question regarding random number generator

[Altera_Forum]

hii.. 

 i would like to ask if there is any library that have a function to generate numbers randomly within certain range..???  i wanna make a component that takes an input once add to its value 15 and subtract from it 15 and gives output within this range randomly  i.e --> output= rand[input+15, input-15] i've no problem with the design except of the part of random value generation i did some work arround to do so that i'm not satisfied with.. here is what i did --> xoring 2 bits putting the result in another place..   any idea how can i do this..  all your helps highly appreciated..  thanks, Niveen..

[Altera_Forum]

Questions: 

1. Should this block be synthesisable? 2. How "random" does it need to be?  I ask these questions because: 1. VHDL has a random number generator, but it is not synthesisable and only meant for testbenches 2. Have you looked into a LFSR? http://en.wikipedia.org/wiki/lfs with this you can create a pseudo random sequence. This would be the easiest logic solution. I have heard of others before but they often involve rlocs and require good knowledge on oscilators. One solution (i havent done it, but had it described) is to route a clock though some logic as far apart as possible. Then sample the clock at a given rate, to try and give a random bit (it was described to me a long time ago, so I may have some details wrong).

[Altera_Forum]

--- Quote Start ---  Questions: 1. Should this block be synthesisable?   --- Quote End ---   no just testing    --- Quote Start ---  Questions: 2. How "random" does it need to be?   --- Quote End ---   i want to generate 36 output values with only 1 input    --- Quote Start ---  Questions: I ask these questions because: 1. VHDL has a random number generator, but it is not synthesisable and only meant for testbenches   --- Quote End ---   would plz tell me about it, and if it take range or not??    --- Quote Start ---  Questions: 2. Have you looked into a LFSR? http://en.wikipedia.org/wiki/lfs with this you can create a pseudo random sequence. This would be the easiest logic solution. I have heard of others before but they often involve rlocs and require good knowledge on oscilators. One solution (i havent done it, but had it described) is to route a clock though some logic as far apart as possible. Then sample the clock at a given rate, to try and give a random bit (it was described to me a long time ago, so I may have some details wrong).  --- Quote End ---   the work arround i did was similar to LFSR.. execuse me, i couldn't get the rest of this..    thanks, Niveen

[Altera_Forum]

Per Tricky's comments, if an LFSR is sufficient, there is a tutorial and code here: 

 http://www.ovro.caltech.edu/~dwh/correlator/pdf/lfsr_tutorial.pdf http://www.ovro.caltech.edu/~dwh/correlator/pdf/lfsr_tutorial_src.zip  You would need to decide whether you want uniform or Gaussian(-like) noise, and then just scale it to the numeric range you describe above.  Cheers, Dave

[Altera_Forum]

There's a synthesizable random number generator using an inverter chain in the Altera cookbook: http://www.altera.com/literature/manual/stx_cookbook.pdf 

See chapter 14

[Altera_Forum]

Thanks alot Dave for the tutorial.. :) 

 whenever i try to post any "reply with quote" it dissapear once i click "post".. any idea why does this happen  thanks, Niveen..

[Altera_Forum]

Thanks alot jederrick for the cookbook link.. :)

[Altera_Forum]

--- Quote Start ---   whenever i try to post any "reply with quote" it dissapear once i click "post".. any idea why does this happen   --- Quote End ---    Works fine for me - WinXP + Firefox.  Cheers, Dave