Emulating Cortex A72

Introduction

This document provides a step-by-step guide on how to emulate Cortex A72 using a dietpi image. Please note that this is not intended for production. Use at your own risk.

Prerequisites

• A Linux or macOS (I haven’t tried this on MacOS) system
• wget to download the dietpi image
• p7zip to decompress the image
• fdisk to determine the starting sector number
• kpartx to create loop devices
• nano or any other text editor of your choice to edit the fstab file

Preparation

Create a Project directory

Create a directory to store the project files:

$ mkdir rpi_image
$ cd rpi_image

Download and decompress the Debian RasPi4 image

Download the Debian RasPi4 image and decompress it:

$ wget https://dietpi.com/downloads/images/DietPi_RPi-ARMv8-Bookworm.7z
$ 7za x DietPi_RPi-ARMv8-Bookworm.7z

Mount partitions inside the image

Use kpartx to create loop devices :

$ sudo kpartx -a -v DietPi_RPi-ARMv8-Bookworm.img
add map loop0p1 (254:0): 0 262144 linear 7:0 2048
add map loop0p2 (254:1): 0 1832960 linear 7:0 264192

Mount them like this:

$ sudo mkdir /mnt/dietpi
$ sudo mount /dev/mapper/loop0p2 /mnt/dietpi
$ sudo mount /dev/mapper/loop0p1 /mnt/dietpi/boot

Copy the kernel and dtb from boot

Copy the kernel to wherever you created your rpi_image folder

$ cp /mnt/dietpi/boot/kernel8.img ~/rpi_image/
$ cp /mnt/dietpi/boot/bcm2710-rpi-3-b-plus.dtb ~/rpi_image/

Unmount the image

$ sudo umount /mnt/dietpi/boot
$ sudo umount /mnt/dietpi

Resize the image

You can use gparted to resize, first you need to create a loop device.

$ sudo losetup /dev/loop10 DietPi_RPi-ARMv8-Bookworm.img
$ gparted /dev/loop10

Start qemu

qemu-system-aarch64 \
    -machine raspi3b \
    -cpu cortex-a72 \
    -dtb /home/<username>/rpi_image/bcm2710-rpi-3-b-plus.dtb \
    -m 1G \
    -smp 4 \
    -kernel /home/<username>/rpi_image/kernel8.img \
    -sd /home/<username>/rpi_image/DietPi_RPi-ARMv8-Bookworm.img \
    -append "rw earlyprintk loglevel=8 console=ttyAMA0,115200 dwc_otg.lpm_enable=0 root=/dev/mmcblk0p2 rootdelay=1 modules-load=dwc2,g_ether" \
    -device usb-net,netdev=eth0 \
    -netdev user,id=eth0,net=42.42.42.0/24,hostfwd=tcp::2222-:22 \
    -device usb-kbd \