MSP430F2274: Creating a random number generator without the use of time.h.

Sean Kramer

Part Number: MSP430F2274

This question is more based on writing C code and not necessarily on the MSP430 device itself. I wanted to implement a random or pseudo-random number generator that does not involve the use of `srand`, as the `time.h` file takes up more memory than I have available. Is there any specific implementations that I can look to for additional information? Thank you

over 7 years ago

0 Keith Barkley over 7 years ago

Guru 42085 points

Do you want a new seed every time it starts, or the same random seed each time it runs?

0 Sean Kramer over 7 years ago in reply to Keith Barkley

Intellectual 770 points

Are you implying just using `rand()` as a method of creating a random number? If that is the case, then yes, I would want to try and have a new seed each time it runs.

0 Keith Barkley over 7 years ago in reply to Sean Kramer

Guru 42085 points

So you need a form of entropy. What might be different every time your program starts?

0 Sean Kramer over 7 years ago in reply to Keith Barkley

Intellectual 770 points

Ok, I am currently brainstorming what could be used as a source of entropy in the system. Thank you.

0 Keith Barkley over 7 years ago in reply to Sean Kramer

Guru 42085 points

If you don't make too many calls to rand(), you can possible save the seed in non-volatile memory.

0 Sean Kramer over 7 years ago in reply to Keith Barkley

Intellectual 770 points

I was looking into using analog input thermal noise as the seed, but am having trouble understanding how it would be implemented into the device if I am only using a power source from the USB connection.

0 Keith Barkley over 7 years ago in reply to Sean Kramer

Guru 42085 points

The noise from a resistor is 4KTR (i.e., very small). You can just read the noise from one of the analog inputs, but that is not very random. You can put in a reversed biased zener diode, but you will still need to amplify it.

You can also do things like sum up all of ram, but that is not very random, either.

0 Sean Kramer over 7 years ago in reply to Keith Barkley

Intellectual 770 points

Summing up the RAM might not be the best idea as I clear the RAM at the start of the beginning of the program to store a data array. The use of the random number is to find a new location in RAM to move the data array too. Thank you though.

0 Danny F over 7 years ago

Genius 3850 points

"as the `time.h` file takes up more memory than I have available"

S header file, time.h or not, adds precisely zero in memory usage. References to data or functions prototyped on s header file may add memory usage.

If your goal is to seed a peusdo random generator, there are lots of ways to do it. Like adc or phase noise....

If your goal is to generate pesudo random number generator, there are also lots of ways of doing it.

If your goal is to generate truely random numbers, tons of ways, like adc, phase noise, external parts, memory locations, .....

Again, the first step is trying to understand what you are trying to do.

0 Sean Kramer over 7 years ago in reply to Danny F

Intellectual 770 points

A truly random number generator would by goal. And thank you for the clarification, I believe calling `srand(time(0))` is what causes the increased memory usage which exceeds my allowable space.

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MSP430F2274: Creating a random number generator without the use of time.h.