INFO.txt

Compile the code :
– get the code there : https://github.com/ch-nry/OCS/tree/master
– get the latest version of arduinio IDE (I’m using 1.7.10 from here : http://www.arduino.org/downloads)
– make it work (on linux, I have to change COM1 to /dev/ttyACM0 in the config file, and a $sudo usermod -a -G dialout ). The arduino community is huge, so you will find on the internet how to solve any problem you could face.
– optimize code speed at compilation (change all 3 occurrences of “-Os” to “-O3” in the configuration file : arduino package/hardware/arduino/sam/platfom.txt). This is VERY important. Otherwise, the code will be too slow and the synth will not work properly.
– if needed, change some option in the conf.h file.
– unplug the OCS synth power, and plug the programming usb plug of the arduino to the computer using a micro-usb cable.
– compile and put the code in the arduino

Hacking the code :
You can build new modules, or do anything else you know how to.
Don’t forget to share the result of your hack!

Code explanation :
The code is based on a low priority thread that samples input and computes all modulations, updates filter coefficients, etc.
An interruption stops this thread for every audio sample received from the ADC. This audio loop cannot be interrupted. It generates a sample in about 10µs (+/- 1µs). When finished, the micro-controller goes back to the low priorities thread. This thread loops at about 12KHz. (modulations are computed at 12KHz).
One fader is sampled at every loop of this thread. There are 34 analogue values, so all faders are updated at about 500Hz.

Programming tips :
– Use only unit32_t or int32_t type. Float are prohibited : the micro-controller cannot compute them fast enough.
– The only mathematical instruction to use is addition, subtraction, 32 bit multiplication, 32 bit division and perhaps 32×32->64 bit multiplication (using the assembler routine). Everything else is prohibited since it’s not computed natively on the cortex processor.