Linuxstamp

Status

We now have the linuxstamp prototypes. Several of the features have been tested.
Working

• Power supply (after mod)
• USB->Serial converter
• SDRAM
• DATAFLASH
• JTAG
• SD card
• reset switch (after mod)
• USB Host

Untested

• Ethernet

Not working

Description

The Linuxstamp is designed to be a general purpose processor module. It is designed to work as a stand alone module (SD card, ethernet and USB/Serial converter are all on the module). This allows all initial development to be done without a motherboard, but for integration into a specific project a motherboard with specific features could be designed. Check out the start of the first mother board for the linuxstamp, Mboard 1.

Features

• Atmel AT91RM9200 processor (Arm9 processor with MMU)
• 32MB SDRAM (Only limited by 1x 54-TSOP SDRAM chip)
• 8MB SPI Dataflash
• 1x 10/100 Ethernet
• 1x USB host port (allows wifi adapters, flash drives and other USB devices to be used)
• 1x SD card slot
• Serial debug port access through FTDI USB/Serial converter
• JTAG port
• 2-Layer PCB design
• POE capable (48v -> 5v Power supply can be implemented on a motherboard)

Licence

All files for this project are licensed under the GNU GPL V2

Project files

Warning!!! This is an untested design. As testing results are available I will post them on this site.

• PCB Top view (pdf)
• PCB Bottom view (pdf)
• Schematic (pdf)
• Project zip file

Power

The power supply for the board is based on the Linear LTC3407-3. This is a very compact high frequency switching power supply. It has both a 3.3v and a 1.8v output. It does have a very tight input range 3.3v-5.5v. The Micrel PHY also needs 2.5v, but this is provided by an internal regulator. Currently a regulated 5v must be used to power the board. Talking with Jeff from Jendy Labs it seems like POE (Power Over Ethernet) is a good idea. Wekipedia has a good general description of POE. The basic idea is that POE provides 48v and up to 13 watts, more than enough power for the Linuxstamp. The problem for the module is that a 48v -> 5v power supply is not small or cheap. In order to take advantage of POE without increasing the board size I found a part from Transtek Magnetics that is made for POE and has the rectifier built into the jack. The 48v lines are then connected to the pin header. This will allow a motherboard to integrate a POE power supply.

Minicom & the debug port

The USB device port on the linuxstamp does not connect directly to the AT91RM9200 it connects to the FT232R chip. The FT232R is a USB/serial converter. The FT232R chip has drivers for both Windows and Linux, but the Linux drivers are included in later kernels. When you plug the Linuxstamp into your host (linux) machine a device should appear /dev/ttyUSB0 (I think the postfix number will incriment as you add more devices). /dev/ttyUSB0 will behave as any other serial port now. Minicom is the standard program to access the serial port in Linux. The first time you run minicom you will have to be root in order to do the setup, after that you can change the permissions on /dev/ttyUSB0 so any user can run minicom. To enter configuration mode in minicom type CTRL-A o, now scroll down to Serial port setup. Use the letters to navigate. You will want the device to be /dev/ttyUSB0 and Bps/Par/Bits to read 115200 8N1. Connection to the board is important for loading Atmel's tiny program and u-boot, but once the board is working it might not be as important.

nfs & tftp

Nfs (network file system) and tftp (trivial file transfer protocol) are two servers you will want running on your host machine. Nfs is useful for hosting the root file system of the Linuxstamp. Tftp is useful for u-boot to retrieve the kernel from. There are many other websites on nfs and tftp, but I will try and go over a simple setup. I would suggest being behind a firewall before trying either of these setups as neither is secure. I wrote this using a Fedora 7 system. First make sure you have nfs installed.

• $ yum install nfs-utils nfs-utils-lib portmap system-config-nfs

Now to make sure the service is enabled run:

• $ serviceconf and make sure nfs and nfs lock are ckecked

Now edit /etc/exports you should add a line like this /path_to_nfs_root/ *(rw,no_root_squash,insecure). Now restart nfs.

• $ /etc/init.d/nfs restart

You can test this with

• $ mount -t nfs server_name:/path_to_nfs_root /path_to_test_mount

Now on to tftp. Make sure it is installed.

• $ yum install tftp-server

This will create a file /etc/xinetd.d/tftp. In this file you will want to change disable from yes to no. Now make a test file.

• $ cd /tftpboot
• $ echo hello > file

Now we can test it

• $ tftp -v server_name -c get tmp

Cross Compilier

In order to compile for the AT91RM9200 we need to build a cross compilier. Dan Kegel has created a very useful tool for building a cross compiliers. I am using Fedora 6 (x86_64) as my host system. After downloading and extracting crosstool (I was using version 0.43) I made two small changes. In the "demo-arm.sh" file I changed the eval line to

• "eval `cat arm.dat gcc-3.4.5-glibc-2.3.6.dat` sh all.sh --notest"
  

In the "arm.dat" file I changed the TARGET to "arm-linux" (By default u-boot looks for arm-linux-* tools). Now if you run "demo-arm.sh" you should get a cross compilier.

Booting

The AT91RM9200 has several features the faciliate easy booting. There is a good description of the booting order here. Atmel provides a tiny program that lives in the Dataflash and loads u-boot (see next section).

U-boot

First we need the u-boot source found here (I was using version 1.1.6). If you have not yet built a cross compilier now would be a good time to do so (See the cross compilier section below). Now you can do a test for the Atmel AT91RM9200 DK board.

• $ make at91rm9200dk_config
• $ make

This should give you a "u-boot.bin" file. We will have to write a board specific configuration file for the Linuxstamp. We should be able to base it off the the Atmel DK board. If you look at "/u-boot-1.1.6/include/configs/at91rm9200dk.h" you can see the configuration for the DK board.

Busybox

Busybox provides the necessary utilties (e.g ls, cp, etc...). After you have downloaded and unpacked busybox we are ready to get started (I was using version 1.4.2).

• $ make defconfig

Now for a quick test we can make busybox for our host machine

• $ make

After you run this you should have a file 'busybox'. Now try

• $ ./busybox ls

But we want to build busybox for our embedded system so run

• $ make ARCH=arm CROSS_COMPILE=arm-linux-

If you want to make Busybox with all the symbolic links for the tools run

• $ make CONFIG_PREFIX=/path_to_dir ARCH=arm CROSS_COMPILE=arm-linux- install

Building the Kernel

If you have ever built the kernel for your desktop, then cross-compiling the kernel isn't that much harder. First get the latest kernel from kernel.org (I was using 2.6.23-rc9), then get the AT91RM9200 patch from here. After you unpack both of these you can apply the patch.

• $ patch -p1 < 2.6.23-rc3-at91.patch

Now lets take a look at the default configurations

• $ make ARCH=arm help

The ecbat91 is the closest to the linuxstamp.

• $ make ARCH=arm ecbat91_defconfig

If we what to further customize the build we can use 'xconfig'

• $ make ARCH=arm xconfig

Now we're are ready to build the kernel. You will have to have the u-boot tool mkimage in the PATH for this to work

• $ make ARCH=arm CROSS_COMPILE=arm-linux- uImage

Minimal filesystem

There isn't much you need for a minimal filesystem. I suggest creating a staging area to create the filesystem. First you need the libraries generated by the cross compilier on my machine they are located at /opt/crosstool/gcc-3.4.5-glibc-2.3.6/arm-linux/arm-linux/lib. Next you will need busybox, and we saw in the busybox section we can tell busybox where to output the files (use the root directory of your staging area). The last file we need is /dev/console. Make the directory.

• $ mkdir /staging_path/dev

/dev/console is a special file used to bind a device driver to a file. As such we use the mknod command.

• $ mknod /staging_path/dev/console c 5 1

The c says this is a character device. The 5 says this is major node 5, and the 1 says it is minor node 1.

Dropbear SSH

One of the first non busybox tools we will want is SSH. Dropbear is a small SSH client/server. I was able to build version 0.50.

• $ ./configure --host="arm-linux" --disable-zlib
• $ make

Eagle Stuff

I will put tools and libaries here.

• I would post a cam job, but opencircuits won't let me upload a .cam file

Links

• Atmel: AT91RM9200 info on Atmel's site
• [1]: Up to date kernel patch for the AT91RM9200
• Cadsoft.de: Free (as in beer) tools for schematic and PCB design
• openhardware.wordpress.com: Here is my openhardware blog
• App notes: for Atmel arm processors
• Jendy Labs
• Mborad 1 for the linuxstamp
• ECB AT91 This is another open source project similar to the Linuxstamp. They have somve very good documentation.

Pricing

The parts cost for qty 1 is $75 from digikey, and $55 for qty 100
I'm sure this can be greatly reduced with higher quantity
We will make a small run soon, and I will let you know when these are available.

Discussion

Can I plug a USB peripheral into the Linuxstamp, such as a USB Wifi adapter? --DavidCary 22:02, 17 April 2007 (PDT)

Yes, any USB device that is supported by the kernel should work with the Linuxstamp. --Linuxvolts 23:15, 18 April 2007 (PDT)

This is not a true USB port is it? Its just a usb serial peripheral port, therefore USB stick will not work.

Should be answered by the last answer, too. An USB stick is also USB peripheral^^ --SebDE

This is not a USB host....it (Linuxstamp)is seen as the peripheral surely?

From the Features:

1x USB host port (allows wifi adapters, flash drives and other USB devices to be used)

You can plug in any USB device that is supported by the kernel. The Linuxstamp is not supposed to be plugged via USB to a PC.

--SebDE

The AT91RM9200 has 2x USB host ports and 1x device port. I bring out one of the USB host ports directly from the chip to a USB A connector. There is also a mini USB B connector on the board this is connected to the FT232RQ (USB/serial converter) which in turn is connected to the debug serial port on the AT91RM9200. So the linuxstamp can be both a USB host and a USB device. --Linuxvolts 20:10, 4 July 2007 (PDT)

Contact

For further questions or comments please contact Paul (pthomas8589 _at_ gmail _dot_ com)