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<<<
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==== True Random-Number Generator (TRNG)
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==== True Random-Number Generator (TRNG)
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[cols="<3,<3,<4"]
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[frame="topbot",grid="none"]
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[frame="topbot",grid="none"]
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|=======================
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|=======================
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| Hardware source file(s): | neorv32_trng.vhd |
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| Hardware source file(s): | neorv32_trng.vhd |
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| Software driver file(s): | neorv32_trng.c |
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| Software driver file(s): | neorv32_trng.c |
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| | neorv32_trng.h |
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| | neorv32_trng.h |
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| Top entity port: | none |
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| Top entity port: | none |
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| Configuration generics: | _IO_TRNG_EN_ | implement TRNG when _true_
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| Configuration generics: | _IO_TRNG_EN_ | implement TRNG when _true_
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| CPU interrupts: | none |
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| CPU interrupts: | none |
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|=======================
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|=======================
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**Theory of Operation**
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**Theory of Operation**
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The NEORV32 true random number generator provides _physical_ true random numbers.
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The NEORV32 true random number generator provides _physical_ true random numbers.
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Instead of using a pseudo RNG like a LFSR, the TRNG uses a simple, straight-forward ring
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Instead of using a pseudo RNG like a LFSR, the TRNG uses a simple, straight-forward ring
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oscillator concept as physical entropy source. Hence, voltage, thermal and also semiconductor manufacturing
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oscillator concept as physical entropy source. Hence, voltage, thermal and also semiconductor manufacturing
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fluctuations are used to provide a true physical entropy source.
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fluctuations are used to provide a true physical entropy source.
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The TRNG is based on the _neoTRNG_, which is a "spin-off project" of the
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The TRNG is based on the _neoTRNG_, which is a "spin-off project" of the
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NEORV32 processor. The TRNG uses the default neoTRNG configuration, which showed very good results in the
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NEORV32 processor. The TRNG uses the default neoTRNG configuration, which showed very good results in the
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`dieharder` battery of random number tests. More detailed information about the neoTRNG, it's architecture and a
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`dieharder` battery of random number tests. More detailed information about the neoTRNG, it's architecture and a
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detailed evaluation of the random number quality can be found it it's repository: https://github.com/stnolting/neoTRNG
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detailed evaluation of the random number quality can be found it it's repository: https://github.com/stnolting/neoTRNG
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.Platform Independent Architecture
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[NOTE]
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[NOTE]
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The TRNG features a platform independent architecture without FPGA-specific primitives, macros or
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The TRNG features a platform independent architecture without FPGA-specific primitives, macros or
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attributes so it can be synthesized for _any_ FPGA.
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attributes so it can be synthesized for _any_ FPGA.
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.Inferring Latches
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[NOTE]
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The synthesis tool might emit a warning like _"inferring latches for ... neorv32_trng ..."_. This is no problem
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as this is what we actually want (the TRNG is based on latches).
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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_CTRL_EN_ control register (`CTRL`)
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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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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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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 `CTRL` 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_CTRL_DATA_MSB_ : _TRNG_CTRL_DATA_LSB_). These bits always keep the latest valid data obtained from the TRNG
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(_TRNG_CTRL_DATA_MSB_ : _TRNG_CTRL_DATA_LSB_). These bits always keep the latest valid data obtained from the TRNG
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entropy source. The _TRNG_CTRL_VALID_ bit is automatically cleared when reading the control register.
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entropy source. The _TRNG_CTRL_VALID_ bit is automatically cleared when reading the control register.
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.TRNG Reset
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[NOTE]
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[NOTE]
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The TRNG core does not provide a dedicated reset. In order to ensure correct operations, the TRNG should be
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The TRNG core does not provide a dedicated reset. In order to ensure correct operations, the TRNG should be
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disabled (=reset) by clearing the _TRNG_CTRL_EN_ and waiting some milliseconds before re-enabling it.
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disabled (=reset) by clearing the _TRNG_CTRL_EN_ and waiting some milliseconds before re-enabling it.
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.TRNG register map (`struct NEORV32_TRNG`)
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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+<| `NEORV32_TRNG.CTRL` <|`7:0` _TRNG_CTRL_DATA_MSB_ : _TRNG_CTRL_DATA_MSB_ ^| r/- <| 8-bit random data
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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
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<|`30` _TRNG_CTRL_EN_ ^| r/w <| TRNG enable
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<|`30` _TRNG_CTRL_EN_ ^| r/w <| TRNG enable
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<|`31` _TRNG_CTRL_VALID_ ^| r/- <| random data is valid when set
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<|`31` _TRNG_CTRL_VALID_ ^| r/- <| random data is valid when set
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|=======================
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|=======================
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