Thank you very much for your help Josh! I'll let you know if we end up going this way in our design.
On Sun, Sep 30, 2012 at 7:01 PM, Josh Blum <j...@ettus.com> wrote: > > > On 09/29/2012 09:45 AM, Anisha Gorur wrote: > > Thanks Josh, > > What I am looking for on the TX side of things is basically the same > thing > > I have on the RX side. If I set the subdev spec on the basic RX to "A:A > > A:B" and then use usrp->set_rx_freq(uhd::tune_request_t(freq)) for each > > channel, I get two separate rx channels, both with their own IQ pairs. On > > the TX side I only manage to have one IQ pair, as in I through TX_A and Q > > through TX_B. We were trying for a 4 channel transmit on 2 USRPs, so that > > they could all be connected by s MIMO cable. One more question, when you > > say "too complicated to be worth it", generally, what kind of > modification > > would be necessary? > > The reason for the complication is there is this whole flow control > implementation for the TX. Here is my suggestion: > > On the host, interleave your MIMO channels. So send 1 TX channel where > the samples are ch0IQ0, ch1IQ0, ch0IQ1.... > > In the FPGA, a good way is to modify the top level to have two DUC > chains. See right here: > > http://code.ettus.com/redmine/ettus/projects/uhd/repository/revisions/master/entry/fpga/usrp2/top/N2x0/u2plus_core.v#L716 > > Instantiate two DUC chains. Most of the wires can stay the same. Since > this is MIMO, you want both DUC chains to have the same settings > anyways. What you want to do here is to play with the strobe_tx signal > such that every even strobe is off for DUC0 and every off strobe is off > for DUC1... thats effectively the deinterleave. Also notice how the > tx_fe outputs are connected. > > reg even; > always @(posedge dsp_clk) > if (~run_tx) even <= 0; > else if (strobe_tx) even <= ~even; > > duc_chain #(.BASE(SR_TX_DSP), .DSPNO(0)) duc_chain0 > (.clk(dsp_clk),.rst(dsp_rst), .clr(clear_tx), > > .set_stb(set_stb_dsp),.set_addr(set_addr_dsp),.set_data(set_data_dsp), > .set_stb_user(set_stb_user), .set_addr_user(set_addr_user), > .set_data_user(set_data_user), > .tx_fe_i(tx_fe_i),.tx_fe_q(), > .sample(sample_tx), .run(run_tx), .strobe(strobe_tx & even), > .debug() ); > > duc_chain #(.BASE(SR_TX_DSP), .DSPNO(0)) duc_chain1 > (.clk(dsp_clk),.rst(dsp_rst), .clr(clear_tx), > > .set_stb(set_stb_dsp),.set_addr(set_addr_dsp),.set_data(set_data_dsp), > .set_stb_user(set_stb_user), .set_addr_user(set_addr_user), > .set_data_user(set_data_user), > .tx_fe_i(tx_fe_q),.tx_fe_q(), > .sample(sample_tx), .run(run_tx), .strobe(strobe_tx & ~even), > .debug() ); > > > -Josh > > > Thanks for your time! > > -Anisha > > > > On Fri, Sep 28, 2012 at 6:36 PM, Josh Blum <j...@ettus.com> wrote: > > > >> > >> > >> On 09/28/2012 08:49 AM, Anisha Gorur wrote: > >>> Hello All, > >>> > >>> I am using a USRP N210. When i set the subdev spec for my basic RX > >>> daughterboard as "A:A A:B" I can receive two channels. However, if I > try > >> to > >>> do something similar for the basic TX I get an error like "The user > >>> specified 2 channels, but there are only 1 tx dsps on mboard 0." I > assume > >>> this is because there is only one DUC chain in the N210. Is there a way > >> to > >>> modify this so that I can have two DUC chains in the same way that I > have > >>> two DDC chains? > >>> Thanks, > >>> Anisha > >> > >> I think adding two complete DUC chains into N210 would be too > >> complicated to be worth it. > >> > >> Is there something specific that you cant do with the single DUC chain? > >> As long as the cordic is set to zero, I and Q will remain completely > >> separate from host samples, all the way to the SMA connectors A and B. > >> > >> Otherwise, perhaps you need a different rotation for I vs Q? I think > >> that would be better accomplished by two different cordics. Then perhaps > >> a custom DSP in the FPGA is for you: > >> > >> > http://code.ettus.com/redmine/ettus/projects/uhd/repository/revisions/master/entry/fpga/README.txt#L29 > >> > >> I hope that helps. > >> > >> -josh > >> > >>> > >>> > >>> > >>> _______________________________________________ > >>> Discuss-gnuradio mailing list > >>> Discuss-gnuradio@gnu.org > >>> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >>> > >> > >> _______________________________________________ > >> Discuss-gnuradio mailing list > >> Discuss-gnuradio@gnu.org > >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >> > > > > > > > -- Anisha Gorur Class of 2012 Electrical Engineering
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