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Building Embedded Linux - Full Custom

Building the Kernel

Summary

Here we build a kernel for the DE10-Nano from scratch.

Steps

Library dependencies

The following packages are needed for compiling the kernel:

sudo apt-get install libncurses-dev flex bison openssl libssl-dev dkms libelf-dev libudev-dev libpci-dev libiberty-dev libmpc-dev libgmp3-dev autoconf bc

Download the Kernel

Altera has their own fork of the kernel. You can clone the altera linux repository:

cd $DEWD
git clone https://github.com/altera-opensource/linux-socfpga.git

List the branches with git branch -a and checkout the one you want to use. We chose to use the latest available at the time of writing. What's the point of using an ancient kernel if you're going to all this trouble?

cd linux-socfpga

# View the list of available branches.
git branch -a

# Use the branch you prefer.
git checkout socfpga-5.12

Configure the Kernel

Initialize the configuration for the DE10-Nano:

make ARCH=arm socfpga_defconfig

Now open the kernel configuration window:

make ARCH=arm menuconfig

There are a few adjustments we want to make. But before that, let's understand a little bit about how to flash the FPGA on your DE10-Nano.

Primer on Flashing FPGA

There are a few ways to flash your FPGA design. The traditional way is to just connect to the USB blaster interface and just flash it away. However, with the ARM HPS on our SoC, we have a couple of other ways as well:

  1. Flash from U-Boot on boot - U-Boot has the ability to flash the FPGA design using some built-in commands. We will visit how to do this when we're building U-Boot.
  2. Flash from Linux while running - I think this is one of the big benefits of having an HPS. We can flash our hardware design directly from Linux without even rebooting the device.

To be able to do this, we need to enable the Overlay filesystem support and Userspace-driven configuration filesystem in the kernel. If you don't intend to flash your FPGA from linux then feel free to skip these.

NOTE - If you don't need these 2 options, you can just use the mainstream linux source to build your kernel instead of the altera-opensource version. Just clone the repository at github.com/torvalds/linux.

Kernel Options

Do not append version

Under General setup and uncheck Automatically append version information to the version string. This makes it easier to test different versions of the drivers. Better to keep it enabled in production though.

Enable Overlay filesystem support

Under File systems, enable Overlay filesystem support and all the options under it:

Enable CONFIGFS

This should be enabled already, but if not, do enable it:

Feel free to look through the other options and when done, press the right-arrow key until Exit is highlighted and press enter. Keep exiting until you get a window that asks if you want to save config. Choose yes and that will exit you out of the utility.

(Optional) Enable options for WIFI

You can set up the necessary options needed for WIFI as explained here. This can be done later as well.

Build the Kernel image

Now we can finally build the kernel image. Use the following command to create a kernel image called zImage:

make ARCH=arm LOCALVERSION=zImage -j 24

If it makes any complaints about bc not found or flex not found, install that utility using sudo apt install <library>.

The kernel gets compiled in about 5-10 mins on my Virtualbox Debian, but YMMV.

Once the compilation is complete, you now have a compressed Linux kernel image.

References

Building embedded linux for the Terasic DE10-Nano - A large part of this page has been taken from here.

Stackoverflow - Cannot mount configfs - This page explains why you cannot see the device tree overlay.

Next | RootFS - Choose one
Back | Building the Universal Bootloader (U-Boot)

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