On 1/5/2014 8:57 AM, Thomas Studwell wrote:
> I am currently using debian-7.2-machinekit-armhf-2013-12-02 image, 
> modified for the Xylotex BBB_DB25ee board and I want to change the 
> polarity of the Step pulses (3 axis). Is there a configuration setting 
> to do this? I tried updating my HAL to allocate the pins to GPIO so I 
> could invert with setp but then the stepgen was not happy with this...
> 
> The PRU driver configuration is: 
> CONFIG=prucode=/home/linuxcnc/linuxcnc/rtlib/xenomai/pru_generic.bin 
> pru=1 num_stepgens=3

You can use a negative value for the position scale, which will move the
motor the other direction.  If you actually want the step pin inverted
(ie: mostly high, with a step pulse causing the signal to go low),
you'll have to tweak the code.  This isn't currently supported in the
PRU code (along with up/down mode, and a few other things you can do
with a hostmot2 stepgen).

Also, since the PRU is running the "base thread", instead of the ARM,
you can't use HAL to play with the outputs like you could if it was a
typical x86 system.  Anything dealing with timings faster than the servo
thread needs to be coded on the PRU.

-- 
Charles Steinkuehler
[email protected]

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