* Raptor Engineering litespi, improved <https://gitlab.raptorengineering.com/kestrel-collaboration/kestrel-litex/litespi>
* <https://gitlab.raptorengineering.com/raptor-engineering-public/lpc-spi-bridge-fpga/-/blob/master/spi_master.v>
* Also Shakti E-Class peripheral set in BSV
+* <https://github.com/freecores/tiny_spi/blob/master/driver/linux-2.6/oc_tiny_spi.c>