Verification IP for SPI protocol
http://ee.hawaii.edu/~tep/EE491E/Notes/HC11A8/HC11A8_SPI.pdf
http://web.engr.oregonstate.edu/~traylor/ece473/lectures/spi.pdf
https://www.analog.com/en/analog-dialogue/articles/introduction-to-spi-interface.html
https://wiki.analog.com/_media/resources/technical-guides/adispi_rev_1p0_customer.pdf