A common way to handle this for non-cryptographic randomness without using any extra hardware is leave a pin floating that has an A/D converter on it and oversa

A common way to handle this for non-cryptographic randomness without using any extra hardware is leave a pin floating that has an A/D converter on it and oversampling it to measure the lowest one or two bits. Feeding in white noise though requires something to generate that white noise. When extra hardware is available you absolutely generate that noise and getting a higher quality and more reliable source of randomness.