4 ms·

Could you have a true random number generator that with each clock cycle had a 50% chance of producing a 1 or 0, then XOR that stream with the data stream?

neltnerb 9y ago
How expensive are RNGs to implement? I'm not sure how they work. I think your idea would work though. You might make do with a very long prime value like 4073 that just clocks around endlessly, which will rarely line up meaningfully with anything else. It does seem memory intensive though, maybe these minor issues aren't a big deal in simple enough systems that this could ever work anyway. Maybe you just use 127 bits or something to randomize it, probably more than enough since the goal is likely mostly to avoid aliasing. Even with multiple incoming synchronized sources if you use different mixing patterns it might work out fine.
- seiferteric 9y ago
  Yes I guess true randomness isn't really needed.
- teemwerk 9y ago
  i don't know how truly random a crc function is, but they're really cheap to implement in an fpga. especially if you're just pulling the bit off the end for a bitstream, and you can just feed the output or some polynomial into the input instead of an input stream. but that's where my thoughts end. https://en.wikipedia.org/wiki/Computation_of_cyclic_redundancy_checks https://en.wikipedia.org/wiki/Computation_of_cyclic_redundan...
- pjc50 9y ago
  In physical hardware you can get "real" noise out of a single diode with appropriate processing. https://www.maximintegrated.com/en/app-notes/index.mvp/id/3469 https://www.maximintegrated.com/en/app-notes/index.mvp/id/34... The effect is a true quantum process whereby one electron tunneling across the junction triggers a large number of other electrons into moving.
  - neltnerb 9y ago
    Nice! I see the noise spectra, I am guessing the long tail out at high frequencies means that the recovery time is short enough that subsequent bits aren't correlated?

neltnerb 9y ago

How expensive are RNGs to implement? I'm not sure how they work. I think your idea would work though. You might make do with a very long prime value like 4073 that just clocks around endlessly, which will rarely line up meaningfully with anything else. It does seem memory intensive though, maybe these minor issues aren't a big deal in simple enough systems that this could ever work anyway. Maybe you just use 127 bits or something to randomize it, probably more than enough since the goal is likely mostly to avoid aliasing. Even with multiple incoming synchronized sources if you use different mixing patterns it might work out fine.

seiferteric 9y ago
Yes I guess true randomness isn't really needed.
teemwerk 9y ago
i don't know how truly random a crc function is, but they're really cheap to implement in an fpga. especially if you're just pulling the bit off the end for a bitstream, and you can just feed the output or some polynomial into the input instead of an input stream. but that's where my thoughts end. https://en.wikipedia.org/wiki/Computation_of_cyclic_redundancy_checks https://en.wikipedia.org/wiki/Computation_of_cyclic_redundan...
pjc50 9y ago
In physical hardware you can get "real" noise out of a single diode with appropriate processing. https://www.maximintegrated.com/en/app-notes/index.mvp/id/3469 https://www.maximintegrated.com/en/app-notes/index.mvp/id/34... The effect is a true quantum process whereby one electron tunneling across the junction triggers a large number of other electrons into moving.
- neltnerb 9y ago
  Nice! I see the noise spectra, I am guessing the long tail out at high frequencies means that the recovery time is short enough that subsequent bits aren't correlated?