Creating the Image Build Script

Before we start

I decided to use odroidc1image.sh as a template and copied it to tinkerimage.sh
This chapter will describe which parts need to be adjusted and for what reason.
For the complete template script see http://github.com/volumio/Build/scripts/odroidc1image.sh
The resulting tinkerimage.sh can be found here
The parts of the C1 template which are not mentioned here are considered generic and unlikely candidates for changes.

Creating the image file

This part is self-explanatory, the file needs the name of the new image.

IMG_FILE="Volumio${VERSION}-${BUILDDATE}-odroidc1.img"

becomes

IMG_FILE="Volumio${VERSION}-${BUILDDATE}-tinkerboard.img"

Partitioning

The size of the file is the same for most devices (currently 2.8GB), it will get three partitions

a boot partition (fat32) of approx. 60-64MB
an image partition (ext4) of approx. 2.3GB
a data partition (ext4) with the rest (which will get resized on first boot to the complete size of the card the image was flashed to)

The boot partition's offset is the first one from the device-specific adaption and needs to be chosen carefully. It depends on the size of the bootloader(s).
For the C1 and Tinkerboard the bootloaders fit into the first block, so the partitioning details remain unchanged.

Preparing for the tinkerboard rockchip kernel/ platform files

This part is also self-explanatory, we only need to change the names of the platform repo and tar file.
We use the name platform-asus and tinkerboard.tar.xz from the kernel build process.

if [ -d platform-asus ]
then
    echo "Platform folder already exists - keeping it"
    # if you really want to re-clone from the repo, then delete the platform-asus folder
    # that will refresh all the asus platforms, see below
else
    echo "Clone asus files from repo"
    git clone https://github.com/volumio/platform-asus.git platform-asus
    echo "Unpack the Tinkerboard platform files"
    cd platform-asus
    tar xfJ tinkerboard.tar.xz
    cd ..
fi

This won't work yet, as we have not pushed the platform files to the volumio repo.
To be able to use the script anyway, go to the root folder from your build repo copy and type

mkdir platform-asus
cd platform-asus
cp $DESTDIR/tinkerboard.tar.xz .    (where $DESTDIR is the one you used in Chapter "Saving Files to the Platform folder")
tar xvfJ tinkerboard.tar.xz

Copying the bootloaders

This is the second device-specific adaption of the script, together with the boot partition offset, this us usually the most critical part of customizing a template. This part, when not done properly, will render the image unbootable.

C1 version

echo "Copying the bootloader"
dd if=platform-odroid/odroidc1/uboot/bl1.bin.hardkernel of=${LOOP_DEV} bs=1 count=442
dd if=platform-odroid/odroidc1/uboot/bl1.bin.hardkernel of=${LOOP_DEV} bs=512 skip=1 seek=1
dd if=platform-odroid/odroidc1/uboot/u-boot.bin of=${LOOP_DEV} seek=64
sync

Tinkerboard

From compiling u-boot, we already know, that there is an image (only one) we need to copy to a certain position at the beginning of the image, so the C1 part gets replaced by

echo "Copying the bootloader"
dd if=platform-asus/tinkerboard/u-boot/u-boot.img of=${LOOP_DEV} seek=64 conv=notrunc
sync

As said, this is device-specific and not always that simple, the following is an example of the Odroid XU4

echo "Copying the bootloader and trustzone software"
dd iflag=dsync oflag=dsync if=platform-odroid/odroidxu4/uboot/bl1.bin.hardkernel of=${LOOP_DEV} seek=1
dd iflag=dsync oflag=dsync if=platform-odroid/odroidxu4/uboot/bl2.bin.hardkernel of=${LOOP_DEV} seek=31
dd iflag=dsync oflag=dsync if=platform-odroid/odroidxu4/uboot/u-boot.bin.hardkernel of=${LOOP_DEV} seek=63
dd iflag=dsync oflag=dsync if=platform-odroid/odroidxu4/uboot/tzsw.bin.hardkernel of=${LOOP_DEV} seek=719
echo "Erasing u-boot env"
dd iflag=dsync oflag=dsync if=/dev/zero of=${LOOP_DEV} seek=1231 count=32 bs=512
sync

Copying system files, preparing for board configuration

This part is also self-explanatory, it deals with the rootfs, kernel image, dtb, boot configuration, modules and firmware. Just ensure the files are copied to the right locations and it fits the boot configuration you created.

Starting chroot

Again, the part is more or less generic and easy to adapt (2 x script name and 1 x boardname)

chroot /mnt/volumio/rootfs /bin/bash -x <<'EOF'
su -
/tinkerconfig.sh
EOF

#cleanup
rm /mnt/volumio/rootfs/root/init /mnt/volumio/rootfs/tinkerconfig.sh

echo "Unmounting Temp devices"
umount -l /mnt/volumio/rootfs/dev
umount -l /mnt/volumio/rootfs/proc
umount -l /mnt/volumio/rootfs/sys

echo "==> Tinkerboard device installed"


## Creating the Image Build Script (Part 2)
For the config script we use the corresponding __odroidc1config.sh__ as a template.
This chapter will describe which parts need to be adjusted and for what reason.  
For the complete template script see __<http://github.com/volumio/Build/scripts/odroidc1config.sh>__  
The resulting tinkerimage.sh can be found [__here__](http://github.com/volumio/Build/scripts/tinkerconfig.sh)  
The parts of the C1 template which are not mentioned here are considered generic and unlikely candidates for changes.
### Creating fstab
Just change the description in line 1.
This part is standard in most implementations we encountered as most devices boot from mmcblk0, independent of SD or eMMC.
That said, this may call for a future change.  
Newer devices using mainline u-boot and offering boot from emmc and sd are now using different devices.  
This may require the UUID for locating the correct boot device as we do not want to produce separate images for booting from SD or eMMC.  
An example implementation "by_UUID" you will find in the x86 build scripts.
### Adding default sound modules ###
Tinkerboard does not (yet) support i2s devices, so no need to load sound modules.
This may chnage in future releases.
### init script ###
Tinkerboard is still headless, C1 uses a script to initialise the framebuffer at an early stage (C1-init.sh).
In case Tinkerboard needs this, add it to the tinker init script, which was implemented like this:

    echo "#!/bin/sh
    echo 2 > /proc/irq/45/smp_affinity
    " > /usr/local/bin/tinker-init.sh
    chmod +x /usr/local/bin/tinker-init.sh

    echo "#!/bin/sh -e
    /usr/local/bin/tinker-init.sh
    exit 0" > /etc/rc.local
Currently, the init script changes the usb interrupt CPU affinity (from CPU0 to CPU1).  
This was done to avoid possible crackling and dropouts on usb audio.
The script runs when rc.local is called at boot time.  
### Additional packages ###
lirc is installed, but no specific configuration for a remote is present yet.
It defaults to a small remote Hardkernel offers for the C1/C2.
As no framebuffer initialisation is done, package "fbset" is not needed and removed.