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Re: [Discuss-gnuradio] udp source - endianness anomaly?

From: David I. Emery
Subject: Re: [Discuss-gnuradio] udp source - endianness anomaly?
Date: Sun, 11 Oct 2009 18:24:38 -0400
User-agent: Mutt/1.4.1i

On Mon, Oct 12, 2009 at 11:16:11AM +1300, Richard Clarke wrote:
> Hi All,
> I was wondering if anyone has had any issues with the interpretation of
> shorts by the GNU Radio udp source function, when the shorts are
> transmitted  from a big endian based platform? In my situation I am
> transmitting UDP packets comprised of 16 bit samples from an AVR32 (big
> endian) which utilises the LWIP open source TCP/IP stack. On my GNU Radio
> destination PC (Intel Pentium D CPU, little endian) I construct a simple
> flowgraph (using GRC/GNU Radio v3.2.1) with a UDP source set to interpret
> incoming data as shorts, into the short to float block and then straight
> into the GUI scope. I'm receiving the UDP packets OK which I assume means
> that all the protocol header info is being interpreted with the correct
> endianness, but the waveform displayed in the scope is corrupt, until that
> is, I manually re-order the LSB and MSB of the transmitted samples at the
> AVR32 end. Normally the lower level network code would take care of byte
> reordering as required to match network byte order to the relevant host byte
> order, however this doesn't appear to be happening correctly on the GNU
> Radio side. I must be missing something simple here, can anyone shed some
> light?

        Is there a good reason to have packets in something other than
network byte order (to match the IP headers) ?

  Dave Emery N1PRE/AE, address@hidden  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."

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