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Date:	Thu, 26 Mar 2009 10:35:48 +0100
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Subject:	Re: Problems when moving Ubuntu -> Cygwin
From:	Mikael Normark <normark DOT mikael AT gmail DOT com>
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Endianness seemed a bit unlikely to begin with and after checking the
first three values (type, pkg_nr, nr_samples) I found that they were
the same, and correct, on both systems so endianness is not the
problem.
I checked the size of int and long long on both systems and found that
they were the same but when I checked sizeof(struct sample_pkt_t) it
returned 396 on Ubuntu and 528 on Cygwin so I need to find a
workaround for the adressing issue, perhaps that solves the problem.


2009/3/26 Mikael Normark <normark DOT mikael AT gmail DOT com>:
> Hi,
> I have an application which reads data from TCP/IP packets and writes
> it to a file. The program works fine on Ubuntu but now I need it to
> run on my laptop (Vista) so I built it in Cygwin (without problems).
>
> The packet data is read into a struct:
>
> -------------------------------------------------------------------------=
-------
> // Holdning the raw sample data and timestamp when
> // the sample was fetched.
> struct sample_t{
> =A0 =A0int sample;
> =A0 =A0long long timestamp;
> };
>
> // A package that will hold samples data over
> // the TCP transfer.
> struct sample_pkg_t{
> =A0 =A0unsigned int type; =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0//Should always be PKG_SAMPLES
> =A0 =A0unsigned int pkg_nr; =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0//Counter increased for each package
> =A0 =A0unsigned int nr_samples; =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 =A0 =A0 =A0 // Shouldbe same as ADC_SAMPLES_IN_PKG
> =A0 =A0struct sample_t sample[SAMPLES_IN_PKG]; // The samples data
> };
> -------------------------------------------------------------------------=
-------
>
> And the code where the data is written looks like this:
>
> for(si =3D 0; si < sample_pkg->nr_samples; si++){
> =A0 =A0 =A0 timestamp =3D sample_pkg->sample[si].timestamp;
>
> =A0 =A0 =A0 unsigned int secs =3D (timestamp>>32);
> =A0 =A0 =A0 long long nsecs =3D ((timestamp>>17 & 0x7FFF) * 1000000000)/3=
277; //32768
>
> =A0 =A0 =A0 // Save as a line with format (channel <tab> timestamp <tab> =
sample)
> =A0 =A0 =A0 // timestamp is NTP format e.g. seconds since 1 Jan 1900
> =A0 =A0 =A0 sprintf(buf, "%d\t%u%010llu\t%d\n", i, secs, nsecs,
> sample_pkg->sample[si].sample);
> =A0 =A0 =A0 fwrite (buf , 1 , strlen(buf) , pFile );
> }
>
> The program works fine on Ubuntu but when I run it in Cygwin (yes,
> built in Cygwin from source ;) the secs and nsecs values make no sense
> whatsoever. Typical Ubuntu output:
>
> 0 =A0 =A0 =A0 34451499217497700000 =A0 =A024215
> 0 =A0 =A0 =A0 34451499217689300000 =A0 =A023418
> 0 =A0 =A0 =A0 34451499217908100000 =A0 =A023022
> 0 =A0 =A0 =A0 34451499218099400000 =A0 =A022887
> 0 =A0 =A0 =A0 34451499218291100000 =A0 =A023083
> 0 =A0 =A0 =A0 34451499218482400000 =A0 =A023956
> 0 =A0 =A0 =A0 34451499218701200000 =A0 =A022929
> 0 =A0 =A0 =A0 34451499218892500000 =A0 =A023706
>
> Typical Cygwin output:
>
> 0 =A0 =A0 =A0 20601241600000000000 =A0 =A01883963392
> 0 =A0 =A0 =A0 14987793713 =A0 =A0 1
> 0 =A0 =A0 =A0 256220000000000 25221
> 0 =A0 =A0 =A0 24007802880000000000 =A0 =A0-1976369152
> 0 =A0 =A0 =A0 15780897162 =A0 =A0 1
> 0 =A0 =A0 =A0 257650000000000 23954
> 0 =A0 =A0 =A0 27414364160000000000 =A0 =A0-1635713024
> 0 =A0 =A0 =A0 16574000610 =A0 =A0 1
> 0 =A0 =A0 =A0 250970000000000 24616
>
> First thing that came to my mind was endianness, after doing a simple
> test I determined that both computers are little endian as expected.
> As the data in the IP packet is big endian (right?) I wonder if there
> is any difference between Ubuntu/Cygwin in how (or IF) they handle the
> transition before the data reaches the application?
>
> Any input on what the problem could be, or on how to determine what
> the problem is, is greatly appreciated.
>
> Best Regards,
> Mikael Normark
>

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