Recent versions of flashrom support the -p ft2232spi option which allows you to use a FTDI FT2232H/FT4232H based device as external SPI programmer.
- Put a jumper on pins 8 and 9, which configures the device to be powered by USB. Without this jumper it will not be powered, and thus not be detected by your OS (e.g. it will not appeat in the lsusb output).
- TODO: Voltage regulator 3.3V and two capacitors.