Yahya Tawil wrote a tutorial about flashing EFM32 MCUs with OpenOCD using FT2232H adapter:
Learn how to make flashing your ARM-based MCU easy by using OpenOCD debugger with an FT2232H adapter.
Old MCUs from vendors like ATMEL and MICROCHIP, like the PIC16F and Atmega family, tend to have a special programming interface to program internal flash. For example, Atmega used SPI pins (MISO, MOSI, SCK) and PIC used two pins (PGC, PGD)— one as a clock and another as a bi-directional data line.
New MCUs, especially with an ARM core, use JTAG/SWD as a programming/debugging interface.
Full details at All About Circuits homepage.