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This is an RTOS developed by myself, with some code taken from FreeRTOS. This is some of the most difficult code I have ever written, although it really doesn’t do anything useful. Man, context switching in C can be a bear! It’s like a programatic buffer overflow! (seriously, you do a function call and just pop off enough stuff to overwrite the instruction pointer).

In CS 504:Real Time Operating Systems, the class built a functional Real Time Operating system based on the UIK API. In my implementation, I heavily relied on the source code of FreeRTOS. The process focused primarily on demonstrating the atmel processor, multitasking, and and basic interprocess communication, which are fundamental parts of an RTOS. In this project, the same problems are achieved with a very different architecture. Namely, all the first programming projects – generating a sound wave, counting LEDs, timing how long buttons were pressed, and handling hardware events – were programmed similarly and multi-tasked on the propeller chip. This project included interfacing with the ntsc and peripheral drivers, writing a sound driver, learning spin and propeller assembly, and comprehending the propeller architecture.

A musical “note” is a waveform that has a certain fundamental frequency. A perfect sine wave consists only of the fundamental frequency, and sounds very “pure” or mellow, like a flute. For this project, you are to use interrupts to generate the notes of a musical scale, while at the same time using another interrupt to update a count. We will generate square waves by toggling a bit within a port on and off. Specifically, your program should play the notes from middle C to the next higher C, each of approximately one second in duration. These notes should be playing at the same time that an 8-bit binary count is being displayed in the LED’s, updating at approximately 1/4 second.

The purpose of this assignment is to give you experience with the AVR’s timers and the use of interrupts. You are to repeat assignment #1, this time performing the timing using an interrupt-driven timer. You are to write an interrupt service routine (ISR) for one of the hardware timers on the AVR. Each time the timer interrupts, you should update a counter variable. Then, when determining the amount of time that the switch is held down, use the counter value. Then, use the counter again to determine how long to turn on the LED. As before, in addition to writing the code, determine the size of the code in your program, including main and the ISR.