Re: [usb] crc algorithm

[Bo <bo_ye@yahoo.com>]

Does anybody know what value we should
prefill for this CRC calculating?
For example, ATM 32-bit CRC should prefill
all 1's, but some HDLC, Ethernet stuff need
to prefill all 0's.
What's the reason for doing that?
Is it true Single String Feed Back need to 
prefill 0's?

regards
bo


--- Madhusudhan Rao <madhu_sudhana_rao@yahoo.com>
wrote:
> HiTambunan,
>    G(x) = x^16+x^15+x^2+1 for  1000000000000101B.
>    G(x) = x^5+x^2+1 for  00101B.
> X^5 in the above expression will give u information
> as
> you are using 5 bit crc. otherwise we will not have
> any idea that how much crc polynomial length.
> I hope the above explanation is clear to u.
> If u still not clear i will send u an example code
> for
> crc aslo.
> 
> Best regards
> Madhu
> 
> --- kebloo@mitra.net.id wrote:
> > Hello,
> > 
> > Sorry for this beginner question, but I wish some
> > one could
> > answer my curiosity...
> > 
> > USB 1.1 specification defines generator polynomial
> > of 5-bit crc 
> > as G(x) = x^5+x^2+1 and binary pattern that
> > represent it as
> > 00101B and 16-bit crc as G(x) = x^16+x^15+x^2+1
> and
> > binary pattern that represent it as
> > 1000000000000101B.
> > My question is why the binary pattern stated like
> > that and
> > not 100101B for 5-bit crc and 11000000000000101B ?
> > Thanks....
> > 
> > 
> > 
> > Best Regard,
> > 
> > 
> > RE Tambunan
> > --
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> 
> 
> =====
> MadhusudhanaRao.M
> 
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