A Mutable Log

A blog by Devendra Tewari

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Write Ubuntu image file to SD card on Windows

I use an 8 GB class 4 SD Card to run the Ubuntu distribution for OMAP4 on a PandaBoard. This post details the procedure I use to prepare the SD Card on Windows.

Download and write Ubuntu image

You’ll need the following tools

  1. 7-zip or other decompressor that can extract gzipped file (extension gz).
  2. Win32 Disk Imager to write the img file to the SD Card.
  3. A laptop with SD Card reader, or an external USB SD Card reader.

Here’s the procedure to prepare the SD Card

  1. Download Ubuntu gzipped image file for OMAP4 boards
  2. Extract img file using 7-zip
  3. Insert SD Card into reader
  4. Execute Win32DiskImager.exe - it requests admin privileges on Windows 7
  5. Select the image file extracted in step 2
  6. Select the device that corresponds to the SD Card reader
  7. Write the image file - this will take a while
  8. Eject the SD Card

Backup or Clone SD Card

Win32 Disk Imager can also be used to read an SD Card. You can write the image file to the same or another SD Card.

Restore SD Card to Original State

The SD Card will be partitioned after the procedure above. To restore it to its original state i.e. create a single partition with all the available space, you’ll need to use the GParted Partition Editor on a Linux box, or from a live CD. Windows 8 Disk Management tool may also work.

Patch for version 0.3 of Win32 Disk Imager

Version 0.3 binary of Win32 Disk Imager has a bug in a call to Win32 SetFilePointer function. The image read is about half the size of my 8 GB SD Card. I built it from source using QT Creator after patching the following two functions in disk.cpp

char *readSectorDataFromHandle(HANDLE handle, unsigned long long startsector, unsigned long long numsectors, unsigned long long sectorsize)
{
    unsigned long bytesread;
    char *data = new char[sectorsize * numsectors];
    LARGE_INTEGER li;
    li.QuadPart = startsector * sectorsize;
    SetFilePointer(handle, li.LowPart, &li.HighPart, FILE_BEGIN);
    if (!ReadFile(handle, data, sectorsize * numsectors, &bytesread, NULL))
    {
        char *errormessage=NULL;
        FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_ALLOCATE_BUFFER, NULL, GetLastError(), 0, (LPSTR)&errormessage, 0, NULL);
        QMessageBox::critical(NULL, "Read Error", QString("An error occurred when attempting to read data from handle.\nError %1: %2").arg(GetLastError()).arg(errormessage));
        LocalFree(errormessage);
        delete data;
        data = NULL;
    }
    return data;
}

bool writeSectorDataToHandle(HANDLE handle, char *data, unsigned long long startsector, unsigned long long numsectors, unsigned long long sectorsize)
{
    unsigned long byteswritten;
    BOOL bResult;
    LARGE_INTEGER li;
    li.QuadPart = startsector * sectorsize;
    SetFilePointer(handle, li.LowPart, &li.HighPart, FILE_BEGIN);
    bResult = WriteFile(handle, data, sectorsize * numsectors, &byteswritten, NULL);
    if (!bResult)
    {
        char *errormessage=NULL;
        FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_ALLOCATE_BUFFER, NULL, GetLastError(), 0, (LPSTR)&errormessage, 0, NULL);
        QMessageBox::critical(NULL, "Write Error", QString("An error occurred when attempting to write data from handle.\nError %1: %2").arg(GetLastError()).arg(errormessage));
        LocalFree(errormessage);
    }
    return (bResult == TRUE);
}

That fixes the problem with reading and writing large SD Cards.