Wes Aday’s Weblog

EMX – SD card reader June 2, 2010

This is the first real use that I came up with for the EMX board and it would appear that many people have questions regarding the SD card reader capability of the EMX. An SD card would be a quick and easy way to increase the available memory for this primarily embedded system. You might need to save or read text files or log your application to help debug it, updating your application in the field, or other uses.

Create a new project in Visual Studio 2008. Use the Visual C#->Micro Framework->Window Application project template, give the project a meaningful name and click OK.  One thing that I do not like about the template is that the Program.cs file contains the Main method and the window definition. I prefer to separate the functionality but if you want to leave it alone feel free. The only thing that you really need in your Main method is:

Program myApplication = new Program();// Start the application
myApplication.Run(new MainWindow());

I delete the rest of the stuff. Now to the MainWindow. I add a new class called MainWindow to the project. The MainWindow must inherit from Window. Add these using statements:

The first field sets up a PersistentStorage object for out SD card. The second line sets up a port to provide us an interrupt when the SD card is insert and removed. In this case we are going to use IO36, with a glitch filter, using a pull up resistor on the input and finally we want a notification for high and low transitions. If you look closely at the development board, there is a double row of headers down near the lower left side of the board with one side labeled JP1. The sixth pin down from the top is labeled SD Detect and that line is tied to the switch in the SD card connector. By itself it doesn’t do anything, you have to tie that line to an input for the processor. I chose IO36 which is conveniently located right next door to the SD Detect line.  You will need to run a jumper wire from SD Detect to whatever IO line you want to use.  Be very careful!

Width = SystemMetrics.ScreenWidth;
Height = SystemMetrics.ScreenHeight;
Background = new SolidColorBrush(0x000000);

_sdDetect.OnInterrupt += OnSdInterrupt;

private void OnSdInterrupt(uint data1, uint data2, DateTime time)
{
     if (data2 == 0)
     {
          _sdcard = new PersistentStorage("SD");
          _sdcard.MountFileSystem();
     }
     else
     {
          if (_sdcard != null)
          {
              _sdcard.UnmountFileSystem();
          }
     }
}


private void GetFiles()
{
     if (!VolumeInfo.GetVolumes()[0].IsFormatted)
     {
           return;
     }

     string[] files = Directory.GetFiles(VolumeInfo.GetVolumes()[0].RootDirectory);
     foreach (string s in files)
     {
            Debug.Print(s);
     }
}