Today I got an request by email to include support for integer conversion from YUV422 to RGB as descriped by Wikipedia. So I included it and did some style adjustments, too.

You can download it here: v4l2grab Version 0.2

To use integer conversion you have to compile with an additional

-DNTSC

for NTSC like conversion or

-DITU_R_INT

for ITU-R integer conversion. Both standars are explained in the referenced wikipedia article. The use of

-DITU_R_FLOAT

uses the previous floating point version of ITU-R which is default if no compiling options are specified. More information about compilation can be found on the original post.

The current version of V4L2grab can be found on github.

This sounded interesting, so I googled for some benchmark test to measure differences. I found nbench, which measures performance by executing some typical algorithms and compares them to a Pentium 90 based system. So I installed it and run on the i586 CHOST system, then rebuild it completely to i486 CHOST and run it again. The differences are not that huge, but on some algorithms they’re measurable:

The first 13 bars are the different algorithms. The main difference is on the string sort, which is heavily memory dependent. That last 3 rows are a index based on the algorithms. Here is main difference on memory index, as the normalized version shows very clear (positive values mean that i486 is faster):

As there is no significant disadvantage of the i486 CHOST, this seems to be the choice.

If anybody has other (free) benchmarks to suggest, please let me know.

Installating is very easy: Download the patch (GPIO drivers for AMD CS5535/CS5536 (Kernel 2.6.30-rc6)), patch it and compile the kernel:

wget http://www.twam.info/wp-content/uploads/2009/05/gpio.patch -O /root/gpio.patch
cd /usr/src/linux
patch -p1 < /root/gpio.patch

Now run kernel configuration and select

Device Drivers  --->
   [*] GPIO Support  --->
   [*]   /sys/class/gpio/... (sysfs interface)
   <*>   AMD CS5535/CS5536 (Geode Companion Device)

Compile the kernel and reboot. If you go to /sys/class/gpio there should be a file name gpiochip0. Now we can enable some pins and test them. By

echo 6 > /sys/class/gpio/export

we tell the kernel, that we want to use pin 6 from userspace. Pin 6 is connected to led. Now we configure pin 6 as an output by

echo out > /sys/class/gpio/GPIO6/direction

Now we can toggle the values by

echo 1 > /sys/class/gpio/GPIO6/value
sleep 1
echo 0 > /sys/class/gpio/GPIO6/value

ALIX.3D3: modeswitch pins

Notice, that the LED is connected to 3.3V, so setting value to 0 it will be lit. The other LEDs are connected to pin 25 & pin 27. On pin 24 is a switch connected. We can read the value by enabling the pin, setting it as an input and reading the value:

echo 24 > /sys/class/gpio/export
echo in > /sys/class/gpio/GPIO24/direction
cat /sys/class/gpio/GPIO24/value

As the pin has an internal pull up, it will show 1 if the switch isn’t pressed or installed. If you press the switch or connect to the metal pins, it will result in 0.

Don’t forget to unexport all pins after when you’re done:

echo 6 > /sys/class/gpio/unexport
echo 24 > /sys/class/gpio/unexport

Any feedback on the driver is welcome!

Sadly there is no ebuild for flashrom in portage, so Gentoo users (and maybe some other) have to build it on there own, but it’s quite easy. You need to install subversion, an open-source revision control system, first:

emerge -va subversion

As there is no portage package for flashrom, we need to install it somewhere. I installed it in /root/flashrom so it can be removed easily. You can achieve this by

cd root
svn co svn://coreboot.org/flashrom/trunk flashrom
cd flashrom
make

You can do an optional

make install

to install the binaries in /usr/local/sbin and install the man page. Now we should save our old BIOS. Running

flashrom -r /root/bios_save.bin

should display some info on the found chipset and flash chip:

Calibrating delay loop... OK.
No coreboot table found.
Found chipset "AMD CS5536", enabling flash write... OK.
Found chip "AMIC A49LF040A" (512 KB) at physical address 0xfff80000.
Reading flash... done.

If you have an image of the old installed BIOS you can check, if everything went right, by

diff /root/bios_save.bin /root/bios_old.bin

where /root/bios_old.bin is the old BIOS version, preferable found on the manufacturer’s website. Now we can update the BIOS. Download the new BIOS version (ALIX.3D3 can be found here) and run:

flashrom -wv /root/bios_new.bin

flashrom should print some information, a process status and after all a VERIFIED, if everything went right:

Calibrating delay loop... OK.
No coreboot table found.
Found chipset "AMD CS5536", enabling flash write... OK.
Found chip "AMIC A49LF040A" (512 KB) at physical address 0xfff80000.
Flash image seems to be a legacy BIOS. Disabling checks.
Programming page: 0007 at address: 0x00070000
Verifying flash... VERIFIED.

Now your BIOS should be updated. It’s time to plug (power) and pray.

Update: After writing a Gentoo Bug report, there is now an ebuild in portage. You can install it by

emerge -va flashrom

Here comes bonding (sometimes called (port) trunking or link aggregation) to play. It connects two ore more ethernet ports to one virtual port with only one MAC and so mostly one IP address. Wheres earlier only two hosts (with the same OS running) or two switches (from the same vendor) could be connected, nowadays there’s a standard protocol which makes it easy: LACP which is part of IEEE 802.3ad. Linux supports difference bonding mechanisms including 802.3ad. To enable bonding at all there are some kernel settings needed:

Device Drivers  --->
[*] Network device support  --->
<*>   Bonding driver support

After compiling and rebooting, we need a userspace tool for configuring the virtual interface. It’s called ifenslave and provided with the Linux kernel. You can either compile it by hand

/usr/src/linux/Documentation/networking
gcc -Wall -O -I/usr/src/linux/include ifenslave.c -o ifenslave
cp ifenslave /sbin/ifenslave

or install it by emerge if you run Gentoo Linux:

emerge -va ifenslave

Now we can configure the bonding device, called bond0. Firstofall we need to set the 802.3ad mode and the MII link monitoring frequency by

echo "802.3ad" > /sys/class/net/bond0/bonding/mode
echo 100 >/sys/class/net/bond0/bonding/miimon

Now we can up the device and add some ethernet ports:

ifconfig bond0 up
ifenslave bond0 eth0
ifenslave bond0 eth1

Now bond0 is ready to be used. Run a dhcp client or set an IP by

ifconfig bond0 192.168.1.2 netmask 255.255.255.0

These steps are needed on each reboot. If you’re running gentoo, you can use baselayout for this. Add

config_eth0=( "none" )
config_eth1=( "none" )
preup() {
	# Adjusting the bonding mode / MII monitor
	# Possible modes are : 0, 1, 2, 3, 4, 5, 6,
	#     OR
	#   balance-rr, active-backup, balance-xor, broadcast,
	#   802.3ad, balance-tlb, balance-alb
	# MII monitor time interval typically: 100 milliseconds
	if [[ ${IFACE} == "bond0" ]] ; then
		BOND_MODE="802.3ad"
		BOND_MIIMON="100"
		echo ${BOND_MODE} >/sys/class/net/bond0/bonding/mode
		echo ${BOND_MIIMON}  >/sys/class/net/bond0/bonding/miimon
		einfo "Bonding mode is set to ${BOND_MODE} on ${IFACE}"
		einfo "MII monitor interval is set to ${BOND_MIIMON} ms on ${IFACE}"
	else
		einfo "Doing nothing on ${IFACE}"
	fi
	return 0
}
slaves_bond0="eth0 eth1"
config_bond0=( "dhcp" )

to your /etc/conf.d/net. I found this nice preup part in the Gentoo Wiki Archive.

Now you have to configure the other side of the link. You can either use a Linux box and configure it the same way or a 802.3ad-capable switch. I used an HP Procurve 1800-24G switch. You have to enable LACP on the ports you’re connected:

HP Procurve 1800-24G LACP Configuration

Now everything should work and you can enjoy a 2 GBits (or more) link. Further details can be found in the kernel documentation.

Sometimes, there’s a need to tell the kernel explicitly to prior some process, bind some process to a special CPU and so on.

Changing process priorities is commonly known:

nice -n 10 make

runs the program make with a priority of 10 (-20 meaning most favorable and 19 least favorable scheduling). If you want to change a priority of a running program, renice is your choice.

schedtool

Nowadays multiprocessor machines get more and more in common. So it’s sometimes desirable to bind a process to one or more CPUs. This is done by schedtool, which is not part of common distros. You can install it on Gentoo by

emerge -va schedtool

schedtool allows you to view, and change the process CPU affinity. Try

schedtool PID

where PID is the process ID. For example, process 6702 of my system shows:

PID  6702: PRIO   0, POLICY N: SCHED_NORMAL  , NICE   0, AFFINITY 0x3

meaning it’s CPU affinity mask is 0×03. Each bit of the affinity mask corresponds to a CPU in the system and a bit value of 1 meaning this CPU is allowed to use. So, 0×03 = 0b00000011 means that CPU0 and CPU1 are allowed to use. You can change the CPU affinity by

schedtool -a AFFINITY_MASK PID

where PID is the process ID and AFFINITY_MASK the affinity mask (must be in hexadecimal) or a list of (decimal) comma separated CPU numbers. Be careful not to use affinity 0×00 especially on viral processes.

schedtool also allows the change of schedule policy for a single job. This is useful e.g. for long-running non-interactive jobs. You can enable the SCHED_BATCH policy for them by

schedtool -B PID

where PID is the process ID. Notice that you need a least kernel 2.6.16 for SCHED_BATCH support. There are different schedule policies for Real Time or Idle applications. See man schedtool for detailed information.

taskset

Another program for setting process’s CPU affinity is taskset. It’s included in util-linux-ng, which is part of most common distros. taskset is only capable of changing/viewing CPU affinity, not priorities or scheduling policies.

To view a process CPU affinity try

taskset -p PID

where PID is the process ID. For the same process as above my systems shows:

pid 6702's current affinity mask: 3

You can change CPU affinity easily by

taskset -p AFFINITY_MASK PID

where PID is the process ID and AFFINITY_MASK the affinity mask. If you wish the use a command seperated CPU list you have to

taskset -c -p CPU_LIST PID

where PID is the process ID and CPU_LIST the CPU list like 1,3,4-6.

Unlike schedtool taskset is capable of starting programs with a specific CPU affinity mask by

taskset AFFINITY_MASK COMMAND

where AFFINITY_MASK is the affinity mask and COMMAND and command to execute. Seed man taskset for detailed information.

First of all, I recommend installing Gentoo on a normal desktop to get to know the installing process, which is a bit different from graphical installers of mainstream distros. The Gentoo Handbook is a great documentation how this done.

To install gentoo, you have to boot a minimal or “rescue” linux usually from cd/dvd. I tried to convice the bios to boot from a usb cd-rom drive, but I hadn’t any success.

So I had to prepare a USB stick to boot from. There’s a nice tool UNetbootin which automatically copies ISO images to a usbstick and makes it bootable. I tried a lot with the Linux version of it but didn’t had any success regardless of which ISO image or USB stick I took. So I booted windows and tried it with this version. I had success on the first attempt, using the install-x86-minimal.iso from Gentoo and a 3 EUR SD-card Reader with a 4 GB SDHC card in it, formatted as FAT32 as the only partition (not in superfloppy mode).

If you’ve got a booting usb stick, insert it into a USB plug of the board, attach a USB keyboard and a monitor to the VGA port. Power on and press escape to select the boot menu. There should be an option for the usb stick if everything went fine.

Now the gentoo minimal system should boot and you can proceed with the usual installing (look into Gentoo Handbook for details). The AMD Geode LX800 cpu is a i586 cpu, so you have to install a i386, i486 oder i586 stage (i686 or amd64 won’t work!). I installed a i486 stage 3 and updated later to i586.

Partitioning should follow your preferences but don’t a forget a swap partition. 256 MB of RAM is not that much and gcc will not compile without!

I took

CFLAGS="-O2 -march=i486 -pipe"

for installation as the gcc version on the stage3 archive don’t support the geode march.

The rest of the installation is business as usual. I installed gentoo-sources for a optimized kernel and took this configuration here: ALIX.3D3 kernel-2.6.29-r2 config

After finishing installation and booting with the new kernel, it’s time to update the systems to i586. For this, at first update all packages to actual version, especially gcc to version 4.3. Afterwards it’s save to change

CFLAGS="-march=geode -Os -fno-align-jumps -fno-align-functions -fno-align-labels -fno-align-loops -pipe -fomit-frame-pointer"

and proceed with changing of the CHOST variable. There’s a nice tutorial here: Changing CHOST.

Now you should have a nice and optimized gentoo on your ALIX.3D3

Since Kernel 2.6.27 most of the USB webcams are supported through the Linux UVC drivers, which provides an Video4Linux2 Interface to those cams. We found some programs who claimed being able to grab JPEG images from V4L2 Cams, but most of them either didn’t compile, supported only V4L Version 1 or just brought up some other errors.

So I checked up the Video for Linux Two API Specification and found there in Appendix B a small sample of howto communicate with the Cam. I adapted it to our needs and included an converter from YUV colorspace to RGB. Finally I added some code to support the export of JPEG images.

You can download it here: v4l2grab Version 0.1

The whole program is written in C and only needs libjpeg to compile. There are different ways to communicate with the camera, if you want to support all, you should go best with:

gcc v4l2grab.c -o v4l2grab -Wall -ljpeg -DIO_READ -DIO_MMAP -DIO_USERPTR

If you compiled the program, you can get some images with:

./v4l2grab -o image.jpg

With -W width -H height its possible to adjust the size of the image. If the camera doesn’t support the resolution the programs adjusts it automatically and prints an information on stderr.

The current version of V4L2grab can be found on github.

In earlier times I used a commented bash script to setup the rules after booting, but using Gentoo nowadays there is a nice init script saving and restoring my tables. Using this I stopped commenting the firewall rules, but yesterday I found a very nice solution for this problem.

Iptables has a special “match” for comments. You have to enable it in your kernel config like

  [*] Networking support  --->
     Networking options
        [*] Network packet filtering framework (Netfilter)  --->
           Core Netfilter Configuration  --->
              -*- Netfilter Xtables support (required for ip_tables)
              <*>   "comment" match support

or as a module.

Then you’re able to add rules like

iptables -A INPUT -m state --state RELATED,ESTABLISHED \
  -m comment --comment "allow all established connections" -j ACCEPT

And if you list your rules you get something like

Chain INPUT (policy DROP)
target  prot opt source     destination
ACCEPT  all  --  anywhere   anywhere   state RELATED,ESTABLISHED
                                       /* allow all established connections */

It’s a pity that I never saw this in any iptables tutorials.

To get KMS running on my macbook, I installed the 2.6.29 with the following settings

  Device Drivers  --->
    Graphics support  --->
      <*> Direct Rendering Manager (XFree86 4.1.0 and higher DRI support)  --->
        <*>   Intel 830M, 845G, 852GM, 855GM, 865G (i915 driver)  --->
          i915 driver
          [ ]    Enable modesetting on intel by default

You don’t have to enable KMS by default. It’s possible to do this via i915.modeset=1 as a boot option.

After booting the kernel, drm should have detected your outputs and load inteldrmfb

[    1.905481] [drm] TV-15: set mode NTSC 480i 0
[    2.021462] allocated 1280x800 fb: 0x00fdf000, bo ffff88013eaf2900
[    2.094941] [drm] LVDS-8: set mode 1280x800 17
[    2.191879] Console: switching to colour frame buffer device 160x50
[    2.195013] fb0: inteldrmfb frame buffer device
[    2.195038] registered panic notifier
[    2.195059] [drm] Initialized i915 1.6.0 20080730 on minor 0

To use KMS within X11, I had to update the latest xorg-server, x11-libs and xf86-video-intel from the x11-overlay. In /etc/X11/xorgs.conf must

        Option          "AccelMethod"   "UXA"

set in the intel driver section.

Notice that output names may have changed, if you use a multimonitor setup oder xrandr. I had VGA,TV,LVDS,TMDS-1 prior to 2.6.29 and now it’s VGA1,TV1,LVDS1,DVI1.

Das Programm AICCU initialisiert die Tunnel und benötigt als Konfiguration lediglich SiXXs-Benutzername und Passwort sowie eine Tunnel Nummer. Das Programm gibt es als net-misc/aiccu als Ebuild für Gentoo.

Ist der Tunnel erfolgreich eingerichtet kann auch ein IPv6 Subnet beantragt werden und weitere PCs im Heimnetz ans IPv6 Netz zu bekommen. Der Gentoo-IPv6-Router-Guide erklärt wie man radvd und dhcpv6 konfiguriert.