Random Number Generator (Rng); Rng Introduction; Rng Main Features; Rng Functional Description - ST STM32F40 Series Reference Manual

RM0090
21

Random number generator (RNG)

This section applies to the whole STM32F4xx family devices, unless otherwise specified.
21.1

RNG introduction

The RNG processor is a random number generator, based on a continuous analog noise,
that provides a random 32-bit value to the host when read.
The RNG passed the FIPS PUB 140-2 (2001 October 10) tests with a success ratio of 99%.
21.2

RNG main features

●
It delivers 32-bit random numbers, produced by an analog generator
●
40 periods of the PLL48CLK clock signal between two consecutive random numbers
●
Monitoring of the RNG entropy to flag abnormal behavior (generation of stable values,
or of a stable sequence of values)
●
It can be disabled to reduce power-consumption
21.3

RNG functional description

Figure 217

Figure 217. Block diagram

The random number generator implements an analog circuit. This circuit generates seeds
that feed a linear feedback shift register (RNG_LFSR) in order to produce 32-bit random
numbers.
The analog circuit is made of several ring oscillators whose outputs are XORed to generate
the seeds. The RNG_LFSR is clocked by a dedicated clock (PLL48CLK) at a constant
frequency, so that the quality of the random number is independent of the HCLK frequency.
shows the RNG block diagram.
Control register
RNG _CR
RNG_CLK
Status register
RNG _SR
Doc ID 018909 Rev 4
Random number generator (RNG)
32-bit AHB bus
Clock checker &
fault detector
Analog seed
data register
RNG_DR
LFSR
feed a Linear Feedback
Shift Register
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