This is a hack to drive a stepper motor with acceleration ramps from a BeagleBone using the PRU for real time control.
Development by Stefan Langemark and Håkan Langemark. (Mostly Stefan so far...)

Demonstration on youtube: http://youtu.be/YlDHBbKrRtU

Acceleration ramp maths based on Atmel's AVR446 application note.

Instructions:
The code depends on PyPRUSS by Elias Bakken (https://bitbucket.org/intelligentagent/pypruss).
Install and make sure you can run the examples.

This code is setup to drive GPIO0 pin 27 with a positive flank for each step, and pulse width of 1.9 us, which suits standard pololou stepper drivers.

You need to configure the pin as an output using a device tree overlay. I followed this example:
http://hipstercircuits.com/beaglebone-black-gpio-mux-for-pru-with-device-tree-overlay/
The output will be on P8-17.

Usage:
python stepper.py <num steps> <speed> <accel> <decel>

For example: 500000 steps at medium acceleration up to 100 rad/s = about 16 revs/s (assuming 200 step/rev motor and 1/32 microstepping)
python stepper.py 500000 100 500 500

Known bugs:
Yes.