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Line 53... |
* The LFSR-based post-processing can be deactivated using the `lfsr_en_c` constant. The polynomial tap
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* The LFSR-based post-processing can be deactivated using the `lfsr_en_c` constant. The polynomial tap
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mask of the LFSR can be customized using `lfsr_taps_c`.
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mask of the LFSR can be customized using `lfsr_taps_c`.
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**Using the TRNG**
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**Using the TRNG**
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The TRNG features a single register for status and data access. When the _TRNG_CT_EN_ control register bit is
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The TRNG features a single register for status and data access. When the _TRNG_CTRL_EN_ control register (`CTRL`)
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set, the TRNG is enabled and starts operation. As soon as the _TRNG_CT_VALID_ bit is set, the currently
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bit is set, the TRNG is enabled and starts operation. As soon as the _TRNG_CTRL_VALID_ bit is set, the currently
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sampled 8-bit random data byte can be obtained from the lowest 8 bits of the TRNG_CT register
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sampled 8-bit random data byte can be obtained from the lowest 8 bits of the `CTRL` register
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(_TRNG_CT_DATA_MSB_ : _TRNG_CT_DATA_LSB_). The _TRNG_CT_VALID_ bit is automatically cleared
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(_TRNG_CTRL_DATA_MSB_ : _TRNG_CTRL_DATA_LSB_). The _TRNG_CTRL_VALID_ bit is automatically cleared
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when reading the control register.
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when reading the control register.
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[IMPORTANT]
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[IMPORTANT]
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The TRNG needs at least 8 clock cycles to generate a new random byte. During this sampling time
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The TRNG needs at least 8 clock cycles to generate a new random byte. During this sampling time
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the current output random data is kept stable in the output register until a valid sampling of the new byte has
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the current output random data is kept stable in the output register until a valid sampling of the new byte has
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quality is highly effected by the actual configuration of the TRNG and the resulting FPGA mapping/routing.
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quality is highly effected by the actual configuration of the TRNG and the resulting FPGA mapping/routing.
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However, generating larger histograms of the generated random number shows an equal distribution (binary
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However, generating larger histograms of the generated random number shows an equal distribution (binary
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average of the random numbers = 127). A simple evaluation test/demo program can be found in
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average of the random numbers = 127). A simple evaluation test/demo program can be found in
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`sw/example/demo_trng`.
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`sw/example/demo_trng`.
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.TRNG register map
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.TRNG register map (`struct NEORV32_TRNG`)
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[cols="<2,<2,<4,^1,<7"]
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[cols="<2,<2,<4,^1,<7"]
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[options="header",grid="all"]
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[options="header",grid="all"]
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|=======================
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|=======================
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| Address | Name [C] | Bit(s), Name [C] | R/W | Function
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| Address | Name [C] | Bit(s), Name [C] | R/W | Function
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.3+<| `0xffffffb8` .3+<| _TRNG_CT_ <|`7:0` _TRNG_CT_DATA_MSB_ : _TRNG_CT_DATA_MSB_ ^| r/- <| 8-bit random data output
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.3+<| `0xffffffb8` .3+<| `NEORV32_TRNG.CTRL` <|`7:0` _TRNG_CTRL_DATA_MSB_ : _TRNG_CTRL_DATA_MSB_ ^| r/- <| 8-bit random data output
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<|`30` _TRNG_CT_EN_ ^| r/w <| TRNG enable
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<|`30` _TRNG_CTRL_EN_ ^| r/w <| TRNG enable
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<|`31` _TRNG_CT_VALID_ ^| r/- <| random data output is valid when set
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<|`31` _TRNG_CTRL_VALID_ ^| r/- <| random data output is valid when set
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|=======================
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|=======================
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