I'm not really sure about whether you can get a work function to be called at a set interval. One thing comes to mind though. I suppose you could make this block into a data sink that's in parallel with your actual data flow. Then you can just use the size of each incoming buffer when work() is called to determine when you need to retune. Just ignore the actual incoming data itself.
However, this may not work because the USRP sink/source block is the actual object that provides access to the set_command and set_command_time methods. Now that I think of it, you may have to edit the USRP source/sink block to directly schedule retuning in the work() function using an algorithm like the one I mentioned earlier, or else enhance it to act on incoming "tune" tags in a similar way to how burst commands are done, and then tag samples in an upstream block with the "tune" tag. Does that make sense? Sean From: discuss-gnuradio-bounces+sean.nowlan=gtri.gatech....@gnu.org [mailto:discuss-gnuradio-bounces+sean.nowlan=gtri.gatech....@gnu.org] On Behalf Of Daniel Labarowski Sent: Saturday, June 30, 2012 11:21 PM To: discuss-gnuradio@gnu.org Subject: Re: [Discuss-gnuradio] How many samples per call to work function? 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....@gnu.org<mailto:discuss-gnuradio-bounces+sean.nowlan=gtri.gatech....@gnu.org> [mailto:discuss-gnuradio-bounces+sean.nowlan=gtri.gatech....@gnu.org] On Behalf Of Daniel Labarowski Sent: Friday, June 29, 2012 4:21 PM To: discuss-gnuradio@gnu.org<mailto: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. <http://old.nabble.com/Tunning-USRP-From-Seperate-C%2B%2B-Block--td33970855.html#a33970855> 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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