Thanks Michael, So, do all "timed" commands sent to the command queue need to be in strictly ascending order (in time)? In other words, will a disordered queue always produce a Late error or does it depend on how much disordered?
Are there any other "timed" commands to worry about besides the following? - commands sent in between set_command_time() and clear_command_time() - rx and tx streaming commands that include a time_spec Rob On Tue, Oct 10, 2017 at 4:11 PM, Michael West <michael.w...@ettus.com> wrote: > Hi Rob, > > Yes, that would be a problem. There is a single command queue for both TX > and RX commands to the radio, so something has to collate the T/R switching > commands with the RX streaming command so none of the commands arrive late. > > Regards, > Michael > > On Thu, Oct 5, 2017 at 7:48 AM, Rob Kossler via USRP-users < > usrp-users@lists.ettus.com> wrote: > >> Hi Marcus, >> Still working on the same issue (sporadically). I was able to get my >> transmit pulse behaving reasonably well (using continuous Tx streaming and >> manually controlling the T/R switch using timed commands). However, I ran >> into a problem when I tried to simultaneously stream Rx data. The RX >> streaming reports a single Late command followed by numerous Timeouts. >> >> Since I am able to >> A) run my application in TX-only mode (with separate threads for transmit >> streamer and T/R switching), and >> B) to run in TX/RX mode without T/R switching >> >> I am wondering what is the source of my problem when I try to run in >> TX/RX mode with T/R switching. I am wondering if the problem could be >> related to ordering of timed commands. I have made sure that the T/R >> switching commands are sent in time-ascending order, but I have no >> synchronization between these commands and my Rx streaming command (which >> includes a time spec in the meta data). So, it is possible that my >> application is sending a tone of T/R switching commands (filling up the >> timed command FIFO) prior to sending the Rx streaming command. Would this >> be a problem? >> >> Rob >> >> >> On Tue, Sep 26, 2017 at 9:09 PM, Rob Kossler <rkoss...@nd.edu> wrote: >> >>> Hi Marcus, >>> Thanks for your response. I've been away for several days and finally >>> had the opportunity to revisit this today. >>> >>> I modified my code to manually control the TxEnable pin using timed >>> commands in order to pulse a continuously streaming TX waveform (100 >>> MS/s). This worked until I reached a limit on PRF at around 20 kHz (50 us >>> PRI). When I tried to go faster (e.g., 20 us PRI), the pulse train went a >>> bit crazy - likely from the commands arriving late. I'm guessing that >>> there is some limit to how fast I can send these GPIO commands while at the >>> same time streaming at 100 MS/s. The bad news is that this was with one >>> channel. So, I expect that when I implement with 2 TX simultaneously >>> (e.g., beamforming), I will need to send twice the number of GPIO commands >>> and thus my min PRI will jump to about 100 us (but I haven't tried this >>> yet). By the way, this was implemented with 3.9.LTS and a single 10Gbe >>> link. >>> >>> The other thing I noticed was that the RF pulse width was about 300 ns >>> shorter than expected for the specified switching times. The switch data >>> sheet indicates on/off switch times on the order of 45ns. Thus, enabling >>> and disabling of the switch could account for 90 ns, but this is still much >>> less than the observed shortfall. Not sure what the cause is. >>> >>> In the end, this may be good enough for my application. Still, I may >>> try some things in the FPGA. >>> >>> Rob >>> >>> >>> >>> On Mon, Sep 18, 2017 at 5:54 PM, Marcus Müller via USRP-users < >>> usrp-users@lists.ettus.com> wrote: >>> >>>> Hey Rob, >>>> >>>> so, it's probably the good ol' radar bandwidth conundrum: For good >>>> range resolution, you'd typically want high TX and RX bandwidth, but at >>>> least on TX, it feels kinda bad to stream a full 200MS/s to the USRP, just >>>> to be able to turn a sine wave on and off again within a few nanoseconds. >>>> And to confirm your suspicion: Yes, if you use a lower rate than that, the >>>> X310 will interpolate to the 200MS/s MCR, and that happens with a low-pass >>>> filter (to get rid of spectral aliasing in the general use case), and that >>>> "washes out" your pulses. So, meh. >>>> >>>> As long as you're not sending constantly, but more in terms of single >>>> pulses or short pulse packets, sending the signal at a full 200 MS/s might >>>> be the right thing to do – the USRP would buffer the sample packets until >>>> the TX timestamp "happens", and there's no unnecessarily high CPU load. >>>> >>>> You could also replace the DUC with a simple "repeat" NoC block. Or >>>> with an upsampler without an anti-imaging filter (ie. a zero-padder), for >>>> that manner. Or, upsample, but use the desired pulse shape as filter. >>>> >>>> 1) well, close reflections are usually very strong with radar. If >>>> you're using an external amplifier, that might be a problem. >>>> 2) There's a the auto-TX/RX switching functionality that you can use to >>>> switch when you start/stop streamers. Also, yes, antenna switches are just >>>> "normal" GPIO, so you can basically look into the daughterboard driver to >>>> see which GPIO gets toggled when you change the antenna, and do the same in >>>> your application. >>>> >>>> Hope that helps, >>>> >>>> best regards, >>>> >>>> Marcus >>>> >>>> On 09/18/2017 01:55 PM, Rob Kossler via USRP-users wrote: >>>> >>>> Hi, >>>> I am interested in implementing a pulsed CW radar using a single >>>> channel (X310/UBX) via the TX/RX antenna port. >>>> >>>> My initial implementation works, but not that well. In this >>>> implementation, I continuously stream the receiver with antenna set to >>>> TX/RX and I simultaneously send timed transmit bursts for each pulse. The >>>> USRP automatically switches the T/R switch to transmit during the transmit >>>> bursts and then back to receive when the transmit burst completes. The >>>> switch time seems good enough for my application. However, the transmit >>>> pulse doesn't look as expected at the beginning - likely due to start up >>>> filtering in the DUC. >>>> >>>> I am considering a different implementation such that transmit and >>>> receive both run continuously and I just manually "hot-switch" the T/R >>>> switch between transmit and receive using timed commands. I have 2 >>>> questions: >>>> 1) is there a problem with this approach (e.g., possibility of damaging >>>> the device)? >>>> 2) how do I manually control the T/R switch? (I am expecting I need to >>>> use the GPIO registers, but I can't find the relevant info in the manual). >>>> >>>> Rob >>>> >>>> >>>> _______________________________________________ >>>> USRP-users mailing >>>> listUSRP-users@lists.ettus.comhttp://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >>>> >>>> >>>> >>>> _______________________________________________ >>>> USRP-users mailing list >>>> USRP-users@lists.ettus.com >>>> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >>>> >>>> >>> >> >> _______________________________________________ >> USRP-users mailing list >> USRP-users@lists.ettus.com >> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> >> >
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