How to run Linux on QEMU ? How do I learn embedded systems programming without the actual hardware ?

How to run Linux on QEMU ? 

How do I learn embedded systems programming without the actual hardware ?

Linux 5.15 on QEMU

Yes you can run learn Embedded Systems without actual hardware.

 

The option is QEMU. QEMU is a emulator. Its free and open-source. It emulates the actual hardware or machine's processor.

 

Example If you want to work or run Linux OS on Raspberry Pi you don't need actual Raspberry pi hardware. The QEMU acts as hardware (i.e emulator).

 

Example you can see source code QEMU for emulating Raspberry Pi 2 & 3.

 

https://github.com/qemu/qemu/blob/master/hw/arm/raspi.c

 

The different peripheral of Raspberry Pi  like I2C, SPI, GPIO etc added here.

https://github.com/qemu/qemu/blob/master/hw/arm/bcm2835_peripherals.c#L383

The base addresses and offset of different peripheral and how they should work are implemented here.

 

Raspberry Pi (BCM2835) GPIO Controller :

 

https://github.com/qemu/qemu/blob/master/hw/gpio/bcm2835_gpio.c 

BCM2835 (Raspberry Pi / Pi 2) Aux block (mini UART and SPI):

 

https://github.com/qemu/qemu/blob/master/hw/char/bcm2835_aux.c

 

These are not device driver. Actual implementation of how controller should work.

And similarly "MCIMX6UL_EVK Board System" emulation is done here:

https://github.com/qemu/qemu/blob/master/hw/arm/mcimx6ul-evk.c

If you are an android developer you may know Android emulator to run the app and test. Instead of using actual Android mobile (Hardware) you will use emulator.

 

Similarly QEMU, but it has different operating mode.

 

If you want to run only application then you can use User-mode emulation.

If you want to customize OS source code and validate then you need to use system emulation mode.

 

In this article I will explain how to get source code of QEMU and build ?

How to emulate the device ? How to run Linux Kernel Image ?

Create a folder demo or anything.

$ mkdir demo

 

The Yocto project releases are listed here:

http://downloads.yoctoproject.org/releases/yocto/

 

The current Yocto release is 4.0, so we will install that into our host system.

 

$  wget http://downloads.yoctoproject.org/releases/yocto/yocto-4.0/poky-00cfdde791a0176c134f31e5a09eff725e75b905.tar.bz2

 

$ tar -xvzf  poky-00cfdde791a0176c134f31e5a09eff725e75b905.tar.bz2

 

$ cd poky

 

 

Now run the "OE Build Environment Setup Script" to setup the environment.

In your case initially there will not be "build" folder as seen in above image. Once below command is given, it will create a build folder for you.

$ source oe-init-build-env

 

 Observe the terminal, now you are in "build" folder automatically.

If you don't want to use default "build" folder and you want give a name then you can use below command:

$ source oe-init-build-env <name to folder>

$ source oe-init-build-env qemuarm_build

Observe the image. Now you are in "qemuarm_build" folder instead of default "build" folder. (Click on the image to enlarge the image.)

It will automatically create a folder "conf" and files under this.

The files are as below:

└── conf
    ├── bblayers.conf
    ├── local.conf
    └── templateconf.cfg

 

In the bblayers.conf file, the list of meta-* folders path will be automatically added by the script.

local.conf:

This file is your local configuration file and is where all local user settings are placed. The comments in this file give some guide to the options a new user to the system might want to change but pretty much any configuration option can be set in this file. More adventurous users can look at local.conf.sample.extended which contains other examples of configuration which can be placed in this file but new users likely won't need any of them initially.
Lines starting with the '#' character are commented out and in some cases the default values are provided as comments to show people example syntax. Enabling the option is a question of removing the # character and making any change to the variable as required.

By default MACHINE variable  is x86-64

MACHINE ??= "qemux86-64"

As we need to emulate ARM device select the machine as "qemuarm"

MACHINE ?= "qemuarm"

Remove the character '#' to uncomment the line.

Now run the below command to build the Linux image and Root file system :

$ bitbake core-image-minimal 

To run the QEMU different python scripts are provided in the path:

poky/scripts

Once image build is success, run "runqemu" command boot the Linux image on ARM emulated device:

$ runqemu qemuarm core-image-minimal