The following are snippets from the solution I used. I'm not entirely satisfied with it, but so far it seems to be robust and I can't figure out anything to do that causes the Z axis to drop out of control. As I proceed with this project I'll be carefully watching it and thinking about any edge cases that are unsafe.
Code:
loadrt xor2
addf xor2.0 servo-thread
loadrt lut5
addf lut5.0 servo-thread
# Used to delay Z brake release before drive is commutating
loadrt timedelay
addf timedelay.0 servo-thread
setp timedelay.0.on-delay 5
setp timedelay.0.off-delay 0
Note: I've never fully embraced HAL, so ignore my arrow directions if they don't make any sense. One day it will all click, I'm sure.
Z_Fault comes from the drive and signals a variety of faults. Whatever the fault, the brake is engaged until things are sorted out.
Z_Commutation_Complete is a signal output by the drive when it's done commutating. This could have been so much easier if I had a signal that told me it WAS commutating and had control of the axis.
Z_Reset is a Mesa card output connected to the drive reset input (on reset the drive does NOT hold the axis in place)
machine-is-enabled is unaltered from linuxcnc
z_brake_delay is a time delayed signal activated either by reset or drive enable. Immediately upon drive enable or reset the drive does not have control of the axis so the brake can't be disengaged. But soon after (about 5 seconds) it has control of the axis and is trying to move it to find out where it is. It can't do this with the brake engaged. So 5 seconds after reset or enable this signal goes high to disengage the brake so long as there is no fault, no reset, and the machine is enabled.
Code:
# Z Axis is more complicated due to commutation and the brake to prevent gravity runaway
net machine-is-enabled => xor2.0.in0
net Z_Reset => xor2.0.in1
net z_enable_xor_reset xor2.0.out => timedelay.0.in
net z_brake_delay <= timedelay.0.out
setp lut5.0.function 0x220000
net z_brake_delay => lut5.0.in-0
net Z_Fault => lut5.0.in-1
net Z_Commutation_Complete => lut5.0.in-2
net Z_Reset => lut5.0.in-3
net machine-is-enabled => lut5.0.in-4
net z_brake_release <= lut5.0.out
net z_brake_release => hm2_7i76e.0.7i76.0.0.output-10
Feel free to point out any potential improvements or major flaws.
