The read data FIFO can be accessed through the “rd_mem” bus in Stratix® 10 Serial Flash Mailbox Client Intel® FPGA IP Core. To read data stored in the read data FIFO, you need to read data from the “rd_mem” bus. Refer to the IP rd_mem’s base and end address in the Intel® Quartus® Prime Platform Designer for the start address and list of addresses that you can read into.
For more details about the read operation flow, refer to Stratix® 10 Serial Flash Mailbox Client Intel® FPGA IP Core User Guide.