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Random Number Generator (RNG)
Freescale Semiconductor
25-4
25.2.3
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.
25.2.4
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
Section 25.2.2, “RNG Status Register (RNGSR)
,”
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.
1
LRS
Last read status. Reflects status of most recent read of the FIFO.
0 During last read, FIFO was not empty.
1 During last read, FIFO was empty (underflow condition).
0
SV
Security violation. When enabled by RNGCR[HA], signals that a FIFO underflow has occurred. Bit is sticky and is
only cleared by hardware reset.
0 No violation occurred or RNGCR[HA] is cleared.
1 Security violation (FIFO underflow) has occurred.
: 0xFC0B_4008 (RNGER)
Access: User write-only
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
R
W
ENT
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
Figure 25-3. RNG Entropy Register (RNGER)
: 0xFC0B_400C (RNGOUT)
Access: User read-only
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
R
Random Output
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
Figure 25-4. RNGOUT
Table 25-3. RNGSR Field Descriptions (continued)
Field
Description
Summary of Contents for MCF54455
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Page 145: ...Enhanced Multiply Accumulate Unit EMAC 5 21 Freescale Semiconductor ...
Page 173: ...Cache 6 28 Freescale Semiconductor ...
Page 179: ...Static RAM SRAM 7 6 Freescale Semiconductor ...
Page 207: ...Power Management 9 16 Freescale Semiconductor ...
Page 323: ...Reset Controller Module 13 8 Freescale Semiconductor ...
Page 389: ...Pin Multiplexing and Control 16 44 Freescale Semiconductor ...
Page 575: ...PCI Bus Controller 22 58 Freescale Semiconductor ...
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