On Sun, Mar 8, 2020 at 2:15 PM Marek Dopiera <[email protected]> wrote:
> On 08/03/2020 00:49, Brian Padalino wrote: > > On Sat, Mar 7, 2020 at 6:02 PM Marek Dopiera via USRP-users > > <[email protected] <mailto:[email protected]>> wrote: > > I had to do this recently with an X310 application. Originally I tried > > timed bursts where I would give the full burst to UHD and hope it would > > get things sent since the burst was supplied all at once. This was not > > my experience and exposed some bugs which may still be outstanding. > > > > My next approach was to simply have a writer thread which would check a > > transmit buffer/FIFO and, if there was nothing to transmit, would stuff > > a minimal amount of zeros into the data stream. This call to send() of > > the zero stuffed data would fill up the buffers downstream on the device > > until the backpressure from the device naturally limited the > > transmission. This approach worked very well for my application. It > > kept the minimal buffering with almost no overhead and I knew the > > latency through the system was basically the amount of time to consume > > the buffer. > > Hi Brian, > thank you for your response. > > I'm doing pretty much what you described - a FIFO with separate threads, > and pushing to tx_stream::send until it blocks. In my case I'm actually > sending data, not zeros, though. > > I do not have control over how much data gets into the buffers before > tx_streamer::send() starts blocking, though - I'm guessing I can go > lower than that, but for that to work I need to know when the data is > actually sent. > The amount of buffering (software) should be controllable via arguments to UHD, and the amount of buffering in the hardware should be fixed based on which product you're using. Just for clarity, the reason for sending zeros is to maintain and keep a stream with no underflows as well as keep the buffering pipeline full since getting UHD to try to be responsive to sending bursts at a high sample rate without underflows didn't work well for me. What type of response time are you looking for when it comes to sending data versus nothing? Brian
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