PyBBIO
I've spent the semester continuing work on PyBBIO, my Python library for Arduino-style hardware IO support on the BeagleBone. I've made a lot of progress in way of the PyBBIO's structure and control flow, fixing bugs reported through Github's issue tracker, and building up API and extra libraries.
There are two ways in which PyBBIO can be used; it can either be imported into a *.py file and its control loop invoked by calling the run() function, or it can be imported directly into the Python interactive interpreter. There is a some amount of required initialization and cleanup when accessing IO modules (e.g. enabling/disabling module clocks, etc.), so this has to be handled automatically in either case. Here is the code which handles both the interactive initialization and cleanup, as well as the Arduino-style 'main loop':
# The following code detects if Python is running interactively,
# and if so initializes PyBBIO on import and registers PyBBIO's
# cleanup to be called at exit, otherwise it defines the run() and
# stop() methods for the file based control flow:
import __main__
if not hasattr(__main__, '__file__'):
# We're in the interpreter, see:
# http://stackoverflow.com/questions/2356399/tell-if-python-is-in-interactive-mode
bbio_init()
print "PyBBIO initialized"
import atexit
def interactive_cleanup():
bbio_cleanup()
print "Finished PyBBIO cleanup"
atexit.register(interactive_cleanup)
else:
# Imported in a Python file, define run() and stop():
def run(setup, loop):
""" The main loop; must be passed a setup and a loop function.
First the setup function will be called once, then the loop
function wil be called continuously until a stop signal is
raised, e.g. CTRL-C or a call to the stop() function from
within the loop. """
try:
bbio_init()
setup()
while (True):
loop()
except KeyboardInterrupt:
# Manual exit signal, clean up and exit happy
bbio_cleanup()
except Exception, e:
# Something may have gone wrong, clean up and re-raise exception
bbio_cleanup()
raise e
def stop():
""" Preffered way for a program to stop itself. """
raise KeyboardInterrupt # Expected happy stop condition in run()
- edit 12/11 2:46 AM: fixed a couple typos in PyBBIO control loop, so updated here as well.
As PyBBIO's users have started to grow in numbers, I've realized just how valuable Github's issue tracking is (and issue tracking in general). Most of the issues that have been reported have had to do with inconsistencies between Python builds on different versions of the BeagleBone's Angstrom Linux image. Though annoying, through sorting these issues out I've been able to build up an install script which can elegantly handle them, and even patches certain 'broken' Python builds which are missing one of the core modules for compiling Python files. (PyBBIO's closed issues
here.)
The area I've made the most progress in is building the core API for the different IO modules, as well as additional importable libraries for specific tasks and external components. At the time of writing this, the core API covers basic
GPIO, the
analog-to-digital converter,
pulse width modulation,
serial, and most recently a simple
software SPI implementation (the BeagleBone's AM3359 processor includes hardware SPI which I plan to add support for soon). I've also implemented extra libraries for the
ADS786x series ADCs, the
DACx311 series DACs, the
MAX31855 thermocouple amplifier,
servo motors, a library for creating simple custom
web interfaces, and a couple other small utility libraries.
The full API documentation can be found
here.
My latest addition to PyBBIO was a pinout reference for the BeagleBone's expansion headers, which shows all of the pins which are supported by PyBBIO. I'll continue to add to the image as I add support for more IO modules.
Links:
