| ??? 10/30/09 15:11 Read: times |
#170252 - What interrupt? Responding to: ???'s previous message |
Per said:
If the timer runs at 1MHz it will only have ticked 1000 ticks in 1ms so each interrupt would produce very few bits of random data to add to the entropy pool. What interrupt? My scheme doesn't use interrupts. Also, I wouldn't read out the timer every 1msec. That's way too many read outs per second and the timer cannot run freely enough between subsequent readings. I only wanted to say, that the lower corner frequency of the bandpaß does not allow to read out the timer too early, because then the timer could not have been clocked. The reason, why the timer should not be read out every 1msec, is, that then the numbers 0 to 255 are not equally probable to be be read out. With only 1000 ticks some of them might be more probable than others. Ok, this will average out the next subsequent read outs, but is a slight deviation from the ideal distribution. More, I didn't want to recommend to read out the timer in a periodic way. The time intervals between subsequent read outs must not be equal at all. Don't expect too much from this little circuit. It shows two advantages. After powering on the circuit, the noise generator always starts with a fresh truly random number. Also, each read out of timer gives a truly random number. But if you want an ideal distribution, then you should wait between subsequent read outs, the longer the better. Kai Klaas |
