Re: USRP, GPIO toggling and Gnuradio

[Marcus D. Leech]

On 2021-09-10 10:18 a.m., Dobler, Anton wrote:

Dear all, 

I am currently trying to write an OOT block to switch a GPIO pin high or low depending on the input signal. So far it has worked with the configuration of the pins and I can also switch the pins according to the input signal in a relatively simple flowgraph consisting of a signal generator that produces a square wave signal. 

The block's work function looks like this:

int GPIO_IO_impl::work(int noutput_items,

            gr_vector_const_void_star &input_items,

            gr_vector_void_star &output_items)

    {        

        

        const float *in_signal = (const float *) input_items[0];

       

        for(int i=0; i < noutput_items; i++) {

           

            if(in_signal[i] >= d_threshold)

            {

                 _dev->set_gpio_attr(gpio, std::string("OUT"), "HIGH", 0xffffffff)                 

            }

            if(in_signal[i] < d_threshold)

            {

                 _dev->set_gpio_attr(gpio, std::string("OUT"), "LOW", 0xffffff);

            }

        boost::this_thread::sleep_for(boost::chrono::nanoseconds((unsigned long long)d_samp_period));

        }

        return noutput_items;

    }

The sleep function is important in that without it, regardless of the sampling rate of the square wave signal, the pin is switched with a period of 20us. If I use the sleep function, the whole thing works better, but only up to a sampling rate of about 20kHz. I have read a little bit about the function of the scheduler in GNURadio, but I did not find a solution.

Starting from the standing approach, I have tried using both Timed Commands and Boost Signals, with the result that the pins are switched completely asynchronously. Since I don't really know what to do at this point, I wanted to ask if any of you had experience with this kind of OOT block in GNURadio.

​

Best regards, 

Anton

    Could you clarify--you WANT the pins to be switched at a very high
    rate--that is you expect your input signal to be switching between
    thresholds with a period smaller than 20us?