STMicroelectronics STM32WL5 Series Reference Manual page 635

RM0453
Conditioning
The conditioning component in the RNG is a deterministic function that increases the
entropy rate of the resulting fixed-length bitstrings output (128-bit). The NIST SP800-90B
target is full entropy on the output (128-bit).
The times required between two random number generations, and between the RNG
initialization and availability of first sample are described in
time.
Output buffer
A data output buffer can store up to four 32-bit words that have been output from the
conditioning component. When four words have been read from the output FIFO through
the RNG_DR register, the content of the 128-bit conditioning output register is pushed into
the output FIFO, and a new conditioning round is automatically started. Four new words are
added to the conditioning output register after a number of clock cycles specified in
Section 22.5: RNG processing
Whenever a random number is available through the RNG_DR register, the DRDY flag
changes from 0 to 1. This flag remains high until the output buffer becomes empty after
reading four words from the RNG_DR register.
Note: When interrupts are enabled an interrupt is generated when this data ready flag transitions
from 0 to 1. Interrupt is then cleared automatically by the RNG as explained above.
True random number generator (RNG)
time.
RM0453 Rev 5
Section 22.5: RNG processing
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