Physically modeled guitar strings using the Karplus-Strong algorithm with some extensions by Jaffe & Smith.
The string model is built from primitive digital filters like white noise, delay, fader, lowpass & allpass connected by patch cables that form a feedback loop. The patch configuration is described in
ks_string.v. Individual filters are implemented in
ks_dynamics.v. You may wish to follow the original articles for more details:
Strings can be set up, tuned, plucked or muted via the wishbone bus. The default build contains a single string, but it can be reconfigured for multiple strings with sympathetic resonsances by editing
Being a fully digital design audio is output via the I2S protocol, so you'll need a DAC chip (“soundcard”) such as CS4344, UDA1334A or MAX98357A to get analog output.