PWM from a Linux Daemon, I Told You It Was a Bad Idea, Now Here’s How to Do It

Introduction - Recap what PWM is and why it’s useful - You do PWM the same way on Linux as you would on an Arduino, as we will show - But you have to handle a multi threaded environment, that means jitter

Writing the daemon: - Brief: high level design of my daemon - Brief: how to control GPIO pins on the raspberry pi (memory mapping with /dev/mem, /dev/gpiomem) - Brief: introduction to daemons (fork/exit, start new process group with setsid, close standard file descriptors that were cloned by fork) - Brief: open FIFO, endless loop on main thread waiting for messages, update the control structure based on the control message parameters for the pin, spawn a thread if needed

PWM: - Detailed: how the threads actually control LED brightness, basically each one does a mark/space and turns the LEDs on and off on a 100Hz cycle with varying duty cycle.

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