iPod Linux

7/28/2019 iPod Linux

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Development of Linux Based PDA-Like Applications

on Modern mp3 Players

Abstract- This paper presents a critical investigation intofeatures of some ultra modern music players that are similar to

those of a Personal Digital Assistant (PDA). In particular, the

work presented in this paper is centered upon a family of digital

music players called iPods developed by Apple Computers. Due

to the availability of almost perfect hardware & software systems

on these devices, modern music players like iPods are very

efficient computing devices. The paper also highlights various

subtleties in architectures & features of iPod and the traditional

devices like Sonys Walkman. The work presented in this paper

involved a customized version of Linux, which was run on iPod.

With the Linux as operating system and the complete hardware

system of iPod, the player provides an excellent opportunity to

develop applications on it & enhance its PDA-like features. A

thorough investigation of embedded systems in general and of

iPods in particular has been carried out in this work. Theprocedure to develop applications on iPod is discussed in this

paper, starting from running Linux on iPods hardware. Many

complex and new applications then can be programmed on iPod

keeping in mind some basic rules and facts about the hardware

and firmware involved.

I. INTRODUCTION

Music has always been a favorite and easily available

source of enjoyment for people across the globe for several

generations now. The technological advancements have led to

the development of several types of music players. Like other

electronic gadgets, music players have also greatly benefitedfrom transistors; the building block of all electronic systems.

The use of transistors resulted in miniaturization of the player,

giving listeners wide range of choices to enjoy music

anywhere anytime from the handheld devices. This started

setting up a new stage for business in a relatively new sphere.

The first Sony Walkman stereo (model TPS-L2) was sold in

1979 [1]. The trademark Walkman became so popular that it

evolved into a generic term, and lost its own identity. Sonycontinues to use the "Walkman" brand name for all kinds of

portable audio devices.

The recent surge in the VLSI and Embedded Systems has

created tremendous growth in media player industry. The

advent of flash memory and hard drives memoryrevolutionized the world of music lovers by reducing the size

of the device to that of a matchbox, and providing memory

space as large as 120 GB [2]. Listeners can now store

thousands of songs, hundreds of movies, photographs etc and

listen/watch or see the stored contents anywhere, anytime.These devices mainly deal with digital audio data. With no

mechanical part inside these players, there is no need to worry

about the wear and tear issues which were earlier involvedwith traditional music players like Walkman.

While modern research in the field of Error Correcting

Codes has resulted in a greater protection against scratches or

any other source of data corruption on CD, a similar

advancement in Information Theory has helped manufacturers

pack huge amount of data in a comparitively smaller space.

This means the players can now hold more music than everbefore and can deliver excellent quality sound at a relatively

higher intensity.

Being digital in nature, modern music players deliver high

fidelity sound over a wider frequency spectrum and at a very

high intensity level. Apple Computer iPod, shown in Fig. 1,

for example, can deliver high fidelity sound quality atintensity level as high as 120 dB [3]. Recently its ability to

deliver high intensity music has triggered a debate in thescientific community, regarding its role in causing Noise

Induced Hearing Loss (NIHL) [4-6].

The iPod, being one of the latest music players in the

market, is a result of tremendous research efforts made by the

professionals engaged in Research & Development activities

of the company. Due to enough hardware and software

resources, modern music players like iPod bear excellent

PDA-like features, in addition to the superior music quality.The existing hardware and software resources on the iPod may

also provide an opportunity to develop more PDA-likeapplications. Thus the same device, which is used as a music

player, can thus, be used as a multipurpose gadget. However it

becomes a tough job for third party embedded systems

professionals to seriously indulge in computing on these

devices. The reason is that the internal details of the player are

often obscured from the general public and may be available

only to the professionals of the company itself. It may,

however, be possible to access a lot of the resources of theplayer by rigorous reverse engineering. For example, some

serious reverse engineering and discussion within the

electronics industry unearthed unusual details of Apple's iPod

development process [7-9]. As a result of this it is now

possible to run a customized version of Linux kernel onto the

iPod hardware [10]. With full access to the operating system

and the hardware resources, the stage gets set for the nextlevel of challenge i.e. enhancing already included features anddeveloping newer ones.

Traditional research on modern music players most of the

time focuses on the quality of the audio itself. The work

presented in this paper is however concerned with the PDA-

like features of iPod

The organization of this paper is as follows: Section II

presents an overview of architecture of some modern music


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players such as iPod. The section also highlights some of thefeatures of the iPod that ranks this player on top. Section III

explores the other face of the coin; the PDA-like features ofthe player and highlights the fact that modern audio players

are very good embedded computing platforms. Section IV

describes in detail, the steps one would take to run Linux on

the iPod & start programming on the player. Section V

presents some of the conclusions drawn so far from the

research. Although not much literature is available on thesubject, the authors have provided a list of references, which

can immensely help anyone thinking of seriously indulging iniPod based computing.

II. ARCHITECTURE OF SOME MODERN MUSIC PLAYERS

The introduction of Apple Computer's iPod coupled with

iTunes software in 2001 was a big success. Since then Apple

has almost captured the whole market. Although Apple is

facing fierce competition with other companies, latest beingMicro-Star International's MSI MEGA 540 [11], the first solar

powered player, still there is no synonymous of iPod's

popularity. iPod has become so popular that the term "iPod"translated into a generic term. People now prefer calling any

portable audio player "iPod" instead of the company's

assigned name of the device. Basically the player consists of

the following unit:

LCD Driver/Controller

Video Decoder and Processor

Figure 1 iPod Nano

Figure 2. General architecture of modern music players

Power Management and Battery Charger

Battery

Audio Processor

Memory

Hard Drive Unit

Audio Codec

Fig. 2 shows a general block diagram of a portable audioplayer.

As a result of rigorous reverse engineering and disscussions

among embedded computing professionals, iPods internaldetails have been revealed [12]. The iPod uses two ARM7

TDMI-derived CPUs running at 90 MHz, 1.8 inch or 46 mm

ATA hard drives (with a proprietary connector) made by

Toshiba, a dedicated MP3 decoder and controller chip from

PortalPlayer, a stereo digital-to-analog converter from

Wolfson Microelectronics Ltd, a flash memory chip from

Sharp Electronics Corp., and a power management and batterycharging IC from Linear Technologies Inc. Generally the iPod

also has 32 MB of RAM (except the 60 GB 5 th generation iPod

which has 64 MB). A portion of the RAM is used to hold the

iPod OS loaded from firmware, but the vast majority of it

serves to cache songs loaded from the storage medium. For

example, an iPod could spin its hard disk up once and copyabout 30 MB of upcoming songs into RAM, thus saving

power by not having the drive spin up for each song

separately.

The current iPod models use internal Lithium-ion batteries

while 1st and 2nd generations of iPod used Lithium polymer

batteries. The larger models use audio circuitry provided by

Wolfson Micro-electronics and use touch wheels provided by

Synaptics. The iPod shuffle uses the SigmaTel STMP3550


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chip which handles both the music decoding and the audiocircuitry.

When power is first applied to the iPod the hardware startsexecution of code located at the ARM boot location that is

0x0. This location normally maps to the flash [17]. The first

flash sector contains the ARM reset vectors with the reset

vector pointing to the location where the bootloader is stored.

The bootloader then executes and in the simplest caseloads

operating system from the HDD and then executes that.

In its race to beat all the players in the market, the computermaker has faced some lawsuits as well. In 2005, for example,

the company faced two lawsuits claiming patent infringement

by the iPod and its associated technologies:[13], Advanced

Audio Devices claimed the iPod breached its patent on a

"music jukebox",[14] while a Hong Kong-based IP portfolio

company called Pat-rights filed a suit claiming that Apple's

FairPlay technology breached a patent [15] issued to inventor

Ho Keung Tse. The later case also includes the online musicstores of Sony, RealNetworks, Napster, and Musicmatch as

defendants [16].

III. AN INSIGHT INTO PDA-LIKE FEATURES OF iPOD

Audio player manufacturers are putting their best mind and

money to get a bigger share of the market. Sometimes it is justa marketing gimmick to attract consumers, and at other times

it is a real innovation. The incorporation of PDA-like features

into iPod is an example of an innovation, which helped the

computer maker get rid of the crises from which it was

suffering before the introduction of iPod. People can now

listen to the music while watching the photographs as slide

show. The iPod bundles a lot of PDA like features such as

Photo viewer, games, calendar, address book, notepad etc. Theplayer like iPod also has adequate embedded computing

environment to set the stage for newer application

development so as to compete with a dedicated PDA. With

some rigorous reverse engineering, embedded professionals

have successfully ported a customized version of Linux kernel

and played video on iPod Nano, which was not possible earlier

with the proprietary OS provided by Apple. The exact method

to install Linux is described in detail in section IV.

The biggest hurdle one faces in developing applications on

iPod is the black box appearance of the player. The companyhas always been tight lipped when it comes to releasing

secretes of iPod. So it is a challenging task for the application

designers to interact with the hardware of iPod. It is expected

that in near future manufacturers will be more open towards

releasing chip details following the line of open source

software supporters. This will definitely generate a new waveof interest among the embedded computing professionals for

programming any device consisting of a CPU, memory and acouple of input output interfacing etc.

The iPod, for example boosted the diminishing market shareof Apple Computer and is now becoming famous for its PDA-

like features, apart from the excellent sound quality. With the

Linux kernel loaded onto the players hard disk one can

develop innovative applications suiting the need of the time &

money. Following are some of the examples of these

applications, which have been developed with Linux loadedonto the player [10]:

1. Make an iPod work with Linux machines and runLinux applications.

2. Remove volume caps (iPod sold in Europe, cap the

volume at 100 decibels; uncapped iPods can reach

more than 115 decibels.)

3. Turn the iPod into a universal remote.

4. Attach an external hard drive to the iPod to increase

its storage capacity.

5. Change the iPod's font and graphics.6. Watch movies on iPod in full-screen mode.

7. Plug iPod into any computer (even without iTunes)

and listen to music from the hard drive.8. Transfer photos to iPod without using iTunes.

9. Replace iTunes all together as the iPod's main

jukebox.

IV. PROGRAMMING THE iPOD

This section focuses on the programming issues on the

iPod. The programming has been done in C language on

SUSE LINUX operating system. This section describes step

by step procedure for developing a program to display the text

Aligarh Muslim University on the iPod screen. The authors

assume that the intended audiences are familier with the

general comand-line operations on Linux terminal.

Nevertheless, one may type man or info on Linux termnal,followed by the command to know exact details of the

command.

A. Step 1. Downloading necessary files

Following files will be needed to install Linux kernel on the

iPod:

1. Official Boot loader (for the 1st, 2nd, and 3rd

generation iPod) which can be downloaded from:

http://sourceforge.net/project/showfiles.php?

group_id=73079&package_id=101451&release_id=226112

2. The latest kernel from the nightly build can be

downloaded from: http://www.ipodlinux.org/builds/

3. For userland installation download iPodLinux FS

which is available at http://168.234.106.10/linuxos-2005-08-28-+extras.tar.bz2


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4. The cross-compiler for uclinux from:

http://www.uclinux.org/pub/uClinux/arm-elf-tools/.This compiler is necessary because iPod uses an

ARM processor, the architecture of which is quite

different from the one provided by Intel. Since the

intention is to execute the program on iPod, the

binary file generated on the PC must be in

accordance with the instruction set of ARMprocessor.

5. If programming is to be done with Windows, Cygwin

will be needed which is available at

http://www.cygwin.com/.

Cygwin (see screen shot in Fig. 3) consists of a

library that implements the POSIX (Portable

Operating System Interface) system call API in terms

of Win32 system calls a GNU development toolchain

(such as GCC and GDB) to allow basic softwaredevelopment tasks, and a large number of application

programs equivalent to common programs on the

Unix system [18]. But it is strongly recommended touse Linux instead.

6. TTKfor graphical applications

(http://ipodlinux.org/TTK). TTK is a GUI library for

the iPod, which may be used for developing graphicalapplications.

7. Podzilla2 API

(http://www.getlinux.org/~oremanj/t/pz2-api.pdf).

Podzilla 2 is a modular user interface for the iPod

based on TTK.

B. Step 2. Determining iPod Connection The example to demonstrate programming of iPod has been

done on Linux (SUSE 9.3) platform. Before programming first

of all it is determined what Linux device the iPod is connected

as. Simply connecting the iPod to the USB and typing the cat

Figure. 3 Screen-shot of Cygwin

command at the terminal can do this:

# cat /proc/scsi/scsiAttached devices:

Host: scsi0 Channel: 00 Id: 00 Lun: 00

Vendor: Apple Model: iPod Rev: 1.50

Type: Direct-Access ANSI SCSI revision: 02

Here scsi0 denotes that the iPod is connected to /dev/sda

For more details on cat command one may refer to Linux man

pages.

C. Step 3. Mounting the iPod

To explore the content of iPod it is first mounted. For this, a

new directory is created using mkdir command and, then it

is mounted using the command mount:# mkdir /mnt/iPodSongs

# mount -t vfat /dev/sda2 /mnt/iPodSongs

Once the player is mounted its contents can be browsed as a

normal file system.

To unmount the iPod the command umount can be used:# umount /dev/sda2

More help regarding these commands can be found in manpages or typing info followed by the command name on Linux

terminal.

D. Step 4. Backing up important files

Basically we have to port a customized version of uClinux.uClinux (pronounced as mu c Linux) is a version of Linux

designed for devices that lack a memory management unit

(MMU) [19]. The iPod has some MMU-type capabilities, they

are, however, not sufficient to support the Linux kernel.

Because it is quite possible to accidentally remove thevaluable data already present in the iPod, it is recommended

that before installing Linux, one must backup all the files

including the iPod boot loader and OS. Typing the following

commands on the Linux-terminal can do this:

# dd if=/dev/sda of=ipod_boot_sector_backup count=1

# dd if=/dev/sda1 of=ipod_os_partition_backup

E. Step 5. Creating a new partition

This partition will hold the root file system for Linux. Usingthe following command, one can create a partition:

# fdisk /dev/sda

F. Step 6. Creating a file system

Using the following commands creates the file system:

# mke2fs -j /dev/sda3

It is recommended to set the maximal mount count betweentwo filesystem checks to zero to prevent fsck being run on it:


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# tune2fs -c 0 /dev/sda3

G. Step 7. Installing LINUX The downloaded Linux kernel and the bootloader areextracted into a directory. Next, extract the Apple image from

the boot loader and create a new image including Linux and

Apple OS (the kernel is named uclinux-2.4.24-ipod2.bin):

#./make_fw -3 -o apple_os.bin -e 0 ipod_os_partition_backup#./make_fw -3 -o my_sw.bin -i apple_os.bin -l uclinux-2.4.24-

ipod2.bin loader.bin

NOTE: -3 is required in make_fw only for 4th generation

iPods.

Once this is done, the new image and kernel modules can be

copied to the iPod:

# dd if=my_sw.bin of=/dev/sda1

# mkdir /mnt/ipod# mount -t ext3 /dev/sda3 /mnt/ipod

# cp -r lib /mnt/ipod

# umount /mnt/ipod

If every thing goes fine till this step, it means that the Linux

is now successfully loaded on iPod. To boot into Linux simply

detach iPod from USB and reboot by holding down the menu

and the play buttons for 3 seconds to reboot it. Afterrebooting, keep the back button pressed to boot Linux,

otherwise the default interface will be loaded.

H. Step 8. Programming the iPod

For programming, a cross compiler is needed as describedabove in Step 1. The compiler for uclinux is available from

http://www.uclinux.org/pub/uClinux/arm-elf-tools/. Once the

compiler is installed, one can compile simple programs. Thefollowing program, for example, displays the text Aligarh

Muslim University

#include

int main(void){ puts("Aligarh Muslim University "); return(0);}

The program is saved as display.c. The next step is to compile

the program:

# arm-elf-gcc -o display display.c -elf2flt

Once the binary is generated it is copied to the iPod:

# mount-t vfat /dev/sda2 /mnt/iPodSongs# mkdir /mnt/iPodSongs/myprogs

# cp display /mnt/iPodSongs/myprogs

After unmounting the partition one has to reboot the iPod in

podzilla, and scroll down to "File browser->/mnt/myprogs".

The option display" will appear at this stage. Clicking the

display option, one can see the program output on iPod screen.

For more complex GUI based programming it is

recommended to use TTK GUI library [20]. TTK is a library

for creation of graphical user interfaces on the iPod, alongwith a few other things

Figure. 4 iPod displaying the text Aligarh Muslim University

The other option is Nano-X/SDL, but TTK has some

advantages over these options. For example TTK is a higher-

level library and has intelligent event handling etc.

V. CONCLUSIONS& SCOPE FORFUTURE WORK

The aim of this paper is to highlight the ongoing research by

the authors involving some ultra modern mp3 players. As

presented in this paper, the popularity of modern musicplayers is not just the result of a superior sound quality, but

also because of the applications they can support. These

applications resemble to a large extent to those available on a

PDA. Moreover with the mutual growth in semiconductor

industry and embedded computing, it can now be anticipated

that the general trend of developing the newer applications

would continue to grow in future as well. These facts, coupled

with the hope that in near future the mnufacturers will be more

transparent as far as the internal chip detail is concerned,would mean easier access to the resources on the player. This

in turn would provide a platform for developing novel PDA-

like applications on the players; which would be a

breakthrough in the consumer electronics industry involovingmusic players. The users will just have to download the

application from internet in order to install it on the player.

Thus theplayer which is traditionally used for listening to the

music would turn out to be a multi-purpose gadget. The basicidea is to make use of the available resources of the player as

much as possible.

In particular, due to its unique features and some critical

issues and criticism associated with the Apple Computers

iPod, the authors have chosen iPod for this research. The


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authors have presented an example to illustrate a way todevelop a simple Linux-based application on the iPod. Various

complex PDA-like applications can then be developedfollowing the same line.

Furthermore, Linux, being an effort of Open-Source

Software Supporters, does not involve any kind of copyright

violation or patent infringement. This will provide a greater

freedom & flexibility to small-scale embedded computing

industry, especially in a developing country like India, toexperiment on the player and enhance its PDA-like features.

REFERENCES

[1] The story behind the Sony Walkman,

http://lowendmac.com/orchard/06/0915.html

[2] Seagate to Launch 120GB iPod drives,http://www.macnn.com/articles/06/08/14/120gb.18.hdds.in.2006/

[3] Squeezing Apple Juice, A time line of iPOds lawsuits,

http://dfire.org/x2231.xml

[4] Play it by the ear,

http://www.hindu.com/thehindu/mp/2006/12/06/stori

es/2006120600400100.htm[5] M. Salim Beg, Heshsham F.Abdul Basit, Narayan Gehlot, Role of

Modern Music Players in Noise Induced Hearing Loss, All India

Seminar on Biomedical Engg. & Bio-Informatics, AEC, Agra, 24-25

March 2007.[6] Noies-Induced Hearing Loss,

http://www.hearinglossweb.com/Medical/Causes/nihl/nihl.htm

[7] Reverse Engineering of the iPod Stuns Apple, http://www.out-

law.com/page-4762

[8] Inside the Apple iPOD design triumph,http://www.designchain.com/coverstory.asp?issue=summer02

[9] Apple trying to keep iPod Nano chip manufacturers a

secret? http://www.tuaw.com/2006/09/18/apple-trying-to-

keep-ipod-nano-chip-manufacturers-a-secret/

[10] Linux on iPod, www.ipodlinux.org[11] MSIs Solar Mega Player 540,

http://www.engadget.com/2006/03/12/msis-solar-mega-

player-540/[12] Next-Generation iPod Details Unveiled

http://www.mobilemag.com/redirect.php?content=3802[13] Channel Register. Apple faces patent lawsuits over its

iPod,2005-03-10,

http://www.channelregister.co.uk/2005/03/10/apple_ipod_patent_lawsuit

s/

[14] U.S. Patent 6,587,403 Advanced Audio Devices'"music jukebox" patent. http://www.google.com/patents?

vid=USPAT6587403&id=oawMAAAAEBAJ&dq=6,587,43

[15] U.S. Patent 6,665,797 "Protection of software again

against unauthorized use" (corrected to "Computer

Apparatus/Software Access Control"),http://www.google.com/patents?

vid=USPAT6665797&id=QrR2AAAAEBAJ&dq=6,665,797

[16] AppleInsider. Apple, Sony among those named in new

DRM lawsuit, 2005-08-16,http://www.appleinsider.com/article.php?id=1235

[17] Firmware, http://ipodlinux.org/Firmware

[18] http://x.cygwin.com/

[19] Embedded Micro Controller Project, www.uclinux.org/

[20] TTK, An iPod GUI Library, www.get-

linux.org/~oremanj/t/ttk-api.pdf

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