# Build Kernel

ODROID Linux kernel cross compile

## Package requirement
In order to build Linux kernel, you need to install developement packages required.

```Bash
sudo apt install git build-essential bc flex bison libssl-dev libncurses-dev
```

## Get compiler
For build kernel, you must get cross-compiler, and set some environment values.

| Board                    | Branch          | Cross-compiler                                                                                                                                       |
|--------------------------|-----------------|------------------------------------------------------------------------------------------------------------------------------------------------------|
| ODROID-C4/HC4/N2/N2L/N2+ | odroidg12-4.9.y | [](https://releases.linaro.org/components/toolchain/binaries/7.4-2019.02/aarch64-linux-gnu/gcc-linaro-7.4.1-2019.02-x86_64_aarch64-linux-gnu.tar.xz) |
| ODROID-M1                | odroidm1-4.19.y | [](https://releases.linaro.org/components/toolchain/binaries/7.4-2019.02/aarch64-linux-gnu/gcc-linaro-7.4.1-2019.02-x86_64_aarch64-linux-gnu.tar.xz) |
| ODROID-M1S/M2            | odroidm1-5.10.y | [](https://releases.linaro.org/components/toolchain/binaries/7.4-2019.02/aarch64-linux-gnu/gcc-linaro-7.4.1-2019.02-x86_64_aarch64-linux-gnu.tar.xz) |

```Bash
tar Jxvf gcc-linaro-7.4.1-2019.02-x86_64_aarch64-linux-gnu.tar.xz

export ARCH=arm64
export CROSS_COMPILE=aarch64-linux-gnu-
export PATH=/toolchain/path/gcc-linaro-7.4.1-2019.02-x86_64_aarch64-linux-gnu/bin/:$PATH
```

## Connect odroid and mount
ODROID, which uses an external eMMC, connects to a PC using an [eMMC Writer](https://www.hardkernel.com/shop/usb3-0-emmc-module-writer-2/).

For embedded eMMC like M1S/M2, there are two ways to connect to a PC.

### Use sd card
First, burn below image to sd card.

| Board | Image                                                                         |
|-------|-------------------------------------------------------------------------------|
| M1S   | [](https://dn.odroid.com/RK3566/ODROID-M1S/Installer/ODROID-M1S_EMMC2UMS.img) |
| M2    | [](https://dn.odroid.com/RK3588S2/ODROID-M2/Installer/ODROID-M2_EMMC2UMS.img) |


And boot ODROID, (If M2, set boot switch to Micro SD before boot ODROID), Then connect odroid to your PC using a USB cable.

### Use usb to uart board
Connect [USB-UART Module](https://www.hardkernel.com/shop/usb-uart-2-module-kit-copy/) to pc and ODROID.

Then, connect to ODROID serial using a terminal emulator such as minicom.

| Board            | Baud rate   |
|------------------|-------------|
| M1/M1S/M2        | 1500000 8N1 |
| Except M1/M1S/M2 | 115200 8N1  |

After booting the board, quickly press Ctrl+C to stop booting on u-boot.

```Plain text
...
...
  aclk_perimid 300000 KHz
  hclk_perimid 150000 KHz
  pclk_pmu 100000 KHz
Net:   No ethernet found.
Hit key to stop autoboot('CTRL+C'):  0
=> <INTERRUPT>
=> <INTERRUPT>
=> <INTERRUPT>
=> 
```

Use `ums` command, you can connect ODROID's eMMC as storage.

```Plain Text
=> ums mmc 0
UMS: LUN 0, dev 0, hwpart 0, sector 0x0, count 0x747c000
/
```

If you want stop, just press Ctrl+C, and enter reset for reboot board.
```Plain Text
=> ums mmc 0
UMS: LUN 0, dev 0, hwpart 0, sector 0x0, count 0x747c000
CTRL+C - Operation aborted
=> reset
... Reboot start ...
```


## Set kernel config
One way is to copy the config file from the ODROID board.

```Bash
# In linux kernel source
cp /path/to/mounted/boot/partion/config-{kernel version}-odroid-arm64 .config
```


## Get source

You can get kernel source code from Hardkernel's github

[https://github.com/hardkernel/linux](https://github.com/hardkernel/linux)

In ODROID, you can get branch name use below command:
```Bash
uname -r | awk -F'.' '{print "odroid-" $1 "." $2 ".y"}'
```

| Board                    | Branch          |
|--------------------------|-----------------|
| ODROID-C4/HC4/N2/N2L/N2+ | odroidg12-4.9.y |
| ODROID-M1                | odroidm1-4.19.y |
| ODROID-M1S/M2            | odroidm1-5.10.y |


Clone kernel source from github
```Bash
git clone --depth 1 https://github.com/tobetter/linux -b {branch_name}
```


## Build kernel
You have to tweak a couple of things once in order to let the package `flash-kernel` install your custom kernel properly.
```Bash
cp /boot/config-$(uname -r) .config
sed -i "s/.*CONFIG_LOCALVERSION_AUTO.*/CONFIG_LOCALVERSION_AUTO=y/g" .config
echo "-odroid-arm64" > .scmversion
```

Then. start build kernel
```Bash
make oldconfig
make
```
Kernel builds take a lot of time.
Use `-j` option in `make` command, Make `make` use multicore.




## Install kernel binary
After the build, three main results are generated:
- Kernel image
- Kernel modules
- Device tree binary(dtb), overlay files

In ODROID storage has multiple partitions.
There are usually uboot, boot, and rootfs partitions.

The Kernel image and dtb files are stored in ODROID's boot partition,
and The kernel modules are stored in /usr/lib/modules directory in root partition.

First, you must mount boot and root partitions.
If you use ubuntu-desktop, it will usually be mounted automatically.

For install kernel, you must set some environment variables.
```Bash
export ARCH=arm64
export INSTALL_PATH=/mounted/BOOT/partition/path
export INSTALL_MOD_PATH=/mounted/root/partition/path
```

Maybe you need sudo permission, use `sudo -E`, you can keep environment variable values.

```Bash
# kernel install
sudo -E make install

# dtbs install
sudo -E make dtbs_install

# modules install
sudo -E make modules_install
```


### Change kernel
You can see installed kernel list, use command `linux-version list`.

If you want change kernel version, use `flash-kernel`.
```Bash
sudo flash-kernel --force 5.9.0-odroid-arm64
```

<seealso>
    <category ref="external">
        <a href="https://github.com/hardkernel/linux">Official kernel source</a>
        <a href="https://github.com/tobetter/linux">Tobetter's kernel source</a>
        <a href="https://docs.linuxfactory.or.kr/guides/compile_kernel.html">Build odroid kernel</a>
    </category>
</seealso>