Bluetooth GPS on the mini2440 with GPSd

For a long time i’ve had a SiRF 3 bluetooth GPS which i’ve just connected to the mini2440 using a ludicrously cheap USB bluetooth adapter from DealExtreme. Including shipping it cost £1.38 delivered!! Here’s what you get for your money:

The chip is a Conwise CW6626. Anyway, what matters most is that if you have bluetooth configured it works out of the box!

Connecting to the GPS is easy. First check the interface:

hciconfig -a

If it says down bring it up:

hciconfig hci0 up

After executing the above I got the following:

root@mini2440:~# hciconfig -a
hci0:    Type: USB
BD Address: 00:15:83:15:A3:10 ACL MTU: 672:3 SCO MTU: 128:2
RX bytes:348 acl:0 sco:0 events:11 errors:0
TX bytes:38 acl:0 sco:0 commands:11 errors:0
Features: 0xff 0x3e 0x85 0x30 0x18 0x18 0x00 0x00
Packet type: DM1 DM3 DM5 DH1 DH3 DH5 HV1 HV2 HV3
Link policy:
Name: ''
Class: 0x000208
Service Classes: Unspecified
Device Class: Phone, Cordless
HCI Ver: 2.0 (0x3) HCI Rev: 0xc5c LMP Ver: 2.0 (0x3) LMP Subver: 0xc5c
Manufacturer: Cambridge Silicon Radio (10)

Now turn your GPS on and do a scan:

root@mini2440:~# hcitool scan
Scanning ...
00:0D:B5:32:2C:02    BT-GPS-322C02

Now fill in /etc/bluetooth/rfcomm.conf with the details. Here’s mine:

# RFCOMM configuration file.
rfcomm0 {
# Automatically bind the device at startup
bind yes;

# Bluetooth address of the device
device 00:0D:B5:32:2C:02;

# RFCOMM channel for the connection
channel    1;

# Description of the connection
comment "BT-GPS-322C02";

Next bind the device:

rfcomm bind rfcomm0

And check the device output using:

cat /dev/rfcomm0

Next i bitbaked gpsd, by simply typing:

bitbake gpsd

In my OE installation (see the various posts about setting this up).

Once this builds you can install the appropriate ipks. From memory I think i installed the following:






This pulled in a whole load of other packages. Next you can start gpsd by typing:

gpsd /dev/rfcomm0

And monitor the output using:


If all has gone well you should get a text output of the parsed NMEA data:

Anyway..that’s just the tip of the iceburg. If you want to learn more have a look at the gpsd website and the bluetooth page i have based this post on.

Qt Embedded 4.6.0 + Qwt + kxps5 accelerometer!

After testing the operation of the kxps5 accelerometer with i2c-tools i wrote a test application using the i2c-dev interface. If you want to test your code before you write a kernel driver this is definately a good place to start. Once i had the configuration registers set properly and i had a routine for reading the acceleration vectors I stripped down a ds1621 kernel driver to a bare minimum, and then built it back up again to work with the kxps5. I then bitbaked the kxps5 driver as a kernel module, along with hwmon and it works perfectly! 🙂 Next i cross compiled qwt 5.2.0 and plotted the acceleration as function of time. The video below is taken with antialiased lines which slows down the refresh rate but makes them look nice. If you plot it without this enabled it runs very smoothly. Here you see the kxps5 running without an external low pass filter (the internal filter is 1kHz) and despite this the output is pretty stable. What impressed me the most is the sensitivity. When placed on a desk the free fall interrupt indicator lights up if you drop one of the little nuts from the friendlyarm LCD about 10cm away from the device!


The kernel driver for this is now available here.

Bitbaking the kernel, Angstrom and qt4-embedded all at once

This is what i should have done to begin with! The instructions are very similar to previous ones except this time we clone the right git repository!

On a fresh copy of Fedora 11 I updated the system and installed the packages reccommended by OE:

su -cyum install python m4 make wget curl ftp cvs subversion tar bzip2 gzip unzip
python-psyco perl texinfo texi2html diffstat openjade docbook-style-dsssl
docbook-style-xsl docbook-dtds docbook-utils sed bison bc glibc-devel glibc-static
gcc binutils pcre pcre-devel git quilt groff linuxdoc-tools patch linuxdoc-tools
gcc-c++ help2man perl-ExtUtils-MakeMaker”

I then made a folder called OE in my home directory and git cloned the mini2440 repo:

cd ~

mkdir OE

cd OE

git clone git:// openembedded

I then setup the source-me.txt similar to before:

gedit source-me.txt

I put the following in:

export OETREE="/home/doug/OE"


echo Setting up dev env for Ångström

if [ -z ${ORG_PATH} ] ; then
export ORG_PATH

if [ -z ${ORG_LD_LIBRARY_PATH} ] ; then


export LANG=C

su -c 'sysctl vm.mmap_min_addr=0'

echo "Altered environment for OE Development"

Now all you need to do is setup the local.conf. Simply edit the example and copy it to the right place:

cd openembedded
gedit mini2440_local_conf_example.conf

Read this file and edit as appropriate. I have attached mine as an example. Now copy it to the conf/local.conf

cp mini2440_local_conf_example.conf conf/local.conf

If you want qt4-embedded or any other package included in the build simply edit the recipe in:


I added qt4-embedded:

#Angstrom bootstrap image

IMAGE_PREPROCESS_COMMAND = "create_etc_timestamp"


DEPENDS =  "task-base-extended
esekeyd u-boot-utils tslib
i2c-tools i2c screen rsync nfs-utils
directfb gdbserver directfb mtd-utils

IMAGE_INSTALL = "task-base-extended
psplash-zap qt4-embedded
esekeyd u-boot-utils tslib-calibrate tslib-tests
i2c-tools i2c screen rsync nfs-utils-client
directfb gdbserver directfb mtd-utils
rsvg pango

export IMAGE_BASENAME = "mini2440-image"

inherit image

Then all you have to do is source the script from wherever you put it:

source source-me.txt

and run bitbake:

bitbake mini2440-image

from the ~/OE/openembedded/ directory..

If you get an error trying to build a package try cleaning it:

bitbake -c clean INSERTPACKAGENAME

Then try and build the image again. Maybe you won’t have this problem. I guess it’s either because the checksum parser failed to build or my hdd is dodgy. It only happened once on binutils but worked fine after cleaning it.

A few hours later if all goes well you should have images in:


Obviously that directory depends on what you setup in the local.conf.

Good luck!

New hardware!

After breaking the z-axis connection on my first device I ordered a new KXPS5 accelerometer from crodnet on ebay. I really recommend this seller, he’s very cheap and sends things rapidly.

I quickly knocked together a circuit on veroboard and hooked up the base of a transistor to the freefall / motion interrupt pin to check it was working. It is remarkably sensitive, the LED flicks on if i drop my pen at one end of my desk when the device is at the other! I was quite pleased that everything was working well so i hooked it up to the I2C bus using the cable kit kindly supplied by Using I2C tools i was able to set registers and read acceleration vectors without any trouble so i’m pretty sure everything is working well. I was a bit worried about exceeding the bus capacitance at first.



It turns out that i can still use the old device if i rely on the internal low pass filter. I was thinking of doing this anyway and using a Kalman filter to process the output. First i need to write a device driver so i’ve rapidly being trying to learn C. So far i’ve got a very basic kernel module up and running on the mini2440 🙂

Building Angstrom

I’ve been meaning to put this up for a while. Providing nothing goes wrong the whole process is actually very easy! This is basically a rehash of the Angstrom webpage so you might prefer to follow that taking notes of the minor deviations below:

export OETREE="/home/doug/OE"
mkdir -p ${OETREE}

cd ${OETREE}
git clone git:// openembedded
cd openembedded
git checkout origin/stable/2009 -b stable/2009

To update the OE metadata simply:

cd ${OETREE}/openembedded
git pull

Now make the suggested script source-me.txt changing OETREE to suit your needs:

export OETREE="/home/doug/OE"

echo Setting up dev env for Ångström

if [ -z ${ORG_PATH} ] ; then
export ORG_PATH

if [ -z ${ORG_LD_LIBRARY_PATH} ] ; then



export LANG=C

echo "Altered environment for OE Development"

I also had to set:

sudo sysctl vm.mmap_min_addr=0

Then setup local.conf:

mkdir -p ${OETREE}/build/conf
cp ${OETREE}/openembedded/contrib/angstrom/local.conf ${OETREE}/build/conf/

Now edit ${OETREE}/build/conf/local.conf and add this to the end:

MACHINE = "mini2440"

Now download the mini2440 config file from openembedded. Put this in:


Now source the source-me.txt, go to the OE tree, check it’s up to date

source source-me.txt

cd ${OETREE}/openembedded

git pull - -rebase

Now build the images, you can build all of them or just one. I used the base image for running Qt but i also built the gpe image which worked nicely if you need it.

bitbake base-image ; bitbake console-image ; bitbake  x11-image ; bitbake gpe-image

Be prepared to saturate your internet connection, wait a long time and take up a lot of disk space!

The result ends up in:


You should have the image(s) in .jffs2 for flashing and .tar.gz for mounting using NFS.

Mini2440 cable kit and soldering LGA14!

The very kind people at were generous enough to send me a mini2440 cable kit! This will be much easier than chopping up 2.5″ IDE connectors! The kit has all the connections you could ever need and will certainly make things much easier!


After getting the DS1621 thermometer working on the I2C bus i now on plan on connecting something more complicated and very small! They probably won’t recommend it in the data sheet but you can solder LGA14 using a normal iron and some enamelled wire. My first attempt is below. Unfortunately i started with much thicker wire which subsequently pulled a pad off but the thinner 0.15mm stuff is fairly easy. Checking the connections with a multimeter revealed no short circuits.


The plan is try this again with the same device (without breaking it!) and then solder it to some veroboard to which i’ll connect one of my new cables 🙂

Compiling the kernel with DS1621 support

After building the temperature sensing I2C circuit i posted about before i compiled a kernel for the mini2440 which supported the DS1621 temperature sensor. Thanks to the existing kernel support this was remarkably easy.

All i had to do was edit /mini2440_defconfig in …/kernel/mini2440/arch/arm/configs and change line 1039 to:


I compiled the kernel using the script i posted here interrupting the process after the git clones to change the line above and then allowing it to continue. I then booted the mini2440 and the sensor module was immediately available under:


In this directory you have the following:

root@mini2440:/sys/devices/platform/s3c2440-i2c/i2c-adapter/i2c-0/0-0048# ls
alarms           name             temp1_max        uevent
driver           power            temp1_max_alarm
hwmon            subsystem        temp1_min
modalias         temp1_input      temp1_min_alarm

The output on the DS1621 is controlled by the temp1_min and temp1_max thresholds. By default it goes high when temp1_input < temp1_min. You can view the temperature by reading temp1_input and you can adjust temp1_min and temp1_max by echoing the required threshold to the file, for example:

root@mini2440:/sys/devices/platform/s3c2440-i2c/i2c-adapter/i2c-0/0-0048# cat temp1_input
echo 27000 &gt; temp1_min

In this configuration the DS1621 output is high and drives the base of my transistor which switches on an LED. As soon as i heat the sensor the temperature goes above temp1_min the LED turns off.

Although i have no purpose for this circuit it serves as a proof of concept for installing I2C devices on the mini2440.

Here’s another pic with the power light on but the output off:


SMD on veroboard was never meant to look nice!

Booting using NFS and TFTP (updated)

Rather than slowly wearing out your NAND flash you can boot the mini2440 over a network by loading the kernel using TFTP and the OS from an NFS share. This also makes it much faster to test changes. Using Fedora 11 you can use YUM to install tftp, tftp-server and nfs-utils.

yum install tftp tftp-server nfs-utils

I created a folder /home/doug/mini2440/root_fs and added the following line to /etc/exports to allow r/w access from 192.168.1.*:


..and extracted the Angstrom file system as root to /home/doug/mini2440/root_fs

You’ll need to edit /etc/xinetd.d/tftp to setup TFTP. Mine is posted below for reference, you at least need to set disable = no.

# default: off
# description: The tftp server serves files using the trivial file transfer
#    protocol.  The tftp protocol is often used to boot diskless
#    workstations, download configuration files to network-aware printers,
#    and to start the installation process for some operating systems.
service tftp
disable    = no
socket_type        = dgram
protocol        = udp
wait            = yes
user            = root
server            = /usr/sbin/in.tftpd
server_args        = -s /home/doug/mini2440/kernel
per_source        = 11
cps            = 100 2
flags            = IPv4

I then started the services :

/etc/init.d/nfs start

/sbin/service xinetd start

To automate these i think you can do:

chkconfig tftp on

chkconfig xinetd on

chkconfig nfs on

Next i edited the uboot environment. Use the command setenv to modify or add entries and savenev when you’re finished. I ended up with the following:

MINI2440 # printenv
bootargs_base=console=ttySAC0,115200 noinitrd
root_nand=root=/dev/mtdblock3 rootfstype=jffs2
root_mmc=root=/dev/mmcblk0p2 rootdelay=2
set_root_nfs=setenv root_nfs root=/dev/nfs rw nfsroot=${serverip}:${root_nfs}
ifconfig_static=run setenv ifconfig ip=${ipaddr}:${serverip}::${netmask}:mini2440:eth0
ifconfig_dhcp=run setenv ifconfig ip=dhcp
set_bootargs_mmc=setenv bootargs ${bootargs_base} ${bootargs_init} ${mini2440} ${root_mmc}
set_bootargs_nand=setenv bootargs ${bootargs_base} ${bootargs_init} ${mini2440} ${root_nand}
set_bootargs_nfs=run set_root_nfs; setenv bootargs ${bootargs_base} ${bootargs_init} ${mini2440} ${root_nfs} ${ifconfig}
bootargs=console=ttySAC0,115200 noinitrd init=/sbin/init mini2440=0tb ip= root=/dev/nfs rw nfsroot=
bootcmd=tftp;bootm 32000000

Note when you setenv you have to omit the = sign. Obviously you’ll want to change some of this to suit your network setup. Here my laptop is and is my pfsense box which is assigning to the mini2440 by DHCP.

When you boot the system uboot will download the kernel over TFTP and then mount the NFS share.

If you have DHCP on your network Angstrom should automatically get an IP. You can skip the rest in this case!

If you want a static address you can change /etc/network/interfaces. I simply changed dhcp to static for eth0:

iface eth0 inet static

And after this the system booted up fine. Lastly i have a note which says I deleted the symlink /etc/resolve.conf and replaced it with:

domain local
search local

Be warned that the the entire of above needs to be compliant with your firewall and selinux, it won’t work otherwise!

I found the following Links helpful:



U-boot NFS / TFTP boot

Cross compiling Qt-embedded 4.5.3

Cross compiling Qt was actually very easy. I used the same machine described in the mini2440 kernel post.  If you have a vanilla install of Fedora 11  it’s more than likely you’ll get some errors due to missing packages so check the list i posted if you can’t figure out which ones you need. This is what i did:

  1. Download the Qt source from Trolltech
  2. Untar the archive somewhere, i simply used the desktop
  3. Edit the file mkspecs/qws/linux-arm-g++/qmake.conf according to your toolchain. I have attached mine here as an example. I used the toolchain from OpenEmbedded.
  4. Now run the following commands within the Qt directory:
  • ./configure -embedded arm -xplatform qws/linux-arm-g++ -prefix /usr/local/Qt -qt-mouse-tslib -little-endian
  • gmake -j 2 (or however many CPUs you have)
  • sudo gmake install

The resulting ~74MB  will be located in /usr/local/Qt. At first i ran the library from an SD card using a system wide link but later i used NFS.

I ran the library using BusError’s mini2440 kernel and an Angstrom base image I cross compiled using OpenEmbedded apriori. In my next post i’ll describe how to compile Angstrom Linux for this purpose which also provides the toolchain i used here. Finally when i get access to my mini2440 i’ll explain how to use the examples and setup the touch screen which was a little fiddly.

Big thanks to Cor for his post on building Qt which i’ve relied on heavily here.

Controlling the mini2440 system LEDs and the EEPROM

This is pretty trivial but i thought i’d post it just incase. Using the mini2440 kernel by BusError the system LEDs are registered under /sys/devices/platform/s3c24xxled.X, where X is the LED number. LEDs 1-4 are located on the system board and LED 5 is the backlight. To control the devices you can do the following:

cd /sys/devices/platform/s3c24xx_led.5/leds/backlight

echo 0 > brightness #turns the backlight off

echo 255 > brightness #turns the backlight on

You can also choose from one of the available triggers, for example..

root@mini2440:/sys/devices/platform/s3c24xx_led.5/leds/backlight# cat trigger
none nand-disk mmc0 timer heartbeat [backlight] gpio default-on
root@mini2440:/sys/devices/platform/s3c24xx_led.5/leds/backlight# echo heartbeat > trigger

Will make your backlight flash on and off like crazy!

Unfortunately there is no PWM control to manage the brightness. This would have been really nice.

The EEPROM can be controlled in a similar way. You can access it in:


Data can be written by using the following command:

echo whatever you want > eeprom

The just do the following to read the memory:

cat eeprom