It can be argued that SRAM is not designed to produce random numbers. For additional safety, two other hardware sources are added:
the microcontroller’s built-in True Random Number Generator (TRNG) module, and
measurements of a floating input to the Analogue to Digital Converter (ADC).
The sources are mixed in such a way that in the unlikely case of a backdoor in the TRNG module, the security of Mycelium Entropy is not reduced.