# How to manage time! **URL:** \ **Category:** GNU Radio\ **Created:** [May 8, 2014, 7:25pm UTC](https://www.ruby-forum.com/t/how-to-manage-time/240998 "2014-05-08T19:25:13Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\ **Post date:** [May 8, 2014, 7:25pm UTC](https://www.ruby-forum.com/t/how-to-manage-time/240998/1 "2014-05-08T19:25:13Z")
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, ---
**Author:** ![mostafa\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/5e9695/32.png) [@mostafa\_a](https://www.ruby-forum.com/u/mostafa_a)\ **Post date:** [May 8, 2014, 7:35pm UTC](https://www.ruby-forum.com/t/how-to-manage-time/240998/2 "2014-05-08T19:35:03Z")
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](http://gnuradio.org/redmine/projects/gnuradio/wiki/Tutorials) from top to bottom. This will clear up a lot of things! Greetings, Marcus ---
**Author:** ![mostafa\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/5e9695/32.png) [@mostafa\_a](https://www.ruby-forum.com/u/mostafa_a)\ **Post date:** [May 9, 2014, 4:06am UTC](https://www.ruby-forum.com/t/how-to-manage-time/240998/3 "2014-05-09T04:06:35Z")
On Fri, May 9, 2014 at 1:24 AM, Mostafa A. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)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!! Let me put the answer into layman’s terms. 1). If there is any USRP (or audio block) in the flowgraph, then you just need to calculate a sampling rate (samp\_rate) value and configure this to your bit-generator block. If this samp\_rate value is correct, your bit-gnerator block will automatically generates output at 1000 bps. To calculate this samp\_rate, you need to look at the flow graph, how the blocks are interconnected. 2). If there is no USRP (nor audio block) in the flowgraph, it is not so critical whether your bit-generator block actually generates output at 1000 bps or 10,000 bps or 100,000 bps. This is because software simulation can be a fast-forward version of the actual speed. 3). Throttle block is needed only when there is no USRP (nor audio block) in your flow graph, to increase user experience. The settings of the throttle block has no effect on your simulation result. ---
**Author:** ![mostafa\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/5e9695/32.png) [@mostafa\_a](https://www.ruby-forum.com/u/mostafa_a)\ **Post date:** [May 10, 2014, 1:19am UTC](https://www.ruby-forum.com/t/how-to-manage-time/240998/4 "2014-05-10T01:19:08Z")
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, ---
**Author:** ![mostafa\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/5e9695/32.png) [@mostafa\_a](https://www.ruby-forum.com/u/mostafa_a)\ **Post date:** [May 10, 2014, 2:21am UTC](https://www.ruby-forum.com/t/how-to-manage-time/240998/5 "2014-05-10T02:21:32Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi Mostafa, you will have to have all your sample streams at the same nominal sampling rate (which again has nothing to do with the item rate you described). You do that by resampling. How you combine these streams is obviously totally part of what your application has to define. Greetings, Marcus On 09.05.2014 08:14, Mostafa A. wrote: > The only thing I don’t know here is how could I generate these > > > process samples en block. > > > > > Hi Marcus, I did know about the Throttle block and which > > > > > > > 1/f\_sample per sample 2. the time relative to the computing > > > > > > > > > passing data > > > > – Sent from my Android device with K-9 Mail. Please excuse my > > brevity. > > \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Discuss-gnuradio > mailing list [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 Comment: Using GnuPG with Thunderbird - [http://www.enigmail.net/](http://www.enigmail.net/) iQEcBAEBAgAGBQJTbICZAAoJEBQ6EdjyzlHty44IAIPwu9yqultka/oTr5zQq/IY BlI+b9EE7KXUaxzsjLst1puw0ckiQ5RoDY/fXr9eA+DV9HBGgCFtwCobkn4MTLm0 aKU7DEpJfVpGDhFSmTA9Q/7EJupprccvK9AR4MC8zKx/WyS8avQk+9kJaeeDw7CZ R94CH/whUDrfyeLLMyzc2cXQMEdHEBj5dqfi9ybNw2EgtsxXM/urBBgK/hTbucvA sWFcJTD3h3aOKold/Kjn8ksGDmjrfIs5Ym/We62h+sUS+DKDHX3/AnEHA2p7pFGc 9CgxPfTUs6LYKYxogzyoQnx1DtaNVrDq6gI//YceT8WLV4ADTY4xK5U+B8ABjpo= =2SWS -----END PGP SIGNATURE----- ---
**Author:** ![mostafa\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/5e9695/32.png) [@mostafa\_a](https://www.ruby-forum.com/u/mostafa_a)\ **Post date:** [May 10, 2014, 2:37am UTC](https://www.ruby-forum.com/t/how-to-manage-time/240998/6 "2014-05-10T02:37:09Z")
On Fri, May 9, 2014 at 2:14 PM, Mostafa A. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)wrote: > 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). I feel this was actually the same problem, at [http://gnuradio.4.n7.nabble.com/set-relative-rate-td46167.html](http://gnuradio.4.n7.nabble.com/set-relative-rate-td46167.html) In this thread Tom’s solution was to set the IO signature as: gr::io\_signature::make2(2, 2, 1000_sizeof(type0), 1_sizeof(type1)) Whereas Marcus suggests to use resampler block, I agree this approach is simpler and less confusing especially to new comers like Mostafa. ---
**Author:** ![mostafa\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/5e9695/32.png) [@mostafa\_a](https://www.ruby-forum.com/u/mostafa_a)\ **Post date:** [May 10, 2014, 7:13am UTC](https://www.ruby-forum.com/t/how-to-manage-time/240998/7 "2014-05-10T07:13:53Z")
Pls stay on the list. ---
**Author:** ![mostafa\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/5e9695/32.png) [@mostafa\_a](https://www.ruby-forum.com/u/mostafa_a)\ **Post date:** [May 10, 2014, 7:28am UTC](https://www.ruby-forum.com/t/how-to-manage-time/240998/8 "2014-05-10T07:28:37Z")
Hi Marcus and Activecat, Thank to you Activecat for your proposed solution to the question. The method is very interesting to me to use _forecast_ and _consume_ or setting right values in the io\_signature. As Marcus said it’s better to use _interpolator_ or _decimators_ to change the rates and I know it’s the best. Marcus I know what you said about sampling theory. But you must notice that the higher the sampling rate, the greater the number of samples you get in a particular period of time (real world time). In your example the sine has a frequency of 1000 ( in real time) but the number of samples of that sine function, could be determined with your sampling rate. Best, ---
**Author:** ![mostafa\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/5e9695/32.png) [@mostafa\_a](https://www.ruby-forum.com/u/mostafa_a)\ **Post date:** [May 10, 2014, 8:02am UTC](https://www.ruby-forum.com/t/how-to-manage-time/240998/9 "2014-05-10T08:02:59Z")
On Fri, May 9, 2014 at 2:14 PM, Mostafa A. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)wrote: > To accomplish this, you need to forecast() and consume() different rates at different ports. Let me give you a sample code similar to your “Collector” block. Say both block A and block B are directly connected to your Collector block. Block A output rate = rate1 = 200ksps Block B output rate = rate2 = 10kbps Collector block output rate = 200kbps Below is the collector\_impl.cc: ``` namespace gr { namespace activecat { // make quad_up2::sptr quad_up2::make( float rate1, float rate2 ) { return gnuradio::get_initial_sptr (new quad_up2_impl(rate1, rate2)); } // constructor quad_up2_impl::quad_up2_impl( float rate1, float rate2 ) : gr::block( "quad_up2", gr::io_signature::make( 2, 2, sizeof(gr_complex) ), gr::io_signature::make( 1, 1, sizeof(float) ) ), d_rate1( rate1 ), d_rate2( rate2 ) { if ( (int)rate1 % (int)rate2 ) throw std::runtime_error( "quad_up1: rate1 must be exact ``` multiple of rate2" ); ``` d_ratio12 = int( rate1 / rate2 ); // equals to 20 in ``` this example ``` set_output_multiple( d_ratio12 ); } // destructor quad_up2_impl::~quad_up2_impl() { } // forecast void quad_up2_impl::forecast (int noutput_items, gr_vector_int ``` &ninput\_items\_required) { ninput\_items\_required[0] = noutput\_items / d\_ratio12; // connected to Block B ninput\_items\_required[1] = noutput\_items; // connected to Block A } ``` // general_work int quad_up2_impl::general_work ( int noutput_items, gr_vector_int &ninput_items, gr_vector_const_void_star &input_items, gr_vector_void_star &output_items) { const gr_complex *data = (const gr_complex *) ``` input\_items[0]; // connected to Block B const gr\_complex \*clk = (const gr\_complex \*) input\_items[1]; // connected to Block A float \*out = (float \*) output\_items[0]; ``` if ( noutput_items % d_ratio12 ) { std::cout << "noutput_items = " << noutput_items << ", ``` d\_ratio12 = " \<\< d\_ratio12 \<\< std::endl; throw std::runtime\_error(“quad\_up2: noutput\_items is not exact multiple of d\_ratio12”); } ``` for( int i=0; i < noutput_items; i++) out[i] = clk[i].real() * data[i/d_ratio12].real() - ``` clk[i].imag() \* data[i/d\_ratio12].imag(); ``` consume(0, noutput_items / d_ratio12); // consumes ``` data from Block B consume(1, noutput\_items ); // consumes data from Block A ``` return noutput_items; } } /* namespace activecat */ } /* namespace gr */ ``` ---
**Author:** ![mostafa\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/5e9695/32.png) [@mostafa\_a](https://www.ruby-forum.com/u/mostafa_a)\ **Post date:** [May 11, 2014, 2:44am UTC](https://www.ruby-forum.com/t/how-to-manage-time/240998/10 "2014-05-11T02:44:01Z")
Dear Activecat, To be honest, I’m still confused!! 🙂 I want to have a source which generates a stream in a specific sample rate (or approximately, in average). Take a look at Audio source block, or some other source blocks, if there any, which takes sample rate as an input. (for instance USRP source also has this kind of input) You will see options for sampling frequency in \*audio source block \*by that rate outputs samples of type float. This block that I don’t know how works, it’s somehow what I want as a source to run my signal processing chain. If I could be enable to have such source block, I have nothing else to be worry! Thanks, ---
**Author:** ![mostafa\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/5e9695/32.png) [@mostafa\_a](https://www.ruby-forum.com/u/mostafa_a)\ **Post date:** [May 10, 2014, 8:39am UTC](https://www.ruby-forum.com/t/how-to-manage-time/240998/11 "2014-05-10T08:39:49Z")
Hi Activecat, hi Mostafa, > > The only thing I don’t know here is how could I generate these > > different-rate data? > > The rate of data is really just a property of the values of the samples. > > For example, a sine with a frequency of 1000 will have a period of 32 > > samples for a sample rate of 32000, if you have the same sine at a > > sample rate of 64000, its period will be 64 samples… note that > > frequency and sample rate are all nothing but relative numbers. If you have two things in your flow graph that produce signals related to a different sampling rate (again, there is no awareness of any sampling rate at all in GNU Radio, it’s just that frequencies you specify relate to a sample rate that you or your device specify themselves), you will have to match one sample rate to the other. That means resampling. To explain using aforementioned example: if you want to make sense while adding up the two sines, you would resample the 32k sampling rate to 64k, and then add the two sample streams. This is the very basic idea of digital signal processing: you don’t really care about the rates at which signals occur - you just math them hard enough until they match your model. > > > > To accomplish this, you need to forecast() and consume() different rates at > different ports. > Not really. Usually, you use one of the existing resampler blocks. Then > you just use whatever block type with the then equally-sampled streams. There is _very_ rarely the need for implementing your own forecast with these kind of streams. For fixed ratio integral resamplers, just use the decimator or interpolator block types. I hope to conclude this thread with this. The information-theory sampling rate vs. processing item rate vs. real time problem is a tough one to get one’s head around; however, I think trying, playing around and reading up on things is the right way to go from here for you, Mostafa; it’s not very useful to discuss this on a mailing list like this, I’m afraid. Greetings, Marcus ---
**Author:** ![mostafa\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/5e9695/32.png) [@mostafa\_a](https://www.ruby-forum.com/u/mostafa_a)\ **Post date:** [May 11, 2014, 3:15am UTC](https://www.ruby-forum.com/t/how-to-manage-time/240998/12 "2014-05-11T03:15:20Z")
Hi Mostafa, again: Start trying things out! The Audio source is a hardware bound source, where theoretically sampling rate and sample production rate match. That’s only the case for hardware sources/sinks, and GNU Radio has no chance nor will to enforce that, because it is software running on a general purpose computer. Your sample stream is totally agnostic of time. And there’s absolutely no way to change that in a properly controlled manner. So stop worrying, start trying, and let’s move away from this strange thread 🙂 Greetings, Marcus ---
**Author:** ![mostafa\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/5e9695/32.png) [@mostafa\_a](https://www.ruby-forum.com/u/mostafa_a)\ **Post date:** [May 11, 2014, 3:33am UTC](https://www.ruby-forum.com/t/how-to-manage-time/240998/13 "2014-05-11T03:33:11Z")
On Sat, May 10, 2014 at 3:38 PM, Mostafa A. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)wrote: > Dear Activecat, > To be honest, I’m still confused!! 🙂 Mostafa, Marcus and I have done our best to help you. All the best.