Hi, Actually I never use Raspberry pi3 before, But As long as it's SPI, the concept is same with another Computer/Microcontroller. Just need to be adapted to Raspberry BSP. Because I have familiar with these peripheral in another MCU and the global concept is same. And I'm not new in developing IC's Library.
So, Let's discuss the detail over chat. Let me help you solve it.
Best Regards,
Rijal