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Re: Another STM32F103 clone?

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David Brown <david.brown@hesbynett.no> wrote:
> On 17/01/2023 06:07, Rick C wrote:
> 
> > Maybe I didn't read the thread well enough, but I thought this was
> > just a way to generate addresses to test RAM, no?  The only specific
> > property I've seen is that it be "relatively prime" to the memory
> > address space.  LFSR certainly can manage that.  Heck, a Grey code
> > can probably manage that.
> > 
> > With 17 bits, I can generate a PR sequence that is relatively prime
> > to powers of 2 and of length 82,677.
> > 
> > Am I missing something important?
> > 
> 
> Not really, no.  Well, there's the detail that the sequence must be wide 
> enough so that it does not repeat during the testing.  A sequence with 
> length 82,677 will be fine for 128 kB flash (two bytes per element), but 
> is not scalable to a 256 kB flash test.
> 
> But while LFSR's are nice in some use-cases, they are not the simplest 
> sequence generator for software for this sort of thing.
> 
> One of the best is:
> 
>        const uint32_t a = 984830993;
>        const uint32_t b = 1267261529;
> 
>        uint32_t pseudo(uint32_t i) {
>                return (a * i) + b;
>        }
> 
> "a" and "b" are just big prime numbers, as found from this link or by 
> googling around a bit:
> 
> <http://compoasso.free.fr/primelistweb/page/prime/liste_online_en.php>
> 
> 
> This gives you a sequence that is deterministic, you can jump into it at 
> any point, it has no correlation with bit numbers, addresses, etc., and 
> is extremely simple to calculate.

That is more or less one of lousy generators that I used (I had
different constants).   For memory testing it shares the same
problems that counters have: low order bits have short period
that is power of 2.  When you want good randomness, they fail
relatively simple statistical tests.  One can improve them
or they may be good enough for some applications, but one
should be aware of their limitations.

-- 
                              Waldek Hebisch

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Another STM32F103 clone? antispam@math.uni.wroc.pl - 2023-01-08 03:30 +0000
  Re: Another STM32F103 clone? Paul Rubin <no.email@nospam.invalid> - 2023-01-08 11:38 -0800
    Re: Another STM32F103 clone? antispam@math.uni.wroc.pl - 2023-01-09 03:06 +0000
  Re: Another STM32F103 clone? antispam@math.uni.wroc.pl - 2023-01-09 23:23 +0000
    Re: Another STM32F103 clone? Don Y <blockedofcourse@foo.invalid> - 2023-01-09 17:38 -0700
      Re: Another STM32F103 clone? antispam@math.uni.wroc.pl - 2023-01-13 02:28 +0000
        Re: Another STM32F103 clone? Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-15 20:09 -0800
          Re: Another STM32F103 clone? antispam@math.uni.wroc.pl - 2023-01-17 00:43 +0000
            Re: Another STM32F103 clone? Don Y <blockedofcourse@foo.invalid> - 2023-01-16 19:39 -0700
              Re: Another STM32F103 clone? Don Y <blockedofcourse@foo.invalid> - 2023-01-16 19:44 -0700
            Re: Another STM32F103 clone? Rick C <gnuarm.deletethisbit@gmail.com> - 2023-01-16 21:07 -0800
              Re: Another STM32F103 clone? antispam@math.uni.wroc.pl - 2023-01-17 06:04 +0000
                Re: Another STM32F103 clone? Don Y <blockedofcourse@foo.invalid> - 2023-01-17 00:10 -0700
              Re: Another STM32F103 clone? David Brown <david.brown@hesbynett.no> - 2023-01-17 13:48 +0100
                Re: Another STM32F103 clone? antispam@math.uni.wroc.pl - 2023-01-17 17:05 +0000
                Re: Another STM32F103 clone? David Brown <david.brown@hesbynett.no> - 2023-01-17 19:42 +0100
            Re: Another STM32F103 clone? Paul Rubin <no.email@nospam.invalid> - 2023-01-17 11:07 -0800
        Re: Another STM32F103 clone? Don Y <blockedofcourse@foo.invalid> - 2023-01-15 23:47 -0700
          Re: Another STM32F103 clone? antispam@math.uni.wroc.pl - 2023-01-17 05:41 +0000
            Re: Another STM32F103 clone? Don Y <blockedofcourse@foo.invalid> - 2023-01-17 00:04 -0700

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