Re: [usb] crc algorithm

[Bo <bo_ye@yahoo.com>]

Hi Tambunan,
    For my understanding, it really doesn't
matter what pattern you should fill during the
initialization. As far as you use the same
pattern on both encode and decode part, it should
come out the same result. You can check it use
math calculation, C or even verilog.
    I don't think it is use for protecting 
leading 0's in the packet, since you can always
turn on/off the CRC calculation. 
Like token CRC, it only cover device/endpoint 
address and frame number. 
Data CRC, it only cover Data field.


regards
bo



--- RE Tambunan <kebloo@mitra.net.id> wrote:
> On 20 Feb 2002 at 11:32, Bo wrote:
> 
> > 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?
> For USB, register value is filled with 1s before CRC
> calculation.
> It is stated in USB 1.1 & USB 2.0 specification
> section 8.3.5
> at 2nd paragraph. The reason is to protect also
> leading 0s
> in front of a packet. This is the reason stated in
> the " CRC
> in USB" whitepaper.
> 
> What I don't know is about the binary bit
> representation of
> Generator Polynomial. Could you help me with that
> information? Or another on-line reference maybe?
> 
> > 
> > regards
> > bo
> > 
> Best Regard,
> 
> 
> RE Tambunan
> --
> To unsubscribe from usb mailing list please visit http://www.opencores.org/mailinglists.shtml

__________________________________________________
Do You Yahoo!?
Yahoo! Sports - Coverage of the 2002 Olympic Games
http://sports.yahoo.com
--
To unsubscribe from usb mailing list please visit http://www.opencores.org/mailinglists.shtml