SX2 will handle all standard USB device requests, except for halt endpoint, stall endpoint. Therefore, it is not necessary to provide a 'firmware frameworks' to handle USB device requests in the external master implementation. However, some firmware is needed to handle halt endpoint requests (clear feature/set feature - endpoint type). This should be handled via the SETUP and EP0BUF interrupts. For more information refer section "Endpoint 0" in page 9 / 45 of the attached SX2 datasheet.
Note: SX2 is not recommended for new design