Six steps to Building an Embedded Linux System

The first phase of the installation process is to create a new virtual machine running under the VMware Workstation environment and start it up. Follow VMware's easy installation instructions and create a virtual machine with 32 MB of hard drive space. Then we'll show you how to turn it into a small Linux system running LabVIEW.

The CD-ROM that comes with this book is a bootable disk that contains the tools you will need to build your own embedded Linux system. Reboot the virtual machine off of the CD-ROM and follow these six steps . . .

• Step 1. Partion the Virtual Hard Drive — Inside the virtual machine at the Linux command prompt, type the command fdisk /dev/hda to format the virtual disk. You need to create a new primary partition that will take up the whole drive. Select n for a new partition, then p to make it a primary partition. It will be partition number 1 so enter a 1.Now that you have created the partition table you need to write it to disk so type w.

• Step 2. Format the Virtual Hard Drive — After making a partition on the virtual disk you need to format or make a filesystem on your new partition. To make Linux's native ext2 filesystem we'll use the command mke2fs -m 0 /dev/hda1. This command in brief says that we will make an ext2 filesystem on the new partition we just created, /dev/hda1. The mke2fs command automatically detects the space available on the partition. The -m 0 option (zero, not “oh”) means that we are going to use all the space on the disk for ourselves and not reserve any space for the root user of a multi-user system

• Step 3. Mount the target Partition — To mount the hard drive we'll use the command mount followed by which device to mount and where to mount it.
  
  
  # mount /dev/hda1 /mnt
  
  
  
• Step 4. Transfer the Operating System from the CD-ROM — In the /usr directory of the CD-ROM there is a 11 MB file named embeddedlabview.tar.gz that contains everything you need for your first embedded Linux system. The CD-ROM contains some lightweight embedded system tools that do not have all the functionality of the GNU tools you may be used to with a typical Linux or UNIX system but they have more than enough functionality to get the job done.

  In order to decompress and extract your compressed archive you have to use a combination of two commands. The command zcat decompresses our archive and turns it from .tar.gz to a .tar file. To keep from making an intermediary .tar file we will use a UNIX pipe to send the output of the zcat command to the input for the tar command. The tar command extracts the files in the archive into our mounted directory:
  

  
  # zcat /usr/embeddedlabview.tar.gz | (cd /mnt; tar -xvf -)
  
  
  As the archive is extracted to the hard drive you should see a long list of files go by on your screen. When the tar command is finished you can poke around through the contents of the new hard drive. Use the command cd /dirname (e.g., cd /bin) to change directories and the command ls to list their contents. We'll explore the file structure later in the chapter. Right now let's finish up the installation and reboot into your new system.

• Step 5. Install the bootloader — Your virtual hard drive now has a Linux kernel and all the support files it needs to boot. Everything is in place except for the bootloader, a small section of code that is started by the BIOS and loads the operating system. The most popular bootloader for Linux is LILO (LInux LOader). LILO stores its information in the master boot record or MBR of the hard drive. When we issue the following command, LILO will read its configuration file (/etc/lilo.conf) in the /mnt directory and write its information to the MBR of /dev/hda.
  
  
  # lilo -v -C /etc/lilo.conf -r /mnt
  
  
  
• Step 6. Boot up Your New Virtual Embedded System — The system is now bootable. Hit crtl-alt-delete (Linux) or ctrl-alt-ins (Windows) to reboot and remove the CD-ROM from the drive. The (virtual) system should boot directly from the hard drive. After the VMware Workstation machine starts you will see Linux booting up. Once Linux has booted, the system will run a pre-compiled example LabVIEW application. Play with the buttons, explore the menus and you will see that LabVIEW for Linux is just like LabVIEW for any other platform.

So far we've created a virtual embedded system to make it easier to get started developing real embedded systems. As you have seen, developing software using virtual machines is a powerful and efficient way to work. However, because of the way that the virtual machine software works, it is not suitable for demanding real-time applications. For that you will have to move to actual embedded hardware.

• Part 1: Introduction
  
• Part 2: What is LabVIEW?
  
• Part 3: Why use a desktop OS to build an embedded system?
  
• Part 4: Getting to know VMware
  
• Part 5: Six steps to Building an Embedded Linux System
  
• Part 6: Deploying on the hardware
  
• Part 7: Conclusion

 
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