在设置mem=30M后 free -m 发现内存的total size也少了2m
感觉这个应该不是最优解

cat /proc/iomem

01c00000-01c0002f : 1c00000.sram-controller
01c02000-01c02fff : 1c02000.dma-controller
01c05000-01c05fff : 1c05000.spi
01c0c000-01c0cfff : 1c0c000.lcd-controller
01c0f000-01c0ffff : 1c0f000.mmc
01c13000-01c133ff : usb@1c13000
01c13000-01c133ff : musb-hdrc.1.auto
01c13400-01c1340f : 1c13400.phy
01c20000-01c203ff : clock@1c20000
01c20800-01c20bff : 1c20800.pinctrl
01c23400-01c237ff : 1c23400.lradc
01c23c00-01c23fff : 1c23c00.codec
01c25000-01c2501f : serial
01c27000-01c273ff : 1c27000.i2c
01e60000-01e6ffff : 1e60000.display-backend
80000000-81ffffff : System RAM
80008000-807fffff : Kernel code
80900000-8096c34b : Kernel data
#

修改前的，看起来reserve是有的，等再找找问题

移植成功
以下是制作ubuntu20.04的rootfs的方法

Requirements

1. An x86_64 machine with Ubuntu or another Linux distribution installed.

2. debootstrap tool.

3. Internet connection.

4. Basic knowledge of using the terminal.

Steps to Create Ubuntu 20.04 Rootfs for ARMhf

1. Install Required Tools

First, ensure that debootstrap and qemu-user-static are installed. qemu-user-static allows you to run ARM binaries on your x86_64 machine.

sudo apt update
sudo apt install debootstrap qemu-user-static

2. Create a Directory for the Rootfs

Create a directory where the root filesystem will be built.

mkdir -p ~/ubuntu-armhf-rootfs

3. Run Debootstrap

Use debootstrap to create the root filesystem. Specify the architecture (armhf), the Ubuntu release (focal), and the target directory.

sudo debootstrap --arch=armhf --foreign focal ./ubuntu-armhf-rootfs https://mirrors.bfsu.edu.cn/ubuntu-ports/

4. Copy QEMU Binary

Copy the qemu-arm-static binary into the usr/bin directory of the new rootfs to enable emulation.

sudo cp /usr/bin/qemu-arm-static ./ubuntu-armhf-rootfs/usr/bin/

5. Chroot into the New Rootfs

Change root into the new root filesystem to complete the second stage of debootstrap.

sudo chroot ./ubuntu-armhf-rootfs

6. Complete Debootstrap Second Stage

Inside the chroot environment, run the second stage of debootstrap.

/debootstrap/debootstrap --second-stage

7. Configure the Rootfs

Now configure the basic settings of your new root filesystem.

• Set the hostname:

echo "ubuntu-armhf" > /etc/hostname

• Set up the hosts file:

cat <<EOL > /etc/hosts
127.0.0.1   localhost
127.0.1.1   ubuntu-armhf
EOL

• Create fstab:

cat <<EOL > /etc/fstab
proc            /proc           proc    defaults        0       0
sysfs           /sys            sysfs   defaults        0       0
devpts          /dev/pts        devpts  gid=5,mode=620  0       0
tmpfs           /run            tmpfs   defaults        0       0
tmpfs           /run/lock       tmpfs   nodev,nosuid,noexec 0   0
EOL

• Set up networking:

cat <<EOL > /etc/network/interfaces
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet dhcp
EOL

• Set the root password:

passwd

• Create a user:

adduser ubuntu
usermod -aG sudo ubuntu

• Install essential packages:

apt update
apt install sudo nano ssh

8. Exit the Chroot

Exit the chroot environment.

exit

9. Clean Up

Remove the qemu-arm-static binary from the rootfs.

sudo rm ./ubuntu-armhf-rootfs/usr/bin/qemu-arm-static

10. Package the Rootfs

Finally, create a tarball of the root filesystem.

sudo tar -czvf ubuntu-20.04-armhf-rootfs.tar.gz -C ./ubuntu-armhf-rootfs .

在移植完后会发现会有readonly fs的问题，其实就是挂载的时候没给rw
bootargs改为

setenv bootargs console=ttyS0,115200 earlyprintk root=/dev/mmcblk0p2 rootwait rw panic=10

就一切正常了

@qlOvQlp
大佬的hdk能开源上来看一下吗？😀😀

太强了，所以sdk有大佬开源吗😀😀