[USRP-users] Standalone signal generator on B205mini

Ian Buckley ianb at ionconcepts.com
Fri Mar 29 02:06:39 EDT 2019


To activate TX streaming in the radio without modifying UHD you are going to have to supply some type of TX sample stream to the USRP. It can be at pretty much any rate and can be completely discarded after it’s depacketized and the corresponding ACK’s returned to the Host. The rate it’s sent by UHD to the USRP is paced entirely on how fast you accept the data into the radio…in a normal USRP the back pressure created by the interpolation logic programming from sample_rate to radio_clk, throttles the USB TX data rate via the ACK’s returning to the Host. Thus if you discard TX data at the entry to the radio very slowly (10’s-100’s KiloSample/Sec) then you will only use a very small part of the available USB bandwidth for this dummy sample stream. You will be free to generate your own TX data in custom H/W at the full radio_clk, or fraction there of. If you want to test your USB bandwidth then configure a UHD USRP Source for your application RX sample rate (preferably doing some type of representative CPU processing on the host to simulate your application load) and a UHD USRP sink driven from a constant source for the minimum possible TX sample rate …if there are no overflows/underflows then likely you have a viable approach to your design problem.

Are you wanting to generate the pulses at a fixed interval or intermittently? Even if you want to generate a very fast pulse train from your signal generator logic, you could use the TX stream as a low data rate “enable” or “trigger” stream…it would be an easy way to gain control over pulse timing etc without creating new programming registers inside the USRP that need host interaction.

> On Mar 28, 2019, at 3:07 AM, Justo Ramos, Diego <djusto at indra.es> wrote:
> 
> Hello Ian,
>  
> I want a continuous TX  of a generated signal, because I want to use the USB exclusively for RX. I don't know if I can configure by UHD this option at first time, without sending data all time and modifying the input TX data of the b205_io block with my desired signal. Is this option of configuration possible? I think that with that option I could accomplish the 3 tips that you wrote.
>  
> Thanks for your answer.
>  
> Regards,
> Diego
>  
> De: Ian Buckley <ianb at ionconcepts.com <mailto:ianb at ionconcepts.com>> 
> Enviado el: Wednesday, March 27, 2019 4:50 AM
> Para: Justo Ramos, Diego <djusto at indra.es <mailto:djusto at indra.es>>
> CC: usrp-users <usrp-users at lists.ettus.com <mailto:usrp-users at lists.ettus.com>>
> Asunto: Re: [USRP-users] Standalone signal generator on B205mini
>  
> I can’t give you a specific solution Diego because there are a lot of things here that *could* be the issue.
> However in general my tips for hacking fast custom B2xx FPGA images are:
> 1) Do it in such a way that UHD can not tell you changed the FPGA.
> i.e All register transactions should work as expected from the perspective of UHD (Understand though it doesn’t “know” if the transaction did what it expected, only that it got an acknowledgement)
> If you want to transmit then still send a sample stream to the USRP even if you discard it after it is acknowledged by the USRP (It can be a much lower sample rate than your custom logic outputs, you control radio_clk directly with master_clock_rate, sample rate controls the interpolation ratio down from radio_clk)
> 2) Use the driver functionality of UHD to control all the H/W. Really you don’t want to debug driver style code if you are in a hurry, especially the transceiver.
> 3) Don't touch the logic that interfaces immediately to the FPGA pins so as too preserve off-chip timing…a lot of work went into qualifying that.
> -Ian
>  
> On Mar 26, 2019, at 10:07 AM, Justo Ramos, Diego via USRP-users <usrp-users at lists.ettus.com <mailto:usrp-users at lists.ettus.com>> wrote:
>  
> Hello all, 
>  
> I have an B205mini board and I'm interested in modifying the internal TX block of the FPGA, to be an standalone signal generator.
>  
> I created a custom block that generates a signal, in this case a pulse generator, with the two components of 12 bits for I and Q. Then I connect these two components into  b205_io's tx_i0 y rx_i0. I use the radio_clk as clock to generate samples of the signal. 
>  
> Finally I remake the binary files of the FPGA and I reprogram the B205mini, but when I use the Spectrum Analyzer I don't have any signal  on the TX frequency.
>  
> I don't know if I have to change the clock for generation of samples or activate another signal. Could someone give me an advice to achieve custom transmission from the FPGA?
>  
> Thanks you.
>  
> Best regards,
> Diego
>  
> 
> Este correo electrónico y, en su caso, cualquier fichero anexo al mismo, contiene información de carácter confidencial exclusivamente dirigida a su destinatario o destinatarios. Si no es vd. el destinatario indicado, queda notificado que la lectura, utilización, divulgación y/o copia sin autorización está prohibida en virtud de la legislación vigente. En el caso de haber recibido este correo electrónico por error, se ruega notificar inmediatamente esta circunstancia mediante reenvío a la dirección electrónica del remitente.
> Evite imprimir este mensaje si no es estrictamente necesario.
> 
> This email and any file attached to it (when applicable) contain(s) confidential information that is exclusively addressed to its recipient(s). If you are not the indicated recipient, you are informed that reading, using, disseminating and/or copying it without authorisation is forbidden in accordance with the legislation in effect. If you have received this email by mistake, please immediately notify the sender of the situation by resending it to their email address.
> Avoid printing this message if it is not absolutely necessary.
> _______________________________________________
> USRP-users mailing list
> USRP-users at lists.ettus.com <mailto:USRP-users at lists.ettus.com>
> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com <http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com>
>  
> 
> 
> Este correo electrónico y, en su caso, cualquier fichero anexo al mismo, contiene información de carácter confidencial exclusivamente dirigida a su destinatario o destinatarios. Si no es vd. el destinatario indicado, queda notificado que la lectura, utilización, divulgación y/o copia sin autorización está prohibida en virtud de la legislación vigente. En el caso de haber recibido este correo electrónico por error, se ruega notificar inmediatamente esta circunstancia mediante reenvío a la dirección electrónica del remitente.
> Evite imprimir este mensaje si no es estrictamente necesario.
> 
> This email and any file attached to it (when applicable) contain(s) confidential information that is exclusively addressed to its recipient(s). If you are not the indicated recipient, you are informed that reading, using, disseminating and/or copying it without authorisation is forbidden in accordance with the legislation in effect. If you have received this email by mistake, please immediately notify the sender of the situation by resending it to their email address.
> Avoid printing this message if it is not absolutely necessary.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/attachments/20190328/489b08cf/attachment.html>


More information about the USRP-users mailing list