GNU Radio, One Step at a Time

It is better to remain silent and be thought a fool than to open one's mouth and remove all doubt -- Abraham Lincoln · real fast

Thanks for the thoughts Sean. I hadn't thought of calling early to      give the tuner time to settle. I'll also have a look at the burst      tagger example as you suggested. I think I should be able to make a      block with only an input and put it in parallel with the other      blocks in my circuit. This should save some processing power in not      needing to copy the samples to the output. I guess what I was really      asking was whether it had to accept samples at all? As in, could a      block be made with no input or output and would its work function be      called at a set interval of time (or even at all)? Probably not a      request made often and I don't think it would take much extra      processing power to just feed it the samples. Still, I thought it      was worth looking into.

      -Dan

      On 6/29/2012 7:31 PM, Nowlan, Sean wrote:                                                You              can put a block in sequence with the samples that does two              things in the work() function:              

          1)                     copy              the input buffer to the output buffer using memcpy or              something similar since it doesn’t look like you need to              process the samples at all
          2)                     keep              track of “number of samples remaining before re-tune” in a              local variable that you set to NSAMPS_PER_TUNE, and              decrement it by noutput items as you described. If this              variable gets down to 1 (or 0?) re-set it to NSAMPS_PER_TUNE              and call the set_command_time() function to retune. You’ll              have to follow the lead of the burst tagging example to know              precisely what absolute time you need to retune, and you              also have to make sure the re-tune command gets called with              some lead-time, so I’m not quite sure how to handle this.

          This              is just a rough guess of how to do it; I’m sure there are              other nuances. With this approach you shouldn’t need to              worry about how many samples were passed to your work()              function since you always decrement your count variable by              how many you received.

          Hope              that helps!

          Sean

          From:              discuss-gnuradio-bounces+sean.nowlan=gtri.gatech.edu@gnu.org  [mailto:discuss-gnuradio-bounces+sean.nowlan=gtri.gatech.edu@gnu.org]              On Behalf Of Daniel Labarowski
              Sent: Friday, June 29, 2012 4:21 PM
              To: discuss-gnuradio@gnu.org
              Subject: [BULK] [Discuss-gnuradio] How many samples              per call to work function?
              Importance: Low

          Hello,
            I am going to be making a C++ block which will either change            the value of a variable (which would be passed to it by a            pointer) or call the tune function of a USRP sink (passed by a            pointer) after a certain number of samples have been passed to            the block. This is related to my question here.            In order to do this, I need to establish how often the            work function is called. From my past experience writing            GNURadio signal processing blocks, it looks like around 8190            samples are passed to the blocks work function each time it is            called, but this tends to vary wildly. Also, I haven't tested            whether this is dependent on data format of the input/output.            My current plan to build the block is to increment a (local,            not the on being passed) variable by noutput items each time            the work function is called. Once a certain number of samples            have been handled by the block, I will change the frequency. I            was wondering if it is even possible to construct a block with            no output or input, and if it is possible whether the work            function would ever get called and whether its noutputitems            (or ninputitems) would correspond to the number of samples            flowing through the rest of the flowgraph? If it cant be done            this way, I suppose it would be no real issue to give the            block an input so that it can count ninputitems then just not            do anything with the input items. Just trying to get a feel            for the best way to do this and to find out, in general, how            frequently the work function of the block is called and how            many samples are passed with each call? Thanks!

            -Dan

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