|
| From: | Justyn |
| Subject: | Re: [Discuss-gnuradio] WBX Dual Receiver |
| Date: | Tue, 23 Feb 2016 21:24:53 -0800 |
| User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 |
Now the issue is that with GRC, there's no way to use timed-commands directly, so you end up either coding in naked python/C++ yourself, or modifying the code generated by GRC to wrap the tuning functions in UHD timed commands.
Timed commands are the mechanism for time synchronization I was looking for, I think. I have a sample C++ application that I've written a while ago to directly interface with the UHD. Although if there's a more complete example, I would like to see that.
If I get a MIMO cable, can I avoid these timed events, and possibly use GRC? The application I'm working on serves a primary purpose, but is also meant as a learning experience for a group of students so keeping it within GRC would be ideal for future development.
-- Justyn On 02/23/2016 08:46 PM, Marcus D. Leech wrote:
On 02/23/2016 11:34 PM, Justyn wrote:Assuming that you have an external reference, and 1PPS to time-synchronize them, and you use timed-commands to properly assert the phase-resynch logic in the synthesizers, then yes, with the proviso that WBX in particular uses a 2XLO mixer, which has a 180 deg phase ambiguity--since there's no way to predict or control the start state of the flip-flop inside the mixer that's used as a phase-splitter. So they'll either be aligned, or 180deg out-of-phase.Makes sense. If I can ask a follow up here:1) If I instead use 2 USRPs connected via an external reference clock and an Ethernet switch for receiving data, will they be phase-aligned? If I understand what's going on in the context of the ref clock, I think this is a yes.If you have both USRPs in a common multi_usrp object, then their outputs will be time-aligned. The same comments above about using timed-commands for tuning, and the 180deg phase-ambiguity continue to apply here.However,2) On the TX end, if I use two USRPs connected to an Ethernet switch, and synchronized by an external clock connected to the ref clock port, is there any way I can guarantee that the first samples of each are sent out at the same "time" (I don't know what the appropriate term would be here, time, clock cycle, ref clock tick, etc)? I suspect that unless there's a mechanism that does this, this is a no.Now the issue is that with GRC, there's no way to use timed-commands directly, so you end up either coding in naked python/C++ yourself, or modifying the code generated by GRC to wrap the tuning functions in UHD timed commands.-- Justyn On 02/23/2016 08:26 PM, Marcus D. Leech wrote:On 02/23/2016 11:22 PM, Justyn wrote:There is only a single receive chain on a WBX card--there are, granted, two ANTENNA PORTS that may be selected that the receive chain attaches to, but there really is only one receive chain on a WBX card.Hello,I'm experimenting with the MIMO capabilities of the N210s with WBX daughter cards and seeing how far I can get before I need the MIMO breakout cable or GPSDO.One of the first things I'd like to see is if both receivers on the WBX daughter card can run at the same time (TX/RX and RX2).Unfortunately, if I add two USRP source blocks with the same IP to my flow graph and try it out, I get D's on the output.According to http://files.ettus.com/manual/page_general.html#general_ounotes, it seems that I'm getting "discontinuous packets" and are subsequently dropping data (which I can confirm). I assume it's because I'm receiving data packets with the same source address, and probably duplicated sequence numbers which GNU Radio thinks are discontinuous.Is there a way around this? Is this a bug? It seems if I have the bandwidth and physical hardware, I should be able to leverage those capabilities, no?This USRP and my workstation are connected through a switch, but if I add a separate identical N210 with WBX to the switch, I get both sets of data, so it's not a bandwidth issue.-- JustynThe fact that you have two distinct UHD/USRP objects trying to communicate with the same physical USRP is going to create a fair amount of confusion in the lower layers which will result in unpredictable behaviour._______________________________________________ Discuss-gnuradio mailing list address@hidden https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
| [Prev in Thread] | Current Thread | [Next in Thread] |