
DocID024597 Rev 5
813/1830
RM0351
True Random Number Generator (RNG)
816
The user can enable or disable the above interrupt sources individually by changing the
mask bits or the general interrupt control bit IE in the RNG_CR register. The status of the
individual interrupt sources can be read from the RNG_SR register.
Note:
Interrupts are generated only when RNG is enabled.
27.6
RNG processing time
The RNG can produce one 32-bit random numbers every 42 RNG clock cycles.
After enabling or re-enabling the RNG using the RNGEN bit it takes 46 RNG clock cycles
before random data are available.
27.7
Entropy source validation
27.7.1 Introduction
In order to assess of the amount of entropy available from the RNG, STMicroelectronics has
tested the RNG against AIS-31 PTG.2 set of tests. The results can be provided on demand
or the customer can reproduce the measurements using the AIS reference software. The
customer could also test the RNG against an older NIST SP800-22 set of tests.
27.7.2 Validation
conditions
STMicroelectronics has validated the RNG true random number generator in the following
conditions:
•
RNG clock rng_clk= 48 MHz
•
AHB clock rng_hclk= 60 MHz
27.7.3 Data
collection
If raw data needs to be read instead of pre-processed data the developer is invited to
contact STMicroelectronics to receive the correct procedure to follow.
Table 173. RNG interrupt requests
Interrupt event
Event flag
Enable control bit
Data ready flag
DRDY
IE
Seed error flag
SEIS
IE
Clock error flag
CEIS
IE