Re: [Discuss-gnuradio] how to manage time!

[Mostafa Alizadeh]

Hi Marcus, 

I actually want to implement a transmitter. So in this transmitter different data streams come from different sources with different rates (or sample rates). Then all of these streams gather together in a block, may I call it "Collector" then it sends the gathered data stream to the USRP sink. The Collector block should gather the data stream in some specific manner to put the streams in a particular frame!

The only thing I don't know here is how could I generate these different-rate data?

At the receiver we don't have any problem like this one, I think, because we can set the sample rate for USRP then after detection of the data streams in the frame we actually could find the transmitted-dirfferent-rate streams with different rate. :)

Any idea please? 

best, 

On Fri, May 9, 2014 at 12:23 AM, Marcus Müller <address@hidden> wrote:

hi Mostafa,

a fixed item rate just happens coincidentally when using actual hardware. In digital signal processing you really usually don't care, as long as latency constraints are met. typically, you can't even do that at all, because GNU Radio blocks tend to process samples en block.

maybe tell us a little bit why you want to have a physical item rate, things would clear up a bit:-)

greetings,
Marcus

On May 8, 2014 9:37:32 PM CEST, Mostafa Alizadeh <address@hidden> wrote:

Hi Marcus, 

I did know about the Throttle block and which doesn't do anything with data just control its passing. My question is how to generate a bit stream(I say bit and we could simply call it item), say random, with specific sample rate just as audio source do! I had a glimpse at the source code of portaudio_source.cc in gnuradio files but I didn't find out it easy to understand. :( 

any idea? 

best, 

 

On Thu, May 8, 2014 at 10:03 PM, Marcus Müller <address@hidden> wrote:

Hi Mostafa,

I'm not really sure I understand your question:
there is different "times" in DSP:
1. the times relative to the "information theoretical world", which
increases with 1/f_sample per sample
2. the time relative to the computing machine, which just runs along
while the computer is busy computing

Throttle is *explicitely* just a throttle block. For a *purely
simulating* flowgraph, you can use it to *limit CPU usage*. it has no
other purpose. It is a very very rough mapping of the first time to the
second one. It really has no data effect. I emphasisize this, because
that mistake is made so often: it does not change the samples at all. it
just limits the speed they are processed with.

I think your question is "I want to have a sample stream that contains
1000 bits of information for each second worth of samples". So you have
to calculate how many samples you have per bit at your specified
sampling rate and use that.

Since you write "I saw the trottle block but I don't know what it does",
I think you can learn interesting things by working through the
Tutorials on
http://gnuradio.org/redmine/projects/gnuradio/wiki/Tutorials from top to
bottom. This will clear up a lot of things!

Greetings,
Marcus

On 08.05.2014 19:24, Mostafa Alizadeh wrote:
> Hello everybody,
> I want to have a block of, for example, bit generator, which generates 1000
> bps. How could I manage the time in a thread (or equivalently in a block)??

> *Or saying in general, how could I manage timing for passing data between
> blocks!?*

>
> I saw the "Throttle" block of gnuradio in c++ but I didn't how it works!!
>
> best,
>
>
>

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> Discuss-gnuradio mailing list
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