mirror of
https://github.com/RobTillaart/Arduino.git
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75 lines
2.5 KiB
Markdown
75 lines
2.5 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/DEVRANDOM/blob/master/LICENSE)
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[](https://github.com/RobTillaart/DEVRANDOM/releases)
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# DEVRANDOM
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Arduino library to wrap a random generator in a stream
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## Description
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The library implements a stream class that mimics the /dev/random
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device of a linux system. It can be used for testing with streams.
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## Interface
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### Constructor
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- **DEVRANDOM()** Constructor
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- **DEVRANDOM(char \* str)** Constructor
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- **DEVRANDOM(uint32_t val)** Constructor
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- **DEVRANDOM(float val)** Constructor
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### Streeam interface
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to read and to reseed the random generator.
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- **available()** There is always 1 next byte available
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- **peek()** will give you next byte
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- **read()** will give you next byte and generate a new one.
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- **write()** data will be used for reseeding the random number generator (RNG)
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(SW mode only, in HW mode and AN mode the seed is used to XOR the value, so it
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does have some effect);
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- **flush()** to keep the CI happy.
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### Random generator selection
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- **useSW()** use a software random number generator. This is the default.
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By default the build-in random number generator is used.
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This can be replaced by a RNG of your choice.
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- **useHW(pin)** use digitalRead to read 8 bits from a defined pin.
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One can build a hardware RNG that flips between 0 and 1 very rapidly and unpredictably.
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Connect this signal to the pin and it will be read and generate a random byte.
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The seed value from the write is used as an XOR byte.
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- **useAR(pin)** use the analogRead to read 8 bits
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This can be fed with an analog noise source.
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The seed value from the write is used as a XOR byte.
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- **getMode()** returns the source of randomness => 0=SW, 1=HW, 2=AR (see above).
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As **write()** reseeds the RNG, printing to **DEVRANDOM** will also reseed the RNG.
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E.g. **dr.println("Hello world");** would reseed it too.
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## Operation
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See example sketches.
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### Example
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As shown in the example one can use fscanf to read larger datatypes,
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```cpp
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DEVRANDOM dr;
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uint32_t x;
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fscanf((FILE*) &dr, "%lu", &x);
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Serial.println(x);
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```
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However float is not supported standard in the fscanf by UNO and strings (%s) generate garbage.
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So a password generator is a bit more difficult (and a good exercise).
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