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MP3 Player Box HOWTO
Konrad Rzeszutek conradus@iname.com
v1.1, 2001-04-19
This document describes how to build, configure, install, and use a
custom MP3 player box. It lists the necessary hardware and answers a
number of frequently asked questions.
______________________________________________________________________
Table of Contents
1. Introduction
1.1 Acknowledgments
1.2 Copyright
1.3 Feedback
2. MP3 box
2.1 Design
3. Necessary hardware
4. Server side software
4.1 NFS server installation.
4.1.1 Setting up the Configuration Files
4.1.1.1 /etc/exports
4.1.1.2 /etc/hosts.allow and /etc/hosts.deny
4.1.1.3 Starting the NFS server.
4.2 DHCPd server installation.
4.2.1 Installing DHCPd
4.2.2 Setting up the configuration files for DHCPd
4.3 PXE daemon
4.3.1 Installing PXE software.
4.3.2 Setting up the PXE daemon.
5. Client side software
5.1 Linux kernel
5.2 Linux filesystem
5.2.1 Creating initrd filesystem.
5.2.1.1 Creating initrd fs.
5.2.1.2 Mounting initrd fs.
5.2.1.3 Copying LRP filesystem to initrd fs.
5.2.1.4 Copying custom modules,
5.2.1.5 Preparing the initrd fs for NBP.
5.2.1.6 Conclusion
5.3 Configuring NBP (Network Boot Program).
5.4 Configuring startup scripts.
5.5 Configuring the infrared receiver program.
5.5.1 Getting scan-codes.
5.5.2 Compiling ARCaMP.
5.5.2.1 Different remote.
5.5.3 mpg123
6. Plexiglass box
7. Answers to Frequently Asked Questions
7.1 Can't compile the kernel. It says: "2nd: No such file or directory"
7.2 My remote doesn't work with ARCaMP
7.3 The Linux kernel can't mount the filesystem.
7.4 How do I bend plexiglass?
7.5 The system doesn't boot up after I take the video card out.
8. References
8.1 Remote control programs
______________________________________________________________________
1. Introduction
This is a build guide for a custom MP3 box, which has no harddrive,
floppy, or video card and boots from the network. It also fetches the
songs from the network. It is intended as template, quick reference,
and a template to building a custom MP3 box. Frequently asked
questions related to MP3 box building, its usage, problems, and
references are given.
1.1. Acknowledgments
Much of this information came from authors private ideas and source
files covered under GNU licenses. Huge thanks goes to Tom Jones (for
helping me design the box), Ryan Defelic (for his MP3 box being a
alpha-prototype), Steve Maroney (for asking me many questions), the
LRP project, and of course The Penguin (which sits on his shrine next
to my network closet :=) )
1.2. Copyright
Copyright (c) 2001 by Konrad Rzeszutek
Please freely copy and distribute (sell or give away) this document in
any format. It's requested that corrections and/or comments be
forwarded to the document maintainer. You may create a derivative work
and distribute it provided that you:
<20> Send your derivative work (in the most suitable format such as
sgml) to the LDP (Linux Documentation Project) or the like for
posting on the Internet. If not the LDP, then let the LDP know
where it is available.
<20> License the derivative work with this same license or use GPL.
Include a copyright notice and at least a pointer to the license
used.
<20> Give due credit to previous authors and major contributors.
If you're considering making a derived work other than a translation,
it's requested that you discuss your plans with the current
maintainer.
1.3. Feedback
I rely on you, the reader, to make this HOWTO useful. If you have any
questions, corrections, or comments, please send them to me,
conradus@iname.com, and I will try to incorporate them in the next
revision.
2. MP3 box
The sole and only reason why you, the reader, is engulfing yourself in
reading this material along with a nice warm container full with java,
is so that you:
<20> Wish to make a self-supportive box with only four cables sticking
out of it: an RJ-45 network cable, a power cable, and two RCA
cables (or just one 1/8 mini stereo plug).
<20> Have all your mp3's on a big-server, while this MP3-box would fetch
the files from the server.
<20> Have no floppy driver, no video card, nor any harddrive in the
MP3-box. Just a power supply, sound card, network card, memory,
cpu, and a serial infrared receiver.
<20> Be the envy of your friends :=)
<20> Play your mp3's using your remote without having to turn on your
workstation.
2.1. Design
Its important to keep certain things in mind:
<20> Size of the computer component (I was tempted to use PC104 boards,
but they were to expensive). Height of ISA/PCI cards (so that the
box doesn't look like a baby-AT case).
<20> The appealing side of the box - does it look like a square
rectangle, pyramid, triangle, or something even more weird?
<20> Paint. Do you want see-through box with flashing lights inside,
inconspicuous black box, or chrome looking?
<20> Cost. The absolute minimum (taking into consideration that you, the
reader, has no spare computer parts) is about $70 (excluding tax,
shipping, etc)
<20> KISS (Keep It Simple and Stupid) - take everything that's
unnecessary and get rid of it (parallel port, modem card, video
card, etc).
The idea behind this box is to separate tasks - the MP3-box can only
play the mp3's from a server, while you, the reader, can freely add
more files to your big-end server. Thus, the MPEG-box wouldn't need a
harddrive, nor floppy drive. It would boot the operating system from
the network (from the same server where the mp3 files are located).
3. Necessary hardware
The software running the decoding process (mpg123) can happily work on
a 486DX/66 or higher without any constraints. 16MB of RAM ought to do
fine as well. Any sound card that is supported under Linux should
work. The following list includes all the hardware I used:
<20> Pentium 120 downclocked to 90 Mhz (I needed to lower the
temperature of the CPU so that I wouldn't have to use a fan - just
a heatsink). Cost: $5.
<20> Unknown brand-name motherboard (AT-style, 4 PCI, 3 ISA, 4x DIMM,
Award BIOS) - if you are going to get rid of the video card (after
you have configured the machine) make sure you change the display
from CGA/EGA (or VGA) to None. Cost: $10.
<20> Small powersupply (50 or less watts would do). I got one from a
Compaq computer (the wiring on the powersupply didn't match the AT
P8/P9 connector standards, thus I had to match the cables and
rewire them to fit my AT motherboard). You could probably use any
powersupply as long as it gives you 12VDC and ground. You won't
need the 5VDC unless you have a keyboard, mouse, or floppy
connected. Cost: FREE (found the computer in a dumpster).
<20> Intel EtherExpress Pro 10/100 Management Network Card. Any network
card will do as long as it has PXE or BOOTP functionality - those
things are also known as network booting. Without this kind of
network functionality, you would need to attach a harddrive/zip-
drive/floppy-drive to boot the operating system from. Cost: $15
(Intel had a promotion and they were selling two for $30).
<20> Sound card. I got a Crystal CS424x card b/c its height was pretty
small compared to other sound cards. Cost: $15.
<20> Remote control. This is the difficult choice - if you pick a
Packard Bell remote, you will end up pulling your hair out. I got a
Logitech AST Remote. Before you get a remote, you ought to check
for software that will work with your remote. Cost: $5.
<20> Cabling - stereo RCA cables from RadioShack. Network cable and a
jack from local distributor of electronic components. Cost: $9.
<20> Small 8mm screws to screw the custom box together. Picked up at
Home Depot along with plexiglass. Cost: $2.
<20> Plexiglass - used to construct the custom box. Bending of the box
is pretty easy, as long you have a torch and don't burn your own
eyelashes with it. Picked it up at Home Depot. Cost: $10.
<20> Black paint so the box would look inconspicuous and color-match my
stereo rack. Cost: $2.
Total cost: $75.
4. Server side software
Before you proceed with installing the server-software, it would be
beneficial to review the following HOWTO's (in the listed order):
<20> Net-HOWTO <htttp://metalab.unc.edu/pub/Linux/docs/HOWTO/Net-HOWTO>
<20> Ethernet-HOWTO
<http://metalab.unc.edu/pub/Linux/docs/HOWTO/Ethernet-HOWTO>
<20> Diskless-HOWTO
<http://metalab.unc.edu/pub/Linux/docs/HOWTO/Diskless-HOWTO>
<20> NFS-HOWTO <http://metalab.unc.edu/pub/Linux/docs/HOWTO/NFS-HOWTO>
Particularly, the Diskless-HOWTO
<http://metalab.unc.edu/pub/Linux/docs/HOWTO/Diskless-HOWTO> contains
a wealth of information useful for this project.
The required software are mostly already installed on a stock Linux
distribution, but some might be missing. The ones that are usually not
found (dhcpd, pxe, etc) are included in the mpeg-box-project.tgz
<http://darnok.dhs.org/~konrad/projects/mpeg-box/data/mpeg-box-
project.tgz> file.
<20> NFS server. Also called nfs-server or just nfs
<20> TFTP server. Called tftpd.
<20> DHCPd server. There are two versions. The latest one supports
natively PXE extension (which my network card uses), but doesn't
support menu based booting - something I needed during the
development. I'm using v2.0 and for PXE extensions I'm using an
DHCP proxy (all these strange terms will be explained later on).
<20> DHCP Proxy server - PXE. Not needed if you are using the latest
version of DHCP. The package is called pxe. Make sure you pick the
latest one, or just use the one that's included in my file.
4.1. NFS server installation.
I presume you have read the NFS-HOWTO
<http://metalab.unc.edu/pub/Linux/docs/HOWTO/NFS-HOWTO> . If you
haven't, do yourself a favor and pick it up. Most of these information
are straight from that HOWTO.
Before you start setting NFS, make sure you have nfs-utils or nfs-
server package installed. If you don't have them, the dhcpd-2.0pl2
source code is included in the mpeg-box-project.tgz
<http://darnok.dhs.org/~konrad/projects/mpeg-box/data/mpeg-box-
project.tgz> file.
<20> Extract the file -
tar -zxvf mpeg-box-project.tgz
<20> go into 1st Step - configuring server/01 - dhcpd.
cd "1st Step - configuring server/01 - dhcp"
<20> From there run:
./configure
make
make install
Setting up the server will be done in two steps: Setting up the
configuration files for NFS, and then starting the NFS services.
4.1.1. Setting up the Configuration Files
There are three main configuration files you will need to edit to set
up an NFS server: /etc/exports, /etc/hosts.allow, and /etc/hosts.deny.
Strictly speaking, you only need to edit /etc/exports to get NFS to
work, but you would be left with an extremely insecure setup. You may
also need to edit your startup scripts.
4.1.1.1. /etc/exports
This file contains a list of entries; each entry indicates a volume
that is shared and how it is shared. Check the man pages (man exports)
for a complete description of all the setup options for the file,
although the description here will probably satisfy most people's
needs.
An entry in /etc/exports will typically look like this:
directory machine1(option11,option12) machine2(option21,option22)
where
directory
the directory that you want to share. It may be an entire volume
though it need not be. If you share a directory, then all
directories under it within the same file system will be shared
as well. For example it might be: /exports
machine1 and machine2
client machines that will have access to the directory. The
machines may be listed by their IP address or their DNS address
(e.g., machine.company.com or 192.168.0.8). Using IP addresses
is more reliable and more secure.
optionxx
the option listing for each machine will describe what kind of
access that machine will have. Important options are:
<20> ro: The directory is shared read only; the client machine will
not be able to write to it. This is the default.
<20> rw: The client machine will have read and write access to the
directory.
<20> and many more ...
For our MP3-box, we just need to read-only access to the directory
with mp3's. Suppose the MP3-box IP will be 10.0.0.8 and the directory
with our music files is /exports/media. The /etc/exports would look
like this:
/exports/media 10.0.0.8(ro)
4.1.1.2. /etc/hosts.allow and /etc/hosts.deny
These two files specify which computers on the network can use
services on your machine. Each line of the file is an entry listing a
service and a set of machines. When the server gets a request from a
machine, it does the following:
<20> It first checks hosts.allow to see if the machine matches a
description listed in there. If it does, then the machine is
allowed access.
<20> f the machine does not match an entry in hosts.allow, the server
then checks hosts.deny to see if the client matches a listing in
there. If it does then the machine is denied access.
<20> If the client matches no listings in either file, then it is
allowed access.
In general, it is a good idea with NFS (as with most internet
services) to explicitly deny access to hosts that you don't need to
allow access to.
The first step in doing this is to add the following entry to
/etc/hosts.deny:
portmap:ALL
Next, we need to add an entry to hosts.allow to give any hosts access
that we want to have access. (If we just leave the above lines in
hosts.deny then nobody will have access to NFS.) Entries in
hosts.allow follow the format:
service: host [or network/netmask] , host [or network/netmask]
Here, host is IP address of a potential client; it may be possible in
some versions to use the DNS name of the host, but it is strongly dep<65>
recated.
Suppose we have the setup above and we just want to allow access to
huh.com and arakis.dune.com, and suppose that the IP addresses of
these machines are 10.0.0.8 and.10.0.0.1, respectively. We could add
the following entry to /etc/hosts.allow:
portmap: 10.0.0.8, 10.0.0.1
For recent nfs-utils versions, we would also add the following (again,
these entries are harmless even if they are not supported):
lockd: 10.0.0.8, 10.0.0.1
rquotad: 10.0.0.8, 10.0.0.1
mountd: 10.0.0.8, 10.0.0.1
statd: 10.0.0.8, 10.0.0.1
4.1.1.3. Starting the NFS server.
The shell scripts which start the NFS server are usually in
/etc/init.d or /etc/rc.d. Depending on your Linux distribution, you
either need to run: netconfig, setup (RedHat) ; YaSt2(SuSe); turbo-
config (TurboLinux); or you are stuck editing /etc/init.d/nfs-server
files manually. If you run those programs, look for options that list
NFS or nfs-serveR and start those services.
4.2. DHCPd server installation.
DHCP (Dynamic Host Configuration Protocol) is a protocol for computers
to find out their IP address, gateway settings, netmask, and a lot
more. Its a quite nice off-load for the system administrator. The
reason why you want to use it is because when the MP3-box comes up, as
said before, it doesn't have a harddrive, nor floppy drive - therefore
it can't boot an operating system. But with a card that supports PXE,
the following happens:
<20> The network card starts sending a DHCP request to the network
<20> The DHCP server offers a IP for the MP3-box.
<20> The MP3-box gets the IP address and then procceds to send PXE
extension DHCP request - an extension to the DHCP, which is not
covered in the RFC.
<20> The PXE extension daemon issues the NBP (Network Boot Program) to
the card on the MP3-box.
<20> The NBP contacts the TFTP server and downloads the Linux kernel,
and the initrd.gz file. After that it runs the Linux kernel.
<20> The Linux kernel does what it has been programmed to.
Without the IP address, the system wouldn't be able to get the NBP,
neither the Linux kernel.
Setting up the DHCP daemon is a two stage process - installing the
binaries, and setting up the configuration file for DHCP.
4.2.1. Installing DHCPd
The version of DHCP I'm using comes from Internet Software Consortium
<http://www.isc.org/products/DHCP/>, the version is 2.0. You might
already have the binaries installed, if that's the case - skip this
section.
The source code is 1st Step - configuring server/01 -
dhcpd/dhcp-2.0pl2, go into that directory and issue the following
commands:
./configure
make
make install
The shell scripts which start the DHCP server are usually in
/etc/init.d or /etc/rc.d. Depending on your Linux distribution, you
either need to run: netconfig, setup (RedHat) ; YaSt2(SuSe); turbo-
config (TurboLinux); or you are stuck editing /etc/init.d/dhcpd files
manually.
4.2.2. Setting up the configuration files for DHCPd
The most important part of the /etc/dhcpd.conf file are the option
fields and the host field. For the v2.0 of ISC-dhcpd its necessary to
specify
option dhcp-class-identifier "PXEClient";
option vendor-encapsulated-options ff;
This will enable the DHCP server to recognize the network cards with
PXE as valid. Make sure you also have the host section filled out. For
example, for the MP3-box called swallow.eoh the host entry would look
like:
host swallow {
hardware ethernet 00:90:27:c1:dc:db;
fixed-address swallow.eoh;
}
This is allow the DHCP server to give the box with that MAC address
(which the network card displays during boot-up), the IP address
associated with the host swallow. How is the host associated with
10.0.0.8 - that's the job of DNS server (which you hopefully have
installed). If you don't have DNS, you can use flat-host resolution
and add into /etc/hosts the following line (replace the 00:90:27. ..
with your MAC address):
10.0.0.8 swallow.eoh swallow
Back to the program ...
Following is my /etc/dhcpd.conf file:
option domain-name "eoh";
option dhcp-class-identifier "PXEClient";
option vendor-encapsulated-options ff;
option subnet-mask 255.255.255.0;
default-lease-time 600;
max-lease-time 7200;
subnet 10.0.0.0 netmask 255.255.255.0 {
range 10.0.0.20 10.0.0.40;
}
host swallow {
hardware ethernet 00:90:27:c1:dc:db;
fixed-address swallow.eoh;
}
You can check your DHCP server by booting up a Windows workstation,
and change its IP address to Obtain an IP address automatically.
4.3. PXE daemon
PXE is standard for remote booting. The following information is taken
from 1st Step - configuring server/02 - pxe/pxe-README:
PXE is an extension to DHCP and also method of remotely booting. The
specs for PXE can be found at
ftp://download.intel.com/ial/wfm/pxespec.pdf
<ftp://download.intel.com/ial/wfm/pxespec.pdf>. The PXE daemon
provides two capabilities: proxyDHCP and PXE Bootserver. The PXE
daemon can be set up to provide either or obth of the capabilities.
Both capabilities are required.
proxyDHCP works in parallel with DHCP and provides the booting client
with a remote boot configuration options. ProxyDHCP provides the PXE
client(s) with the following information: remote boot prompt with
optional timeout, remote boot menu and PXE Bootserver discovery
options.
The PXE Bootserver is a capability provided by the PXE daemon. The PXE
Bootserver is the capability that provides the booting client with
boot images for a particular boot environment.
PXE Bootserver serves up requested NBPs (Network Boot Programs) to PXE
clients. PXE Clients locate PXE Bootservers using discovery
information provided to the client by proxyDHCP. The discovery method
used by the PXE client (multicast, broadcast or unicast) and the list
of available bootserver types is controlled by proxyDHCP. PXE
Bootservers always listen for all three types of discovery requests
and will respond to all valid requests.
4.3.1. Installing PXE software.
If you have RedHat or SuSE, pxe is available as an RPM - download it
and install it. Unfortunately, you are still going to need the sources
- you will have to recompile the NBP (Network Boot Program).
All the paths mentioned below refer to the contents of the mpeg-box-
project.tgz <http://darnok.dhs.org/~konrad/projects/mpeg-
box/data/mpeg-box-project.tgz> file, which has all the source files
and configuration files listed below.
The source file for PXE server are located in
1st Step - configuring server/02 - pxe/pxe/pxe-linux/server.
If you don't have PXE installed, just run: make and make install. The
files will be installed in /usr/local. After that you should copy the
1st Step - configuring server/02 - pxe/pxe/pxe.init file to /etc/rc.d
or /etc/init.d. After that go into your /etc/rc2.d and link
/etc/init.d/pxe.init file to S99pxe. The command is:
ln -s ../init.d/pxe.init S99pxe
If you have no clue what I'm talking about, just enter
pxe
that will start the PXE daemon (but do that after you have read the
next section)
4.3.2. Setting up the PXE daemon.
To get the PXE daemon completely working, its necessary to setup a
couple of configuration files/directories.
<20> pxe.conf which is located in 1st Step - configuring server/03 - etc
files should be copied to /etc. The differences between this file
and the one that comes with PXE software is small - the order of
boot programs is changed. The original pxe.conf is located in 1st
Step - configuring server/02 - pxe/pxe/pxe-linux/server/services.
<20> mtftpd.conf which lists multicast addresses and the files
associated with it. Its better to leave the file alone. Copy it
from 1st Step - configuring server/03 - etc files into /etc
directory.
<20> The file /etc/inetd.conf needs to be modified so that it will
include support for TFTP (in case MTFTP doesn't work) and MTFTP.
The lines that should be added are:
mtftp dgram udp wait root /usr/sbin/tcpd in.mtftpd /tftpboot
tftp dgram udp wait nobody /usr/sbin/tcpd in.tftpd
<20> Add into /etc/services:
mtftp 1759/udp
pxe 67/udp
pxe 4011/udp
This will your life a little simpler when you are going to debug net<65>
work problems.
<20> The last thing will be to create the /tftpboot directory with all
the files in it. Do the following command:
mkdir -p /tftpboot/X86PC/UNDI/BStrap
mkdir -p /tftpboot/X86PC/UNDI/linux-install
The copy the bstrap.0 file (which is located in 1st Step - configuring
server/02 - pxe/pxe/pxe-linux/server/services into /tftp<74>
boot/X86PC/UNDI/BStrap. Do the same thing for linux.0, but copy it
into /tftpboot/X86PC/UNDI/linux-install. If you don't like any of
these patchs, modify the /etc/pxe.conf, /etc/mtftpd.conf accordingly.
After all these steps, make sure you have a DHCP daemon running and
working (look in the section about DHCP to find out how). Start the
pxe daemon by typing
pxe
Turn on your system with a network card that supports PXE. You should
see the card getting an IP from the DHCP server, and then showing up a
menu. If that's the case, you have successfully configured the server
system, and its time to get configure the Linux kernel and initrd file
for the MP3-box in the next section.
5. Client side software
The name of this section is rather misleading - since we are booting
the system remotly, all the software is not located on the client, but
rather on the server. The software, which includes the Linux kernel
and a small Linux distribution is under 2MB of space. It could
probably be squished into 1.44MB (so that it would fit onto a floppy)
but its more fun to remotly boot the MP3-box, and not use floppies.
The Linux kernel used was 2.2.16. Any versions can be used. The mini-
distribution used is LRP <http://www.linuxrouterproject.org> - it
normally fits on a 1.44 floppy compressed. The only thing that was
left from the original mini-distribution is the binaries - the rest
was changed by me.
5.1. Linux kernel
Making a new kernel for the MP3-box is a necessity. Your sound card
will inevitable different than mine, and you might have a different
network card.
The Linux kernel tree that I used is supplied. Look in:
2nd Step - configuring client/01 - linux kernel/linux-2.2.16
and type:
cd "2nd Step - configuring client/01 - linux kernel/linux-2.2.16"
make menuconfig
and choose the right drivers. If you want to use my startup scripts
for the mini-linux distribution, make all the drivers modularized
(network, filesystem, sound card).
After successfully choosing your drivers, make the kernel. Copy your
new kernel 2nd Step - configuring client/01 - linux
kernel/linux-2.2.16/arch/i386/boot/bzImage into your tftpboot
directory as linux.1 (not as linux.0!)
cd "2nd Step - configuring client/01 - linux kernel/linux-2.2.16"
make bzImage
cp arch/i386/boot/bzImage /tftpboot/X86PC/UNDI/linux-install
Presumably, you configured your network, sound drivers as modules. It
will be necessary to compile them and put them in temporary directory
(until you get the the mini-distribution setup). To compile and
install in temporary directory do:
export INSTALL_MOD_PATH=/tmp
make modules;make modules_install
The modules for the kernel will be located in /tmp/lib/modules/2.2.16.
Remember that path.
5.2. Linux filesystem
We need to make a filesystem that the Network Boot Program can
download from the server, and pass to the kernel. The maximum size of
such filesystem is limited to the amount of memory in the machine, but
generally it shouldn't be bigger than 4MB.
Since we want to boot the MP3-box from the network, and have no media
storage device on the MP3-box, the filesystem cannot be on a
harddrive, floppy drive, nor ZIP drive. Linux provides a facility for
that called Initial RAM Disk (initrd) - its a file, which actually is
a ext2 filesystem embedded in a file.
5.2.1. Creating initrd filesystem.
To understand why we need to create a INITial Ram Disk filesystem, its
necessary to understand how Linux boots up.
<20> After the kernel is finished loading itself, it starts executing
itself.
<20> The kernel converts initrd (which the boot loader loads into memory
as linux.2) into a "normal" RAM disk.
<20> When its done, it mounts the device specified in root_dev (which is
changed by the Network Boot Program). This usually points to
/dev/ram0 or /dev/ram1.
<20> /linuxrc is executed.
<20> When linuxrc terminates, the "real" root file system is mounted
(which can be the RAM disk)
<20> /sbin/init is invoked.
For more info, man initrd.
5.2.1.1. Creating initrd fs.
The initrd - is a initial ram disk embedded inside a file. Creation of
such a file is quite straightforward (you have to be root to use
losetup).
dd if=/dev/zero of=/root/initrd count=4096 bs=1024
losetup /dev/loop0 /root/initrd
mke2fs /dev/loop0
losetup -d /dev/loop0
file /root/initrd
This creates a initrd file 4MB big. The last command should say:
Linux/i386 ext2 filesystem. This is the file that we eventually use to
boot the Linux OS on the MP3-box.
5.2.1.2. Mounting initrd fs.
To use the initrd for something its necessary to make a mount-point a
mount the initrd file:
mkdir /data
mount /root/initrd /data -o loop
Now you freely copy files back and forth onto the 4MB initrd file,
which is mounted under /data.
5.2.1.3. Copying LRP filesystem to initrd fs.
Its time to put something meaningful on the 4MB initrd. We need to
copy a small linux distribution onto the initrd, otherwise we can't
use it boot the MP3-box.
cd "2nd Step - configuring client/02 - the filesystem"
tar -cf - * | (cd /data; tar -xvf - )
5.2.1.4. Copying custom modules,
Do you remember the modules that we compiled in the previous section?
cp -Rf /tmp/lib/modules/2.2.16/* ./data/lib/modules/2.2.16
sync
df -h
df -h serves only to show you how much space you have left on the
filesystem.
5.2.1.5. Preparing the initrd fs for NBP.
Using the initrd file generally means we have to unmount the file,
gzip it and copy it into the tftpboot directory.
umount /data
sync
gzip -c9 /root/initrd > /tftpboot/X86PC/UNDI/linux-install/linux.2
This will unmount the initrd, and compress it into linux.2 file (which
is what the NBP will look for and download).
5.2.1.6. Conclusion
That's basicly the method of designing and using an initrd filesystem.
One thing to keep in mind - the initrd should always be compressed
when deployed.
5.3. Configuring NBP (Network Boot Program).
After you have copied your initrd file and tried to boot up the
workstation, you found out that the kernel complains about not being
able to mount the root partition. The problem lies in the NBP that is
supplied with PXE - it was compiled for RedHat type initrd images, and
therefore does some changes to the kernel.
<20> When the NBP is finished downloading the kernel, it sets the
root_dev environment to whatever was compiled inside the NBP. By
default, that is 0101, which is /dev/ram1 (look at its major,
minor).
<20> NBP passes the environment to kernel (in and in turn overwriting
whatever settings the user supplied to the kernel using rdev) and
starts it.
<20> The kernel happily executes and tries to mount a filesystem from
/dev/ram1>, while the initrd image sits in /dev/ram0.
<20> The kernel hangs.
The solution is to recompile the NBP with the right root_flags.
Look in
1st Step - configuring server/02 - pxe/pxe/pxe-
linux/nbp.linux/prepare.c. Line 212 lists the hexadecimal address.
Change it to 0x0100 - that way the kernel will mount /dev/ram0 and
actually find a initrd filesystem.
5.4. Configuring startup scripts.
When the kernel completes loading the initrd into memory and mounts it
as a filesystem, then /sbin/init is executed, which handles the rest
of starting the operating system.
<20> init reads in /etc/inittab - which lists which scripts must be
executed depending on the computer's state.
<20> It starts executing the boot-time configuration script
/etc/rc.d/rc.boot.
<20> rc.boot setups BusyBox and POSIX links, configures all the modules
- sound, network, and filesystem. If you are using your own
modules, you must edit this file and change the settings.
<20> Then init changes the runlevel to its default - 2, which result in
running /etc/rc.d/rc.multi.
<20> rc.multi setups the network card (configures its IP), mounts the
NFS server and starts the audio-subsystem (/etc/rc.d/rc.audio). It
gets all the custom configuration (where is the NFS server. its IP,
etc) from /etc/rc.conf.
<20> rc.audio configures the sound, creates playlists, and starts the
ARCamp program (which listens to the remote and runs/kills mpg123).
The scripts were made as simple as possible. The files you ought to
look into and alter are:
<20> /etc/rc.conf - has the NFS IP, the mountpoint, and the client's IP
<20> /etc/rc.d/rc.boot - loads the network module, and the filesystem
module.
<20> /etc/rc.d/rc.audio - loads the sound card module.
5.5. Configuring the infrared receiver program.
The Logitech Remote I obtained was quite easy to get working with
Linux. The software used in Linux was ARCaMP (AST Remote control MP3
Player). The software basicly listens at the serial port for some
predefined characters, and based on them, launches mpg123.
5.5.1. Getting scan-codes.
The source code is included in 2nd Step - configuring client/99 - the
sources/ARCaMP. It differs from the original code - the key mappings
are different and the default playlist has been altered. If you find
out that the program works with your remote, but the buttons -> action
mappings are screwed up, then edit the defs.h to match your scan-codes
with your remote. Getting the scan-codes is quite easy:
cat /dev/ttyS1 | od -t x2
0000000 2000 7f10 7f10 7f10 7f10 7f10 7f10 7f10
0000020 7f10 7f10 202a 7f10 7f10 7f10 7f10 7f10
0000040 7f10 7f10 7f10 7f10 7f10 7f10 202a 7f10
0000060 7f10 7f10 7f10 7f10 7f10 7f10 7f10 202a
0000100 0f0f 0f0f 0f0f 0f0f 0f0f 2a0f 0f20 0f0f
0000120 0f0f 0f0f 0f0f 2a0f 0f20 0f0f 0f0f 0f0f
0000140 0f0f 0f0f 202a 1212 1212 1212 1212 2a12
0000160 1220 1212 1212 1212 1212 2a12 1220 1212
0000200 1212 1212 1212 1212 1212 202a 1212 1212
/dev/ttyS1 is the serial port for my infrared receiver, yours might be
different. od -t x2 converts the output to hexadecimal.
The first eight bytes are just offset locations - ignore them. If you
look closely at the strings it becomes clear that whenever you hit a
the same button on the remote, you get similar looking strings of
numbers. The first three rows are actually the fastforward button
being hit three times. The repetition of ox20, ox2A, 0x7F, and 0x10
suggest that 0x20 and/or 9x2A are remote-id number, while 0x7F or 0x10
are codes for fastforward.
The next three rows are for the play button (the scancode is 0x0F).
And as you can see, the repetition of 0x20, 0x2A suggest remote-id
again.
The last three rows are for the stop button - 0x12.
5.5.2. Compiling ARCaMP.
Just run make and copy the arcamp file into /data/bin directory -
assuming you still have the initrd filesystem mounted under /data.
5.5.2.1. Different remote.
If you have different remote, and the scancode-match procedure doesn't
work, then you won't be able to use ARCaMP. Instead you will have to
search for some software under Linux that will support your remote.
Look at the ``Remote control programs'' section at the end of the
document for some URLs.
Just keep in mind, that you will have to modify /etc/rc.d/rc.audio (on
the initrd fs) so that it will spawn a different program then ARCaMP.
5.5.3. mpg123
The program is staticly compiled and put in /bin (on the initrd)
directory. If you find it necessary to get a more recent version ,
recompile it with -static flag and put in /bin.
6. Plexiglass box
The box can be made of wood, metal or anything else. But the most
simplest way of building ones box is to use plexiglass. Plexiglass
under heat - from a torch, kitchen stove - will warm up and is
susceptible to bending. The disadvantage of plexiglass is that its can
carry electric charge - thus its unadvisable to put electronic
components on the plastic - use those small plastic pegs for
motherboards - glue them on the plexiglass.
The design of the box depends on your parts. If you have a small
motherboard, low-profile sound card and network card, you can make the
box 4"-5" tall. The placement of motherboard, power supply, and the
infrared serial receiver all depends on your imagination.
In the case of my box, the minimum I could get was 6" height (the
motherboard + plastic pegs + ISA Sound card). Therefore I decided on
building a wide box to compensate for the height. The shape of the box
is semi-pyramid.
During the design, heat and air circulation has to be taken into
account. If you wish to make your system noise-less (without fans),
make the box big, and drill holes on sides, and on the top so that hot
air can raise and escape. You also might consider downclocking the CPU
- that way you can use a heatsink instead of CPU fan. Another
alternative is to drill holes one side of the box, and put a fan on
other side, and have the CPU in the middle of the air-flow. Take also
in consideration your power supply. The small power supplies (83W,
40W) don't exhaust too much heat and can be safely left without a fan.
Unfortunately, the bigger they get the more heat they exhaust - and
the heat has to be drawn out.
In my case I decided to use one fan to cool down the power supply and
CPU. The fan is mounted on top of the power supply. The power supply
has exhaust vents on top, from which heat escapes. The CPU is located
20cm away from the fan, under 45" angle - also not that far away from
the CPU I drilled some holes to suck in fresh air. What essentially
happens is that outside air is sucked in thru the holes, passes over
the CPU and then combined with the air from the power supply is sucked
out by a fan. For pictures: check mpeg-box pictures
<http://darnok.dhs.org/~konrad/projects/mpeg-box/>.
7. Answers to Frequently Asked Questions
7.1. Can't compile the kernel. It says: "2nd: No such file or direc<65>
tory"
Move the whole linux-2.2.16 directory somewhere else where the
directory-name doesn't have spaces in itself.
7.2. My remote doesn't work with ARCaMP
Tough! :P
You will have to look for some other software that will support your
remote control. Look in the ``Remote programs URL'' section.
7.3. The Linux kernel can't mount the filesystem.
Look in ``Configuring - NBP Network Boot Program''
7.4. How do I bend plexiglass?
Get a torch and heat the opposite side of the plexiglass that you are
going to bend. You should move the torch back and forth, not to fast,
and not too slow. One minute - two minutes should be fine, if you warm
up it too much, bubbles will appear. After you have heated the
material, put in on table and slowly bend it. Keep it under the
desired angle up to a minute.
7.5. The system doesn't boot up after I take the video card out.
Go into the BIOS settings and change the Video Mode (it might be
called something else on your system) and change from CGA/EGA or VGA
to None.
8. References
8.1. Remote control programs
<20> IRC is a package that supports receiving and sending IR signals of
the most common IR remote controls. It contains a daemon that
decodes and sends IR signals, a mouse daemon that translates IR
signals to mouse movements, and a couple of user programs that
allow to control your computer with a remote control. www.lirc.org
<http://www.lirc.org>
<20> Cajun is a program that allows you to turn any computer (>75mhz)
into a massive audio jukebox for your car or home. It uses the
matrix-orbital serial display and supports the IRman infra-red
remote control interface. Soundcard output is delivered to your
(car or home) stereo for amplification. The software supports a
hotlist and shuffle mode. cajun.sourceforge.net
<http://cajun.sourceforge.net>
<20> IRMP3 is a multimedia audio jukebox for Linux. IRMP3's strength is
that it easily integrates into home, car, and mobile environments
(where a keyboard/screen interface may not always be available). It
supports several input and display devices such as infrared remote
controls, LCD displays, network connections, and serial keypads. It
includes a robust set of tools like alarms, sound environments,
mixers, sleep functions, and more. It supports MP3 players and
network-ready control & status monitoring, and includes a flexible,
modularized source which allows functionality to be easily extended
with user-developed code. www.dpotter.com/irmp3
<http://www.dpotter.com/irmp3>
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