Using Icestick fpga USB channel B for SPI communication

http://blog.julian1.io/2017/01/29/icestick-ftdi-spi.html

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refs

basics, http://www.ftdichip.com/Support/Documents/AppNotes/AN_135_MPSSE_Basics.pdf

op codes, http://www.ftdichip.com/Support/Documents/AppNotes/AN_108_Command_Processor_for_MPSSE_and_MCU_Host_Bus_Emulation_Modes.pdf

spi example, http://www.ftdichip.com/Support/Documents/AppNotes/AN_114_FTDI_Hi_Speed_USB_To_SPI_Example.pdf

data sheet, http://www.ftdichip.com/Support/Documents/DataSheets/ICs/DS_FT2232H.pdf

api https://www.intra2net.com/en/developer/libftdi/documentation/group__libftdi.html

iceprog https://github.com/cliffordwolf/icestorm/blob/master/iceprog/iceprog.c