ESP32 CD Changer emulator with weird SPI like interface

[Maroka]

I'm currently trying to emulate an old car cassette player's cd changer interface with an ESP32 so I can use it to play music over Bluetooth. I've read the documentation for the SPI master and slave drivers for the ESP32 and none of them seem to fit this weird protocol that this player uses. It is sort of like an SPI, but the clock seems to be generated by whichever device is sending the data and the communication happens over a single wire (Half Duplex). Is my only option a "software" SPI? There's a guy who has documented the handshake and some other transactions and actually sells modules for this same type of cassette player: https://maakbaas.com/bluetooth-cd-chang ... prototype/

I e-mailed him and he is actually a really nice person and mentioned that the CS line is also used as a "data received" logic and some other specifics. While I am aware I can just buy the module, since it's very inexpensive for the amount of work he actually put into it, I wanted to try and do it my self and maybe turn it into my university graduation project while also adding the ability to read files off of an SD card.

I have tried some variants like a while loop when the CS line is low and reading the data on every high clock pulse, but my code seems to be stuck in the while loop indefinitely.

Could somebody point me in the right direction here? I will attach some logic analyzer screenshots to better visualize the communication.

logic.png (28.65 KiB) Viewed 1083 times

logic2.png (41.2 KiB) Viewed 1083 times