Changes

*[https://github.com/libsidplayfp/SID_schematics/wiki SID internals documentation]

*[https://www.oxyron.de/html/registers_sid.html Oxyron SID reference]

*[https://www.hvsc.c64.org/ High Voltage SID Collection]

*[https://www.wothke.ch/tinyrsid/index.php webSID] Online SID chip emulator