Gr-ais: bit unstuffing bug?

GNU Radio
1

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

2

You can do it either way since unstuffing will never generate a valid
HDLC
framing code (“01111110”). Unstuffing before the deframing correlators
means my tags’ sample numbers don’t have to be modified for the bits
inserted by the unstuffing operation.

–n

3

On 10/08/12 19:55, Nick F. 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 unstuffing 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

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

4

Hmm, you might be right about that. I’ll take another look.

–n