[USRP-users] Standalone signal generator on B205mini

Ian Buckley ianb at ionconcepts.com
Tue Mar 26 23:50:01 EDT 2019

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.

> On Mar 26, 2019, at 10:07 AM, Justo Ramos, Diego via USRP-users <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
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