regarding open source downloads, please read here below:
oifii 1997: https://oifii.org/oifii/
oifii 2012: https://oifii.org/ns-org/nsd/ar/cp/audio_spi/lib-src/oifii/
oifii 2013: https://oifii.org/ns-org/nsd/ar/cp/audio_spi/lib-src/
oifii 2017: to be release in late 2018 or 2019