FYI. In the embedded space, peripherals refer to the chip's built in capabilities. Typically there is a peripheral that handles SPI, a peripheral that handles I2C, a peripheral that handles USART. There might be a peripheral that handles USB, or I2S, or any number of different abilities. It's either transistors or microcode on more sophisticated MCUs that allows these peripherals, and not every pin is connected to every peripheral, which can make chip selection even trickier. It really sucks to start designing around a chip that looks like it does everything you need with enough pins to only find out that once you start doing pin layouts you can't use both USART2 and I2C because they use the same pins. Worse, is when the datasheet makes this difficult to discern, and you only find out when doing some firmware work on a devboard.