Hello all,
I have been trying to understand the mechanics of stream tags and USRP. To this end, I am reading through the tags_demo.cc example found in gr-uhd/examples/c++.
The example provides two options for burst control: using SOB/EOB tags, and using tagged stream blocks. For clarity, let us assume that we choose to use SOB/EOB tags, that is, we pass an empty tsb_tag_name. This choice does not affect my question that follows later.
>From the code it looks like the flowgraph does not stay idle at any point. It takes a bunch of samples, and stamps the SOB tag along with a time tag on the first sample. The flowgraph keeps running till the burst is on. Once the number of samples in a burst are exhausted, it stamps an EOB tag. At this point, it immediately starts a new burst with an SOB tag, but with a delayed time tag to accommodate for the idle period. In contrast, the USRP transmission must stay off during the idle period.
In this flowgraph the sample rate is clearly controlled by the USRP sink hardware. If the flowgraph produces samples at this rate and does not stay idle, then will it not eventually overwhelm the USRP sink? Assuming default values of sample rate (1e6) and burst and idle time (0.1 and 0.05, respectively), the flowgraph would produce 50,000 samples in each idle period. These samples will keep on accumulating endlessly.
I believe I am missing something here, because this example has been clearly reported to work just fine. Any comments?
Thanks,
Lakshay.