Re: Verify the CRC h and CRC from ETI file

[Pascal Charest]

Tu Duong Anh wrote:
> Hi everybody,
>
> I am trying to understand the structure of the ETI file, which I
> generated from the DAB+ Audio WAPP.
>
> In ETS 300 799 (Annex D, p. 52) it is said that the ETI file uses
> CRC16-CCITT to create the fields for the CRC_h and CRC. The register
> is initialized to all ones, therefore CRC16-CCITT (0xFFFF) is used.

Sorry, it is not said so in the document. The polynomial is the same,
but the output is XORed and the state machine configuration is not the same.

> I have used LabVIEW to open the ETI file, to extract all the single
> fields and informations. But my CRC16-CCITT calculation of the CRC_h
> and CRC does not match with the values inside the ETI file. I have
> done the CRC calculation with a LabVIEW application, but also with the
> online calculator
> from http://www.lammertbies.nl/comm/info/crc-calculation.html. Both
> calculators give me the same output on the same input, so they there
> can't be a problem with the CRC calculation implementation.
>
> I am also sure that I am using the right fields (bytes) to calculate
> those CRC.
>
> For CRC_h I have used the contents of the Frame Characterization (FC,
> 4 Bytes), Stream Characterization (STC, number of streams x 4 Bytes,
> two streams are inside the ETI file -> 8 Bytes total) and the
> Multiplex Network Signaling Channel field (MNSC, 2 Bytes). The CRC_h
> of my ETI file is 1110 1001 1010 1011.
>
> For the CRC calculation I haves used as said in the ETS 300 799 the
> content of Main Stream Data (MST, in my file 408 Bytes). My CRC
> calculation should give me as a result the CRC of 1000 1101 1110 1100.
> Just like the CRC_h, the CRC calculation with LabVIEW and the online
> CRC calculator does not match with the CRC values inside the ETI file.

If you try to change the CRC in the ETI file, modulators and receivers
will stop accepting the bitstream because they will detect errors. If
you follow exactly the CRC calculation as defined in 300 799, you will
get the same value as in ETI files. Clue: it is _not_ CCITT.

Regards,

Pascal