Need info on PyBBIO internals - PWM analogWrite

[kevin-george]

Hi, I've found that the the analogWrite function is using the sysfs interface for generating PWM instead of /dev/mem as mentioned on the wiki. Is this is a work in progress or am i looking at the wrong file?
File i found was -> bbio/platform/beaglebone/bone_3_8/pwm.py

[alexanderhiam]

mmap was used for GPIO and the ADC on the 3.2 kernel, and was never used for PWM. Everything is being done through sysfs now to keep the kernel drivers happy. Where are you seeing that in the wiki?

[kevin-george]

Ohh ok, well i read this on the main wiki page "PyBBIO works by reading and writing directly to the /dev/mem special file, and therefore it needs root privileges to run." and assumed this.
Also, what is this about keeping the kernel drivers happy? I've just started working with eLinux and hence the confusion.

[alexanderhiam]

Hmm... I think I'm a little late answering... sorry about that!

By "keeping the kernel drivers happy" I'm referring to the fact that you don't want to change the state of a hardware subsystem if a currently loaded kernel driver is using it, as it will then be in a different state then the driver thinks it is and bad things will happen.