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Re: [Discuss-gnuradio] floats over UDP into GRC?

From: Mark Cetilia
Subject: Re: [Discuss-gnuradio] floats over UDP into GRC?
Date: Sun, 18 Sep 2011 22:14:28 -0400

Ok so I have made some headway & am now sending floats over UDP as binary data 
(4 bytes),
followed by a null packet (1 byte of "\0") but am not sure how to unpack the 
data into a float in GRC…
It's all happening within the same machine on an Intel Mac so there shouldn't 
be any issues with endianness.
Any ideas / suggestions?


mark.cetilia.org | mem1.com | reduxproject.com

On Sep 13, 2011, at 8:24 PM, Mark Cetilia wrote:

> Thanks so much Marcus, this makes perfect sense…
> Cheers,
> Mark
> --
> mark.cetilia.org | mem1.com | reduxproject.com
> On Sep 13, 2011, at 7:45 PM, Marcus D. Leech wrote:
>>> I'm producing the stream in C++ (using openFrameworks) and sending the data 
>>> as char arrays,
>>> and have confirmed that this is indeed all that is being sent (e.g. "1.25")…
>> So, you're sending them in ASCII?  As ASCII strings?
>> GRC/gnuradio has no method for dealing with that.  The UDP block assumes 
>> native machine-binary format for data coming in
>> over UDP.  Doing it in ASCII (Or Unicode, or whatever) strings will be 
>> hugely inefficient, both in terms of bandwidth required--
>> it takes many more bytes to represent a floating-point number in ASCII, than 
>> in the native binary format, and converting from
>> strings back into the native binary format is also quite expensive.  Since 
>> UDP is entirely binary transparent, there's no reason
>> to send them as ascii strings.  The only thing you have to watch out for is 
>> if the raw floating-point format between your two
>> machines is different.  But between x86-family machines, it's all the same.
>> -- 
>> Marcus Leech
>> Principal Investigator
>> Shirleys Bay Radio Astronomy Consortium
>> http://www.sbrac.org
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