MSC datagroup parsing improvements #1
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See Annex E in EN 300 401
Previously the offset was used for the minimum header size check but ignored by the rest of the function.
Use transport ID, user access field size and extension bits in header to determine header size. Use CRC presence flag to determine is CRC is present. Do not assume the datagroup transports a MOT segment. This means the datagroup data field size has to be determined using the datagroup's header information only.
magicbadger
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Feb 23, 2017
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Interesting! For some reason I changed the predefined CRC function from crc-16-genibus (which I believe is equivalent) to x25. Not sure why, but I suspect my lack of understanding of Annex E.
magicbadger
approved these changes
Feb 23, 2017
magicbadger
approved these changes
Feb 23, 2017
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Thanks for your attention on this (especially the CRC). |
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This commit seems to break functionality. Recommend a revert to the original and testing. Fails to execute with errors at lines 345 and 357 (reference to self.transport_id, should be self._transport_id). EPG encoded using this version of msc fails to decode. EPG encoded using the prior version does encode properly. |
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While trying to parse captured data from a DAB test service component I found the CRC computed by the existing implementation didn't match the test data I had. I'd like to contribute the changes back so I am opening this PR for discussion.