Does the SPI library use the internal USART? I was reading the detailed datasheet for the ATmega328p and noticed that it has an option to use the built-in USART to drive the SPI interface. I just wondered if the arduino SPI library makes use of this? I suspect unlikely because I suppose that the USART is used by the USB on a arduino.
I had a look at the source code for the SPI library. As suspected, it does not use the internal ATMega328 USART. This is useful to know because it means that the USART remains potentially available for other uses in any sketch that is using SPI. I suppose that it also makes the SPI library more portable because perhaps not all arduinen microcontrollers have a built-in USART