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Linux kernel driver for the Broadcom 2708 PWM peripheral, for use with WS2812 LED strips. Author: Bart Coppens

This project was inspired by Jeremy Garff's code (https://github.com/jgarff/rpi_ws281x) which does roughly the same, but all in userspace. I didn't like the
idea of userspace doing DMA and driving my peripherals without the kernel's knowledge, and this was a nice reason to write a kernel
driver and experiment with it. (All in all I'm not entirely happy with the result, because it's still accessing/modifying some registers without
using/informing other parts of the platform drivers, but it doesn't really seem they were written with that in mind...)

Tested on my Raspberry Pi B+ with an Adafruit NeoPixel Ring with 16 WS2812 LEDs.

Directory structure:
linux/ Linux kernel module, and the required (small) kernel patch for kernel 3.16.5
lib/ Code to access the kernel module's character device
* apps/ Test example using the code in lib/ to drive a NeoPixel ring:
- ws2812_bcm2708_demo: a very simple demo that does some animations with color transitions
- clock: a simple clock app
- stress: a stress test for the irq

Build instructions:
Build a patched 3.16.5 kernel
build the kernel module:
cd pwm-bcm2708/linux
ARCH=arm CROSS_COMPILE=${CCPREFIX} KERNELDIR=${KERNEL_SRC}/ make
where CCPREFIX is /path/to/crosscompiler/arm-unknown-linux-gnueabi-
Build the libs and demo app:
cd pwm-bcm2708/
mkdir build ; cd build
CC=arm-unknown-linux-gnueabi-gcc CXX=arm-unknown-linux-gnueabi-g++ cmake .. && make
Copy the files over to your Pi
insmod pwm-bcm2708.ko
mknod dev_pwm c grep pwm /proc/devices | cut '-d ' -f1 0
build/apps/ws2812_bcm2708_demo dev_test

TODOs:
Remove the requirement for the kernel patch
Clean up the code some more
* Allow up to two independent output channels being driven (to be tested if I ever get a second ring :-))

Sources:
https://github.com/jgarff/rpi_ws281x
https://github.com/hermanhermitage/videocoreiv/wiki