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From: | Tom Hendrick |
Subject: | [Discuss-gnuradio] USRP Streaming Latency |
Date: | Mon, 28 Mar 2011 12:09:51 -0700 (PDT) |
Hi all, I'm having some issues with the USRP and some latency in the output signal. I am using a C++ program which modulates a signal and writes to a file continuously. When I use a normal file, the C++ program output looks perfect. When I use a script made in GRC to read the C++ output file, the USRP generated signal also looks perfect with an oscilloscope. Now to get the process real-time, when I use mkfifo to tie the C++ and GRC script together, I notice a problem. The C++ program constructs a packet and then flushes and repeats continously. I'm sure this is less than the 64KB buffer size with FIFOs. The GRC script reads from that file and I see the signal output showing the modulated blocks, but I notice it is not continuous and there seems to be 1-2 seconds of zero signal, every 5 seconds or so. I also see uU from the GRC script output about every 5 or so seconds. Does anyone have any idea if this is a FIFO problem, or is it a USRP/GRC issue? I am using a Duo core SU7300 laptop so I would think it should run OK real-time unless the C++ and GRC script demand much more processing power when used at the same time. Does anyone know any tricks I can try? Thanks, Tom |
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