A clock-jitter based random number generator using an STM32F100C8 microcontroller and its internal clock sources.
With the RTC being clocked off of the low-speed internal oscillator (LSI), the RTC pre-scaler overflow interrupt was used to periodically sample the SysClk counter that was driven off of the HCLK (derived from separate high-speed internal oscillator (HSI)).
Samples were run through Ilja Gerhardt's NIST testsuite in Python with good results: http://gerhardt.ch/random.php
While this can potentially be used as a building block for protocols which require a cryptographic nonce, do not use this for secure applications without conducting your own independent testing.
CodeSourcery ARM tool chain STM32 Standard Peripheral Library
Initialization code was largely based on Pandafruits excellent STM32 primer: http://pandafruits.com/stm32_primer/stm32_primer_minimal.php