Embedded boot loader
The embedded boot loader is located in the System memory, programmed by ST during production. It is used to reprogram the Flash memory using one of the following serial interfaces:
USART on pins PA14/PA15 or PA9/PA10
I2C on pins PB6/PB7 ( STM32F070xx and STM32F030xC devices only)
USB DFU interface (STM32F070xx devices only)