Unwanted output signal when Linux boots up

Hello everyone,

(PicoZed SDR + breakout carrier + kernel v4.6.0)

Every time I boot up the platform, when kernel is loading and until I execute my program, some signal appears at the TX output:

Why? How to solve it? I suspect it could be the oscilloscope application auto-starting up, maybe? (PicoZed doesnt allow to connect a monitor nor I cant see any oscilloscope related process using htop), if so.. where's the script that autoexecutes it?

And also: when I want to finish my custom program with CTRL+C, I've got a handler that destroys the iio_context, iio_buffers, etc. but when they are destroyed, the radio starts transmitting some undesired signal. I solved this configuring the TX attenuation ("out_voltage0_hardwaregain") to its maximum before exiting the program, but it does not look like the right way to do it. Any suggestion?

Regards,
Leroy.

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  • 0
    •  Analog Employees 
    on Jan 2, 2017 10:18 AM

    Hi,

    The HDL reference design contains a DDS that is active by default that will generate a tone. The DDS can be enabled/disabled by writing the out_altvoltage0_1A_raw and similar attributes.

    Unfortunately the DDS is enabled by default in the driver. If you want to disable it you need to patch the driver and replace cf_axi_dds_datasel(st, -1, DATA_SEL_DDS); with cf_axi_dds_datasel(st, -1, DATA_SEL_ZERO); in the driver probe function.

    - Lars

Reply
  • 0
    •  Analog Employees 
    on Jan 2, 2017 10:18 AM

    Hi,

    The HDL reference design contains a DDS that is active by default that will generate a tone. The DDS can be enabled/disabled by writing the out_altvoltage0_1A_raw and similar attributes.

    Unfortunately the DDS is enabled by default in the driver. If you want to disable it you need to patch the driver and replace cf_axi_dds_datasel(st, -1, DATA_SEL_DDS); with cf_axi_dds_datasel(st, -1, DATA_SEL_ZERO); in the driver probe function.

    - Lars

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