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48.1.3.3.27.2 Function
Various statistical tests are run as a normal part of the TRNG's entropy generation
process. The least-significant 16 bits of the TRNG0_STATUS register reflect the result
of each of these tests. The status of these bits will be valid when the TRNG has finished
its entropy generation process. Software can determine when this occurs by polling the
ENT_VAL bit in the TRNG0 Miscellaneous Control Register.
Note that there is a very small probability that a statistical test will fail even though the
TRNG is operating properly. If this happens the TRNG will automatically retry the entire
entropy generation process, including running all the statistical tests. The value in
RETRY_CT is decremented each time an entropy generation retry occurs. If a statistical
check fails when the retry count is nonzero, a retry is initiated. But if a statistical check
fails when the retry count is zero, an error is generated by the RNG. By default
RETRY_CT is initialized to 1, but software can increase the retry count by writing to the
RTY_CT field in the TRNG0_SCMISC register.
All 0s will be returned if this register address is read while the RNG is in Program Mode
(see PRGM field in TRNG0_MCTL register. If this register is read while the RNG is in
Run Mode the value returned will be formatted as follows.
48.1.3.3.27.3 Diagram
Bits
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
R
Reserved
W
Reset
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Bits
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
R
W
Reset
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
48.1.3.3.27.4 Fields
Field
Function
31-20
—
Reserved. Always 0.
19-16
RETRY_CT
RETRY COUNT. This represents the current number of entropy generation retries left before a statistical
text failure will cause the RNG to generate an error condition.
15
Test Fail, Mono Bit. If TFMB=1, the Mono Bit Test has failed.
Table continues on the next page...
Chapter 48 SA-TRNG Standalone
K32 L2A Reference Manual, Rev. 2, 01/2020
NXP Semiconductors
1247
Summary of Contents for K32 L2A Series
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