[Kimio Kosaka] wrote a dual-purpose TPI and ISP firmware for the ATmegaxxUn chips that are used as a USB-serial ... to flash a DFU USB bootloader into the Arduino, then load up the flash ...

So he tried his hand with some really small SMD parts by building this USB to serial Arduino programmer. The chip he went with isn’t the FTDI part we’re used to. Instead of using an FT232RL ...