I've been working on getting the usrp working with a USB full speed interface connected to an OMAP starter kit (OSK) board from TI. I'm not using GNU Radio, but the OSSIE open source SCA. The OSK only has a USB 11 controller that sends 64 byte packets, not the 512 byte packets sent by USB2.0 high speed interfaces.
The code I have uses the usrp-0.12 package to communicate with the USRP. This email is mainly of interest to people interested in low level USRP interfacing and the FPGA to FX2 interface. I have a waveform that generates random BPSK that works fine on a PC with is USB high speed interface. The output is raised cosine pulse shaped and I monitor it on a Tektronix signal analyzer. When I run the waveform on a PC with a USB2.0 hidg speed interface I see a good eye diagram. When I compile the code for the OSK, I see two symbols transmitted, then dead air. Two symbols is 64 bytes (2 symbols x 8 sample/symbol x 4 bytes/sample), then there are 512 - 64 bytes of no signal. It feels like the 64 byte packets are read into a buffer of 512 bytes, where all the un-written bytes are zeros. It feels like somewhere in the USB chain, I send the 64 byte packet, then something reads the 64 bytes and zero pads the packet to 512 bytes. I suspect the FPGA tries to read 512 bytes from the FX2 chip, but that is only because this is the area of the code I least understand :) I see that some people on this list (beyond Matt and Eric) are interested in the signal flow from the PC to the ADC/DAC's so I'm hoping someone has some suggestions. Philip _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
