Open Source implementation of a Digital Guitar Effects Pedal.
You need the ARM GNU toolchain. The file install.sh will download the 2020q2
version of the toolchain from ARM's website as a tarball, uncompress it and
move the binaries to somewhere they can be executed.
If you have OpenOCD installed 'make program' can be used to flash the .bin file to the board. OpenOCD must be installed with stlink enabled.
The pedal is designed in such a way that various different transformations can be applied to the incoming signal.
There are three threads of execution. Input, Output and Transform.
The Input thread is triggered with by a timer (in the case of synthesized input) or by the ADC (in the case of sampling a real input signal through the ADC).
The Output thread is triggered by a timer. Whenever there is a valid output value the output thread will start generating that value using PWM.
The Transform thread is ran from the main loop. If there is data sitting in the input buffer, it will move it into the transform buffer. If there is enough data in the transform buffer, it will perform the currently assigned transformation and put the output into the output buffer. The main loop will do other things such as read from the CLI.
Input Source -> Input Buffer -> Transform Buffer -> Transform is Applied -> Output Buffer -> Output Source
The output source (PWM) is expected to be connected to an external amplifier. For my testing I use a standard Guitar Amplifier.
The input source is expected to just be the ground and data from a standard guitar / music cable. Though there is also an option to synthesize the input. Currently you are only able to synthesize a constant tone.
I used many open source projects and tutorials to help me with this project.
[szczys/stm32f0-discovery-basic-template] (https://github.com/szczys/stm32f0-discovery-basic-template)
I used this project for the basic libraries STM libraries and the nice Makefile that Mike put together. This allowed me a base project to start with using OpenOCD to program the board.
[mblythe86/stm32f0-discovery-basic-template] (https://github.com/mblythe86/stm32f3-discovery-basic-template) I used Matt's fork of the project as a reference for adding OpenOCD debugging using the SWD on the STM32F0 chip. This enabled me to get through quite a few bugs!
[Sash's Website] (http://www.sasabremec.com/) Sash had a nice tutorial on using USART with an STM32F0308 MCU that helped me through a problem I was having.
[Nano Age's Website] (http://blog.nano-age.co.uk/) I'm not sure of the name of the author of Nano Age, but they provided a nice detailed guide detailing how to write the systemcalls that allow you to call printf (and other stdlib functions) on a baremetal card. You can checkout that tutorial here