'm developing. That's the 'hotshot' component referred to in the .hal file. I've validated that it returns the correct values many times. I've also tried hacking it to simply return the commanded position as the feedback position. 

Thanks for the reply. Unfortunately that doesn't help. I just uncommented, homed axes, jogged Y. Z DRO jumped to 838860 and a "joint 3 following error" disabled motion. I remain baffled as to what could be causing this.

I guess the board I'm building requires some explanation. The config I posted works great in XYZ mode. I'll post the component code in a minute.

There is no stepgen in the hal file because the TMC5041 drivers I'm using has it built in. It also provides servo-like feedback for steppers as they have some secret sauce for detecting stalls.

Here's the component code. And the drivers I'm using for background: www.analog.com/media/en/technical-docume...atasheet_rev1.16.pdf

As suggested I regenerated the config with Stepconf, then replaced the stepgen and parport stuff with references to my board. I also added HOME_SEQUENCE settings to joints in the INI file. The weird problem with the Z axis DRO value seems to be gone.

Now the Y axis occasionally stops being tandem and only one motor turns. I'm going to debug that then post the configuration when it fully works.