|
Message
From: "kw@nie" <kwanie@p...>
Date: Thu, 21 Feb 2002 09:53:28 +0800
Subject: Re: [usb] crc algorithm
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@y...>
To: <usb@o...>
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@p...> 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@o...
> > [mailto:owner-usb@o...] On Behalf
> > Of kebloo@m...
> > Sent: 21 February 2002 08:34
> > To: usb@o...
> > 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
> >
> >
>
> > ATTACHMENT part 2 image/jpeg name=crc5.JPG
>
>
|
 |
Browse
