Re: [usb] crc algorithm

["kw@nie" <kwanie@pacific.net.sg>]

Bi Bo,

You are right about pre-loading the register with '1's. it's careless of me
to not have included it.

>      The first part, looks like using two-string
> feed back instead. It will result in
> Y = 1 + X^3 + X^5 instead of Y = 1 + X^2 + X^5 in
> USB protocol for token packet checksum.

The result is still Y = 1 + X^3 + X^5 => 2^0 + 2^3 + 2^5, with 2^0 being the
data bit.


----- Original Message -----
From: "Bo" <bo_ye@yahoo.com>
To: <usb@opencores.org>
Sent: Thursday, February 21, 2002 7:33 AM
Subject: RE: [usb] crc algorithm


> Hi Kwanie,
>      Thanks for the diagram.
>      I agree on the second part. Xor the X0 with
> the MSB will yield the correct when the last bit
> is shifted in. But need to preset all the register
> to 1's. (correct me if I am wrong)
>      The first part, looks like using two-string
> feed back instead. It will result in
> Y = 1 + X^3 + X^5 instead of Y = 1 + X^2 + X^5 in
> USB protocol for token packet checksum.
>
> regards
> bo
>
>
> --- "kw@nie" <kwanie@pacific.net.sg> wrote:
> > I think I know why the binary representations, in
> > the USB specification, are
> > different from the polynomials. Attached is a brief
> > explanation based on the
> > 5-bit CRC but the principle applies for both CRC
> > generators.
> >
> > Cheers,
> > kwanie
> >
> >
> >
> >
> >  -----Original Message-----
> > From: owner-usb@opencores.org
> > [mailto:owner-usb@opencores.org]  On Behalf
> > Of kebloo@mitra.net.id
> > Sent: 21 February 2002 08:34
> > To: usb@opencores.org
> > Subject: [usb] crc algorithm
> >
> > 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
> > --
> > To unsubscribe from usb mailing list please visit
> > http://www.opencores.org/mailinglists.shtml
> >
>
> > ATTACHMENT part 2 image/jpeg name=crc5.JPG
>
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