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Re: [Discuss-gnuradio] Scrambler Mask, Seed and Lenght

From: Thanasis Balafoutis
Subject: Re: [Discuss-gnuradio] Scrambler Mask, Seed and Lenght
Date: Fri, 15 May 2015 16:19:45 +0300

ok until 3.8 how can I use this block without making mistakes?

If for example want the following polynomials (copy from [1])

                   x^4 + x^3 + x^0 = 0x19
                   x^5 + x^3 + x^0 = 0x29
                   x^6 + x^5 + x^0 = 0x61

do I have to set the length to 5,6,7 respectively?

[1] https://github.com/gnuradio/gnuradio/blob/master/gr-digital/include/gnuradio/digital/lfsr.h#L50-L52

2015-05-15 15:28 GMT+03:00 Johnathan Corgan <address@hidden>:

On Fri, May 15, 2015 at 1:32 AM, Marcus Müller <address@hidden> wrote:
So, yes, I think I agree, and length should at least be 8 here (your polynomial has degree 7), and it's a bit uncommon to see a LFSR being used without the x^0 coefficient. 

Agree.  This was a poor implementation decision by someone who clearly didn't know what he was doing at the time :-)

I've been wanting to fix this for a long time; looks like 3.8 would be a good chance to break this properly.

Johnathan Corgan
Corgan Labs - SDR Training and Development Services

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