Work Flow

This article is about the second step and later below. Note that the first step should be completed before reading this article.

Prepare boot files with ramdisk based rootfs distributed by Xilinx according to the previous article.
Setup SD card
1. Modify device tree
2. Create uEnv.txt
3. Create partitions on SD card
4. Copy files to SD card
Setting up Ubuntu 16.04 on Linux running with ramdisk (See also Ref.)
My configuration

Ref. Petalinux 2017.2 Ubuntu RFS on zynq timed out waiting for device

Setup SD card

Modify device tree

Modify bootargs in system-top.dts as follows,

system-top.dts

bootargs = "earlycon root=/dev/mmcblk0p2 rootfstype=ext4 rw rootwait";

Here, we assume /dev/mmcblk0p2 is the drive of rootfs formatted as ext4.
Note that the devicetree.dtb created in the previous step is used in the later steps. It may be better that the device tree blob is created with different name, e.g. devicetree_ubuntu.dtb.

$ dtc -I dts -O dtb -o devicetree_ubuntu.dtb system-top.dts

Create uEnv.txt

u-boot, which built in the previous article, loads Linux kernel basically according to the command list embedded in the binary. (The command sequence is found in include/configs/zynq-common.h) But if uEnv.txt was found in the boot disk, the command listed in the file is preemptively executed.

uEnv.txt

uenvcmd=fatload mmc 0 0x2080000 uImage && fatload mmc 0 0x2000000 devicetree_ubuntu.dtb && bootm 0x02080000 - 0x2000000

The commands load kernel image and devicetree_ubuntu.dtb to 0x2080000 and 0x2000000 respectively, and boot them without specifying the ramdisk address. (See - is in the bootm argument instead of the ramdisk address) By the way, the addresses are from the hard coded boot commands found in zynq-common.h.

Create partitions on SD card

In my Ubuntu 16.04 installed on x64 PC, SD card is found as /dev/sdk.

$ fdisk /dev/sdk

Following two partitions are to be created on a SD card.
1 First partition (1024MB FAT32)
2. Second partition (all remained, EXT4)

The first one is for boot drive, and the second one is for the Ubuntu rootfs. Of course, the capacity of the SD card should be large enough to enjoy Ubuntu 16.04.
Then, two partitions, /dev/sdk1 and /dev/sdk2, are to be formatted as:

$ sudo mkfs.vfat -F 32 /dev/sdk1
$ sudo mkfs.ext4 /dev/sdk2

Copy files to SD card

Now, make mount points, and mount two partitions onto them.

$ mkdir sd_fat32
$ mkdir sd_ext4
$ sudo mount /dev/sdk1 sd_fat32
$ sudo mount /dev/sdk2 sd_ext4

Here sd_fat32 is the first one, sd_ext4 is the second one.
Download and copy Ubuntu rootfs to sd_ext4.

$ wget http://cdimage.ubuntu.com/ubuntu-base/releases/16.04.2/release/ubuntu-base-16.04.3-base-armhf.tar.gz
$ sudo tar zxvf ubuntu-base-16.04.3-base-armhf.tar.gz -C sd_ext4

Copy followings, created previously, to sd_fat32

boot.bin
devicetree.dtb
uramdisk.image.gz
uImage

At this time, uEnv.txt and devicetree_ubuntu.dtb should not be copied, because rootfs of Ubuntu does not work properly; it stalls during boot.

Unmount partitions.

$ sudo umount sd_fat32
$ sudo umount sd_ext4

Remove SD card and insert it to ZYBO Z7-20.

Setting up Ubuntu 16.04 on Linux running with ramdisk

This section is almost the same as in the article. Here, the detailed setup steps are presented that the article does not show.
Boot ZYBO Z7-20 with the SD card created above. The Linux kernel boots with ramdisk rootfs.
First, setup the network interface.

$ ifconfig lo up
$ ifconfig eth0 up
$ ifconfig eth0 192.168.100.10

The network address is for my private network, replace it to yours.
Create mount point rootfs, and mount /dev/mmcblk0p2 the partition of the Ubuntu rootfs.

$ mkdir rootfs
$ mount /dev/mmcblk0p2 /rootfs

On chroot session, create a user zynq and change the password for root.

$ chroot /rootfs adduser zynq
$ chroot /rootfs passwd root

To retrieve required apps using apt, nameserver should be specified in resolv.conf.

$ route add default gw 192.168.100.1
$ echo "nameserver 192.168.100.1" >> /rootfs/etc/resolv.conf

Note that /rootfs/etc/resolv.conf is not /etc/resolv.conf.
Install required packages.

$ chroot /rootfs apt update
$ chroot /rootfs apt upgrade
$chroot /rootfs apt install sudo vim nano net-tools iproute2 iputils-ping ifupdown openssh-client openssh-server -y

Make getty aware of ttyPS0, our serial console.

$ chroot /rootfs ln -s /lib/systemd/system/getty@.service /etc/sys
$ temd/system/getty.target.wants/getty@ttyPS0.service
$ echo "ttyPS0" >> /rootfs/etc/securetty

To make final modification on boot drive, mount it onto /mnt.

$ mount /dev/mmcblk0p1 /mnt

From PCs in the network, copy uEnv.txt and devicetree_ubuntu.dtb to the boot drive of the ZYBO Z7-20.

$ scp uEnv.txt 192.168.100.10:/mnt/uEnv.txt
$ scp devicetree_ubuntu.dtb 192.168.100.10:/mnt/devicetree_ubuntu.dtb

Reboot ZYBO Z7-20. Then Ubuntu starts.

My configuration

Network

Login as root, and modify /etc/network/interfaces as follows.

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet dhcp

Insert followings to /etc/hosts

127.0.0.1 localhost
127.0.1.1 localhost.localdomain

Add zynq to sudoser

usermod -G sudo zynq

Install Apps

gcc
g++
kmod
software-properties-common
git

Device Drivers

Before building Linux kernel,

$ make menuconfig

Enabled drivers.

Device Drivers -> Character devices -> Serial Drivers -> Xilinx uartlite serial port support (using uartlite core in PL)

Disabled drivers.

Device Drivers -> GPIO Support -> Memory mapped GPIO drivers -> Xilinx GPIO support (using my original gpio driver)

Auto-mount Description

Modify fstab as,

/dev/mmcblk0p1 /mnt auto defaults 0 0

GLIBCXX_3.4.22-25

sudo add-apt-repository ppa:ubuntu-toolchain-r/test
sudo apt update
sudo apt upgrade