What's the function of main MPU here? Does it store some data into its on-chip FLASH memory?
What's the function of PHY here? Why do you need it?
I'm sorry for bothering you.
Frankly speaking, I want the usability like the ALFAT chip which offers physical connection (USB Full-speed) and logical connection (handling of FAT32) together by the EZUSB chip (USB Hi-speed or faster).
You can go through the datasheets of the following Cypress, an Infineon Technologies Company, products which support a SD interface:
1.) SD2 for USB 2.0 mass-storage controller: https://www.cypress.com/file/123391/download
2.) SD3 for USB 3.0 mass-storage controller: https://www.cypress.com/file/123816/download