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Re: [Discuss-gnuradio] gr-ais: bit unstuffing bug?


From: Christian Gagneraud
Subject: Re: [Discuss-gnuradio] gr-ais: bit unstuffing bug?
Date: Fri, 10 Aug 2012 20:30:31 +0100
User-agent: Mozilla/5.0 (X11; Linux i686; rv:14.0) Gecko/20120713 Thunderbird/14.0

On 10/08/12 19:55, Nick Foster wrote:
You can do it either way since unstuffing will never generate a valid
HDLC framing code ("01111110"). Unstuffing before the deframing

For what i understand, bit stuffing never generates framing code (that's the whole point), but the bit *un*stuffing can and will if the payload contains itself a byte which as the same value as the framing code.

Actually, while dumping data from ais_parse.cc, I found that gr-ais unstuffing code do generate framing codes. that has fooled get_tags_in_range (a stop was found because the AIS payload had a 01111110 in it).
Well, I think I found, I'm still scratching my head....

correlators means my tags' sample numbers don't have to be modified for
the bits inserted by the unstuffing operation.

Yes, I see the point. But you could unstuff inline, in place of the memcpy, just before calling parse().

Chris


--n

On Fri, Aug 10, 2012 at 11:47 AM, Christian Gagneraud
<address@hidden <mailto:address@hidden>> wrote:

    Hi all, Nick,

    In gr-ais. the bit un-stuffing is done before the de-framing,
    shouldn't it be done after instead?


    Chris

    --
    Christian Gagneraud,
    Embedded systems engineer.
    Techworks Marine
    1 Harbour road
    Dun Laoghaire
    Co. Dublin
    Ireland
    Tel: + 353 (0) 1 236 5990 <tel:%2B%20353%20%280%29%201%20236%205990>
    Web: http://www.techworks.ie/

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--
Christian Gagneraud,
Embedded systems engineer.
Techworks Marine
1 Harbour road
Dun Laoghaire
Co. Dublin
Ireland
Tel: + 353 (0) 1 236 5990
Web: http://www.techworks.ie/



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