Excerpt:

"One of my favorite microchips of all time is FT2232H from FTDI — its dual channel USB to serial converter that supports various protocols and configurations. It can work with UART, I2C, SPI and JTAG protocols, it also supports bit-bang mode and multi-protocol synchronous high speed engine (MPSSE) — its pretty much a real digital electronics swiss knife. There’s also a single channel version of this chip called FT232H, but as for me it’s more convenient to have dual channel one: for example, you can flash firmware to your target device over SPI and debug it via JTAG in the same time which is very convenient. Also, there are some motherboards which use more than one SPI flash chip to store platform firmware (my Intel DQ77KB motherboard uses two). To work with this neat chip you can buy official FT2232H Mini Module from FTDI or make your own board."