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  • Author Author: Jan Cumps
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Review 7: Atmel SMART SAMA5D4 Xplained Ultra - C++ ADC Example on Linux

Jan Cumps

I'm making steady progress on this drizzly day.

I have my first C++ linux program running that samples the an ADC pin on the SAMA4D4 Xplained Ultra Board.

 

In the mid 90's, I was a C++ software developer. Around that same time, the standard template library (STL) came into fashion.

It's great to use it once again.

 

image

 

Getting the ADC values

 

Once again, this is inspired by 's work on this board, SAMA5D4 Xplained Ultra - Tips and Tricks #2 - Using the built in IO and external devices.

I'm using a very similar setup as Peter, but instead of using the Linux command line to read the sample results, I've written a C++ program.

But we're both triggering a sample and reading results by accessing /sys/bus/iio/devices/iio:device0/in_voltage0_raw.

 

The schematic is very simple: a potentiometer with both ends connected to ground and 3.3V of the Xplained board. The wiper goes to A1.

To make things funny, A1 is analog port 0 in the linux mapping. (I don't know yet what A0 is, but it has a digital signal on it when I sample it with my scope.)

 

The program is cross-compiled using the GNU toolchain on a windows machine, loaded to the linux root user's home folder, and executed.

It shows a sample result in the terminal window every second.

I haven't used any of the Atmel libraries. All is done via standard file access.

 

#include <iostream>
#include <fstream>

using namespace std;

const char fileName[] = "/sys/bus/iio/devices/iio:device0/in_voltage0_raw";

int main() {
  string line;
  while(1) {
    ifstream myfile(fileName, ios::in);

    if (myfile.is_open()) {
      while (getline (myfile,line)) {
        cout << line << '\n';
      }
      myfile.close();
    } else {
      cout << "Unable to open file " << fileName << "\n";
    }
  }

  return 0;
}

 

That's the whole program. After compilation, linking, uploading and setting the executable flag, here's what it looks like in the terminal:

 

image

 

The value changes when moving the potentiometer wiper.

Parents Comment
  • in reply to Jan Cumps

    Thanks for the reference.

    It's a bit sad really - this processor should be much much faster than a CortexM4 with a 180MHz clock but all this software bloat will probably make it chronically slow - it certainly makes setting up the hardware chronically obscure. On an STM32F4xxx once you've set up the DMA it takes no processor instructions at all to get data from an ADC into a circular buffer. This might be the case with the SAMA5 but of course it isn't possible to tell unless you start looking at the driver source code.

    What do you plan ultimately to do with the ADC ?

     

     

    MK

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