Into Embedded – two chapters to look at

The first two chapters of the book Into Embedded have been updated.

There is also a Book Software page where you can download the software for these two chapters.

The software treats, for 32-bit Intel and for ARM, the topic of building a small program that can run without the help of an operating system. This is often referred to as bare metal programming, and I think it can be both rewarding and challenging.

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A bare-metal x86-cross-compiler on Mountain Lion

I wanted to create a bare-metal program for an Intel-x86 processor. The program is used in a chapter called The Bare Metal in the book Into Embedded.

On an Ubuntu Linux host I could use gcc, together with a linker script, to accomplish the task. I could then run the program using Bochs.

On a Mac Mountain Lion host, the above method did not work out of the box, due to ld not being the GNU linker.

In addition, gcc was not GNU gcc either.

I searched the net and found this interesting page by M3 Operating System Development where it was described how to build an i386 cross-compiler. I thought that this could be a way to create a compiler for bare-metal programs with no OS-dependencies – which was desirable since the bare-metal program was to be evolved into an OS by itself.

Problem arose, however, since the pre-installed gcc on my Mac could not build the i386-cross-gcc.

I searched again, and found this eminent page by Solarian Programmer where it is described how to build a GNU gcc compiler.

I downloaded the gcc 4.7.2 sources from the GNU ftp repository.

Then, following the instructions, however leaving out the choice of building a compiler for Fortran and also changing the gcc version from 4.7.1 to gcc 4.7.2, I was able to build a native GNU gcc compiler.

The newly built native gcc could then be set to the default gcc by issuing the command

export PATH=/usr/gcc-4.7.2/bin:$PATH

Then, returning to the instructions for building an i386-cross-gcc, I started with downloading

binutils-2.23.tar.gz

from the GNU binutils repository.

I created a destination directory for the cross compiler, by doing

sudo mkdir /usr/local/i386elfgcc/

The binutils could then be unpacked, configured, and built, using the commands

tar zxvf binutils-2.23.tar.gz
mkdir build-binutils
cd build-binutils/
../binutils-2.23/configure --target=i386-elf --prefix=/usr/local/i386elfgcc
make
sudo make install

I then built gcc, using inspiration also from this OS development wiki, by issuing the commands

tar xvjf gcc-4.7.2.tar.bz2
mkdir build-gcc
cd build-gcc
../gcc-4.7.2/configure --target=i386-elf --prefix=/usr/local/i386elfgcc --with-gnu-as --with-gnu-ld --disable-libssp --enable-languages=c --without-headers
make all-gcc
sudo make install-gcc

After having added /usr/local/i386elfgcc/bin to the PATH environment variable I was able to compile and link a bare metal program.

The program consists of three C-files, which I could compile using the commands

i386-elf-gcc -Wall -c screen_output.c
i386-elf-gcc -c -Wall -DBUILD_X86_FD_TARGET src/bare_metal.c -o obj/bare_metal_x86_fd_target.o
i386-elf-gcc -c -Wall -DBUILD_X86_FD_TARGET src/console.c -o obj/console_x86_fd_target.o

The program could then be linked, using a command where also startup code, written in assembly and assembled using NASM resulting in the object file start_code.o, as

i386-elf-ld -T arch/x86_fd_target/link.ld --oformat=elf32-i386 -melf_i386 arch/x86_fd_target/start_code.o arch/x86_fd_target/screen_output.o -o prog_x86_fd_target.elf obj/console_x86_fd_target.o obj/bare_metal_x86_fd_target.o

Finally, the file prog_x86_fd_target.elf needs to be converted from ELF format to raw binary format. This can be done using the command

i386-elf-objcopy -O binary prog_x86_fd_target.elf prog_x86_fd_target.bin

As a last step, a binary bootable image for a floppy-disc drive can be created, by concatenating a FAT12 boot sector, a defined number of empty FAT12-sectors, and the binary file created by the i386-elf-objcopy command.

The concatenation is done as

cat arch/x86_fd_target/boot.bin arch/x86_fd_target/b_32_512.bin prog_x86_fd_target.bin > arch/x86_fd_target/a.img

The program can now be run, using Bochs, by giving the command

bochs -f arch/x86_fd_target/bochsrc.txt -q

Installing Bochs

Bochs is an x86-emulator that can be installed on different platforms. Here I describe my experiences of installing Bochs on Linux and on MacOS Mountain Lion.

Ubuntu Linux

Installing Bochs on Ubuntu was simple. I did

sudo apt-get install bochs

Then I located the Bochs configuration file. It was found, and copied to the directory where I intended to run Bochs, as

cp /usr/local/share/doc/bochs/bochsrc-sample.txt bochsrc.txt

My goal was to simulate an x86-computer with a floppy-disc unit. Changes were therefore done, in the file bochsrc.txt. The changes can be seen from the diff-command

diff /usr/local/share/doc/bochs/bochsrc-sample.txt bochsrc.txt

as

387c387
< floppya: 1_44=/dev/fd0, status=inserted
---
> #floppya: 1_44=/dev/fd0, status=inserted
392c392
< #floppya: 1_44=a.img, status=inserted, write_protected=1
---
> floppya: 1_44=arch/x86_fd_target/a.img, status=inserted, write_protected=1
474c474
< ata0-master: type=disk, mode=flat, path="30M.sample"
---
> #ata0-master: type=disk, mode=flat, path="30M.sample"
494,495c494,495
< #boot: floppy
< boot: disk
---
> boot: floppy
> #boot: disk

Then I am ready to run Bochs, using the command

bochs -f arch/x86_fd_target/bochsrc.txt -q

resulting in a simulated PC screen, as

bochs hello

Linux

The Bochs project is found at http://bochs.sourceforge.net.

After reading information about the latest release, I navigated to the releases page. I then downloaded release 2.6 in source format, resulting in download of the file

bochs-2.6.tar.gz

I then unpacked the source and navigated to the newly created bochs source directory, as

tar zxvf bochs-2.6.tar.gz
cd bochs-2.6

Then the configure script shall be run. Since I was not root on the machine, I used a prefix to configure, indicating the directory where I wanted Bochs to be installed. The configure command used was

./configure --prefix=/nobackup/local/prog/bochs

Bochs was then built, using the command

make

and installed using the command

make install

Then I located the Bochs configuration file. It was found, and copied to the directory where I intended to run Bochs, as

cp /nobackup/local/prog/bochs/share/doc/bochs/bochsrc-sample.txt arch/x86_fd_target/bochsrc.txt

My goal was to simulate an x86-computer with a floppy-disc unit. Changes were therefore done, in the file bochsrc.txt. The changes can be seen from the diff-command

diff /nobackup/local/prog/bochs/share/doc/bochs/bochsrc-sample.txt arch/x86_fd_target/bochsrc.txt

as

190c190
< cpu: model=core2_penryn_t9600, count=1, ips=50000000, reset_on_triple_fault=1, ignore_bad_msrs=1, msrs="msrs.def"
---
> cpu: count=1, ips=50000000, reset_on_triple_fault=1, ignore_bad_msrs=1, msrs="msrs.def"
415c415
< floppya: 1_44=/dev/fd0, status=inserted
---
> #floppya: 1_44=/dev/fd0, status=inserted
420c420
< #floppya: 1_44=a.img, status=inserted, write_protected=1
---
> floppya: 1_44=arch/x86_fd_target/a.img, status=inserted, write_protected=1
502c502
< ata0-master: type=disk, mode=flat, path="30M.sample"
---
> #ata0-master: type=disk, mode=flat, path="30M.sample"
522,523c522,523
< #boot: floppy
< boot: disk
---
> boot: floppy
> #boot: disk
636c636
< debug: action=ignore, pci=report # report BX_DEBUG from module 'pci'
---
> debug: action=ignore, # pci=report # report BX_DEBUG from module 'pci'

I also added the following changes

export PATH=/nobackup/local/prog/bochs/bin:$PATH
export BXSHARE=/nobackup/local/prog/bochs/share/bochs

to my setup script, where I also set up other environment variables.

Then I am ready to run Bochs, using the command

bochs -f arch/x86_fd_target/bochsrc.txt -q

resulting in a simulated PC screen as shown above.

Mac Mountain Lion

I navigated to the releases page. I then downloaded release 2.6 in source format, resulting in download of the file

bochs-2.6.tar.gz

I then unpacked the source and navigated to the newly created bochs source directory, as

tar zxvf bochs-2.6.tar.gz
cd bochs-2.6

The configure command used was

./configure --with-x11

The –with-x11 indicates that X11 shall be used. For this purpose I had installed XQuartz, as described by Apple in this support note.

Bochs was then built, using the command

make

and installed using the command

sudo make install

I used the same configuration file as described above for Ubuntu, and I could then run Bochs using the command

bochs -f arch/x86_fd_target/bochsrc.txt -q

resulting in a simulated PC screen, as shown above.

Installing QEMU

QEMU is an open source computer emulator. Here I describe how I installed QEMU on Linux and on Mac Mountain Lion.

My goal was to create a simulator for machines with ARM architecture and for machines with x86 architecture.

Updates to this post

  • July 15, 2013 – changed the section on Ubuntu Linux to cover QEMU 1.5.1 instead of QEMU 1.2.0.

Ubuntu Linux

Starting from the QEMU home page I navigated to the download page. From there I downloaded the file

qemu-1.5.1.tar.bz2

I unpacked the file, and navigated to the directory created during the unpacking, using the commands

tar xvjf qemu-1.5.1.tar.bz2
cd qemu-1.5.1

As a preparation, I needed to update my Ubuntu 13.04 installation. It turned out that the following installations were needed:

sudo apt-get install zlib1g-dev
sudo apt-get install libglib2.0
sudo apt-get install autoconf
sudo apt-get install libtool
sudo apt-get install libsdl-console
sudo apt-get install libsdl-console-dev

I could then configure QEMU, using the command

./configure --target-list=i386-softmmu,arm-softmmu,x86_64-softmmu --disable-vnc --enable-sdl

I could then build and install, using

make
sudo make install

I could then use QEMU, for simulation of an ARM computer, e.g. as

qemu-system-arm -M realview-pb-a8 -nographic -kernel prog_arm_rpb_a8.elf

and simulation of an x86 computer, e.g. as

qemu-system-x86_64 -kernel prog_x86_grub_target.elf

Problems encountered – I had some trouble before realizing which packages to add to Ubuntu in order to get QEMU to build. The first thing that happened was that the configure command failed, with

ERROR: zlib check failed
Make sure to have the zlib libs and headers installed.

which, after some searching, led me to install zlib as

sudo apt-get install zlib1g-dev

Then I got a message I recognized from my installation of QEMU on Mac, saying that

ERROR: glib-2.12 required to compile QEMU

which, again after some searching, led to the installation of glib as

sudo apt-get install libglib2.0

Configure was now happy but make was not. The make command gave an error, as

(cd /home/ola/Downloads/qemu-1.5.1/pixman; autoreconf -v --install)
/bin/sh: autoreconf: command not found
make: *** [/home/ola/Downloads/qemu-1.5.1/pixman/configure] Error 127

Trying the command autoreconf, as

ola@ola-Aspire-S3-391:~/Downloads/qemu-1.5.1$ autoreconf
The program 'autoreconf' can be found in the following packages:
* autoconf

led to the installation of autoconf, as

sudo apt-get install autoconf

An error telling me to install libtool then appeared, as

../../lib/autoconf/general.m4:2678: AC_LINK_IFELSE is expanded from...
configure.ac:552: the top level
configure.ac:75: error: possibly undefined macro: AC_PROG_LIBTOOL
If this token and others are legitimate, please use m4_pattern_allow.
See the Autoconf documentation.
autoreconf: /usr/bin/autoconf failed with exit status: 1
make: *** [/home/ola/Downloads/qemu-1.5.1/pixman/configure] Error 1
make: *** Deleting file `/home/ola/Downloads/qemu-1.5.1/pixman/configure'

which, by help from Erik Rull, led me to the installation of libtool, as

sudo apt-get install libtool

Now everything built, and I could also do an installation of QEMU, as

sudo make install

The ARM simulation worked fine, but there was no screen in the x86 simulation. I guessed that I needed also SDL for this purpose, and after the installation of sdl, as

sudo apt-get install libsdl-console
sudo apt-get install libsdl-console-dev

I could see a console, and the long-awaited “Hello, world”-message from my program.

Linux

I downloaded and unpacked QEMU in the same way as described above for Ubuntu Linux.

Then, since I was not root on the machine, I used the configure command

./configure --prefix=/nobackup/local/prog/qemu --target-list=i386-softmmu,arm-softmmu,x86_64-softmmu --disable-vnc

followed by commands for build and installation, as

make
make install

I also added the following changes

export PATH=/nobackup/local/prog/qemu/bin:$PATH

to my setup script, where I also set up other environment variables.

I could then use QEMU, for simulation of an ARM computer, e.g. as

qemu-system-arm -M realview-pb-a8 -nographic -kernel prog_arm_rpb_a8.bin

Mac Mountain Lion

I downloaded and unpacked QEMU 1.2.0 in the same way as described above for Ubuntu Linux.

Then, based on information from Ruben Schade, I used the configure command

./configure --enable-cocoa --target-list=i386-softmmu,arm-softmmu,x86_64-softmmu --disable-vnc

This command generated an error, telling me that “glib-2.12” was “required to compile QEMU”. I searched for this error, and after having read at this MacPorts-related page, I ended up doing

sudo port install glib-2.12
sudo port selfupdate
sudo port upgrade outdated

which, as a result, made it possible to redo the configure command as decribed above.

I then built QEMU, which succeeded but with several warnings, and installed it, using

make
sudo make install

I could now use QEMU, for simulation of an ARM computer, e.g. as

qemu-system-arm -M realview-pb-a8 -nographic -kernel prog_arm_rpb_a8.bin

Installing an ARM cross compiler on Ubuntu

Here I will describe my installation of an ARM cross compiler, on an x86 machine with Ubuntu Linux.

Updates to this post

  • July 12, 2013 – changed to a later version of the Sourcery ARM compiler – now using version 2013.05-23
  • March 1, 2013 – changed to a later version of the Sourcery ARM compiler – now using version 2012.09-63

I had decided to use the Sourcery ARM compiler, formerly from CodeSourcery and now from Mentor.

I go to the page

http://www.mentor.com/embedded-software/sourcery-tools/sourcery-codebench/editions/lite-edition/

at which I decide to use the EABI release for ARM processors.

Then, I continue to the installation page for the ARM EABI version.

After having created an account (this was my first time here) and then logging in, I get an e-mail with a download link from which I can proceed to a page where I can download the IA32 GNU/Linux Installer. Doing this results in download of a file named arm-2013.05-23-arm-none-eabi.bin.

I make the file executable by doing

chmod +x arm-2013.05-23-arm-none-eabi.bin

and then I run the file, using the command

./arm-2013.05-23-arm-none-eabi.bin

This command results in an error message, and I am instructed to issue the command

sudo dpkg-reconfigure -plow dash

and then answer the question that comes up as instructed by the error message.

Now, again running the command

./arm-2013.05-23-arm-none-eabi.bin

results in the installation being started. After having gone through steps involving reading and accepting license agreements, followed by a decision to not create any symbolic links, and to not send anonymous information about usage of the ARM compiler, the installation is complete.

As a last step, I modify the PATH environment variable using the commands (where /home/ola is my home directory)

export ARM_GCC_LOCATION=/home/ola/CodeSourcery/Sourcery_CodeBench_Lite_for_ARM_EABI/bin
export PATH=$ARM_GCC_LOCATION:$PATH

I put the above two lines in a setup file, called setup.sh, that I run every time I want to use the ARM toolchain.

Now I can start programming for ARM!

As an example, I can compile, link, and run the example described in Chapter The Bare Metal in the book Into Embedded.

Connecting the views also at code figures

The Books with Views book creation software now generates links between the views also directly after figures showing code. As an example, you can try the links directly after Figure 3 in Into Programming.

In addition, the web-version of each book now contains links at the end of each section, linking to the next section in the book.

Intoembedded – a first draft version

A first draft of a new Book with Views – Into Embedded – is released. It has two views, one for the 32-bit Intel-x86 architecture and one for the ARM architecture. You can find more info at the Books with Views blog.