This is my first SAMA5D4 firmware that takes a reasonable sample of audio range signals.

I'm using the ADC buffer mechanism. The converter fills the buffer in the background.

I'm reading the values and log them. Later I'll use them to drive the light organ of the enchanted table.

What's Happening in the Firmware?

I'm doing exactly the same as what's documented on IioAdcDriver < Linux4SAM < TWiki.

But in C++. You can find the instructions back in the code.

For clarity, I'm using the same comments as on the AT91 pages.

Set up the channels in use

linux

echo 1 > /sys/bus/iio/devices/iio:device0/scan_elements/in_voltage0_en

c++

      ofstream osChannel("/sys/bus/iio/devices/iio:device0/scan_elements/in_voltage0_en", ios::out);
      if (osChannel.is_open()) {
        osChannel << "1";
        osChannel.close();
      } else {
        cout << "Unable to open file " << "/sys/bus/iio/devices/iio:device0/scan_elements/in_voltage0_en" << "\n";
      }

Set up the trigger we want to us

linux

echo "fc034000.adc-dev0-continuous" > /sys/bus/iio/devices/iio:device0/trigger/current_trigger

c++

      ofstream osTrigger("/sys/bus/iio/devices/iio:device0/trigger/current_trigger", ios::out);
      if (osTrigger.is_open()) {
        osTrigger << "fc034000.adc-dev0-continuous";
        osTrigger.close();
      } else {
        cout << "Unable to open file " << "/sys/bus/iio/devices/iio:device0/trigger/current_trigger" << "\n";
      }

Set up the buffer length

linux

echo 100 > /sys/bus/iio/devices/iio:device0/buffer/length

c++

      ofstream osLength("/sys/bus/iio/devices/iio:device0/buffer/length", ios::out);
      if (osLength.is_open()) {
        osLength << MUESTRAS;
        osLength.close();
      } else {
        cout << "Unable to open file " << "/sys/bus/iio/devices/iio:device0/buffer/length" << "\n";
      }

Enable the capture

linux

echo 1 > /sys/bus/iio/devices/iio:device0/buffer/enable

c++
      ofstream osEnable("/sys/bus/iio/devices/iio:device0/buffer/enable", ios::out);
      if (osEnable.is_open()) {
        osEnable << "1";
        osEnable.close();
      } else {
        cout << "Unable to open file " << "/sys/bus/iio/devices/iio:device0/buffer/enable" << "\n";
      }

After that point, the ADC starts filling the buffer - available as character device  /dev/iio:device0.

I then go on and read these 128 samples of the buffer. After that, my code will go to do the light organ work - a topic for the next post.

There's still some dodgy code in my program. My algorithm to read from that character device isn't good.

I do know how to do it properly (I have the c example code from generic_buffer.c available).

I was just hoping that I could simplify that code using a c++ character stream. I just don't seem to be able to use the stream mechanism reliable with a volatile character device yet.

I sometimes receive the two bytes that form my value in reverse order. I know that's me, because the sample code does it just fine. So there's still work to do.

  while(1) {
    ifstream myfile(fileName, ios_base::binary);
    if (myfile.is_open()) {




      for( i=0; i < MUESTRAS; i++) {




        myfile >> uSampleA;
        myfile >> uSampleB;


        /**
         * Obviously, I don't know what I'm doing here.
         * I need to study generic_buffer.c to really understand
         * how to interpret /dev/iio:device0
         * I have a 10 bits result, most likely stored in 2 bytes
         * But the way I'm reading it back seems to give a random
         * order of the high and low bytes
         *
         * I'd better start learning the way to properly read the buffer
         * but for my light organ, the errors are in the noise range
         */


        uShiftedSample = uSampleA << 8;
        uShiftedSample |= uSampleB;


        if (uShiftedSample > 1023U) {
          uShiftedSample = uSampleB << 8;
          uShiftedSample |= uSampleA;
        }


        //cout << uSampleA << " " << uSampleB << " " << uShiftedSample << "\n";


//        data[i] = uShiftedSample/4-128; //Convertimos de 0..1024 a -128..127
        data[i] = uShiftedSample; //Convertimos de 0..1024 a -128..127
        im[i] = 0;                    // parte imaginaria = 0


      }


      cout << "\nsamples :\n";
      for( i=0; i < MUESTRAS; i++) {
        cout << (int)data[i] << ",";
      }
      cout << "\n";




    } else {
      cout << "Unable to open file " << fileName << "\n";
    }


    // taken out of sample loop
    myfile.close();
  }

For my light organ however, this sample quality will do.

In the next installment I'll transpose the samples to the -128..127 range.

Then to go through the FFT library, and I'll chop them up in bass, middle and treble...