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Random Number Generator (RNG)
Field
1
Last read status. Reflects status of most recent read of the FIFO.
LRS
0 During last read, FIFO was not empty.
1 During last read, FIFO was empty (underflow condition).
0
Security violation. When enabled by RNGCR[HA], signals that a FIFO underflow has occurred. Bit is sticky and is
SV
only cleared by hardware reset.
0 No violation occurred or RNGCR[HA] is cleared.
1 Security violation (FIFO underflow) has occurred.
34.2.3
RNG Entropy Register (RNGER)
The RNGER is a write-only register which allows the user to insert entropy into the RNG. This register
allows an external user to continually seed the RNG with externally generated random data. Although use
of this register is recommended, it is optional. The RNGER can be written at any time during operation.
Each time the RNGER is written, the value updates the internal state of the RNG. The update is performed
in such a way that the entropy in the RNG's internal state is preserved. Use of the RNGER can increase
the entropy but never decrease it.
Address: 0xEC08_8008 (RNGER)
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
R
W
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
34.2.4
RNG Output FIFO (RNGOUT)
The RNGOUT provides temporary storage for random data generated by the RNG. As long as the FIFO
is not empty, a read of this address returns 32 bits of random data. If the FIFO is read when it is empty,
RNGSR[EI, FUF, LRS] are set. If the interrupt is enabled in RNGCR, an interrupt is triggered to the
interrupt controller. The RNGSR[OFL], described in
can be polled to monitor how many 32-bit words are currently resident in the FIFO. A new random word
pushes into the FIFO every 256 clock cycles (as long as the FIFO is not full). It is very important to poll
RNGSR[OFL] to make sure random values are present before reading from RNGOUT.
Address: 0xEC08_800C (RNGOUT)
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
R
W
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
34-4
Table 34-3. RNGSR Field Descriptions (continued)
Description
Figure 34-3. RNG Entropy Register (RNGER)
Random Output
Figure 34-4. RNGOUT
MCF5329 Reference Manual, Rev 3
9
ENT
Section 34.2.2, "RNG Status Register
9
Access: User write-only
8
7
6
5
4
3
2
1
0
(RNGSR),"
Access: User read-only
8
7
6
5
4
3
2
1
0
Freescale Semiconductor
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