Wireshark mailing list archives
Re: Calculating CRC5 of 11-bit data
From: Tomasz Moń <desowin () gmail com>
Date: Sat, 20 Jul 2019 05:37:40 +0200
On Sat, Jul 20, 2019 at 2:35 AM Guy Harris <guy () alum mit edu> wrote:
On Jul 19, 2019, at 9:26 AM, Tomasz Moń <desowin () gmail com> wrote:1. Compute the CRC5 bitwise on the 11 bits of data, or 2. Compute the CRC5 with table-based algorithm on 2 bytes (11 bits data + 5 bits CRC) and relying on the CRC properties expect fixed output.Meaning that if you run the CRC on the entire Link Control Word, including the 5-bit CRC and the remaining 11 bits, the result should be a fixed value? (Is that what "The residual of CRC-5 shall be 01100b." is referring to?)
Yes, the CRC residue is what you should get after computing CRC over the message *and* its message's CRC. In case of CRC-5/USB the residual is decimal 6 (which matches the value 01100b from your quote if it is lsb first).
If the goal is just to check the CRC, approach 2) seems as if it's as good as approach 1), and may involve a simpler implementation.
The advantage of 1) over 2) is the ability to be able, if the CRC is incorrect, to tell what the correct CRC should have been. Approach 2) allows only to veify if the CRC is correct - but at the advantage of being able to take full bytes as input. ___________________________________________________________________________ Sent via: Wireshark-dev mailing list <wireshark-dev () wireshark org> Archives: https://www.wireshark.org/lists/wireshark-dev Unsubscribe: https://www.wireshark.org/mailman/options/wireshark-dev mailto:wireshark-dev-request () wireshark org?subject=unsubscribe
Current thread:
- Calculating CRC5 of 11-bit data Tomasz Moń (Jul 19)
- Re: Calculating CRC5 of 11-bit data Ross Jacobs (Jul 19)
- Re: Calculating CRC5 of 11-bit data Tomasz Moń (Jul 19)
- Re: Calculating CRC5 of 11-bit data Guy Harris (Jul 19)
- Re: Calculating CRC5 of 11-bit data Tomasz Moń (Jul 19)
- Re: Calculating CRC5 of 11-bit data Tomasz Moń (Jul 20)
- Re: Calculating CRC5 of 11-bit data John Sullivan (Jul 20)
- Re: Calculating CRC5 of 11-bit data Tomasz Moń (Jul 20)
- Re: Calculating CRC5 of 11-bit data John Sullivan (Jul 21)
- Re: Calculating CRC5 of 11-bit data Tomasz Moń (Jul 25)
- Re: Calculating CRC5 of 11-bit data Tomasz Moń (Jul 19)
- Re: Calculating CRC5 of 11-bit data Ross Jacobs (Jul 19)