Tag Archives: linux

Kernel develpoment on e60

Now that I have access to the serial console on Samsung e60 reader let’s build a new linux kernel for it.

The e60 reader has an ARM processor, to compile the kernel we need a cross compilation toolchain.
The first option is to use the one Samsung released with the other sources. It must work, however I don’t really like the idea to run binaries from unknown sources.
The second option is to build our own toolchain, we often have to do that for systems that requires patches on the compiler.
Here, Samsung’s binutils look like they were taken between 2.17 and 2.18 release (they are named 2.17.50 but are still slightly different from this snapshot) but they don’t seam to embed homemade patches. As for ggc I didn’t take time to check.
I choose to use the emdebian cross-development toolchain lenny version. (As the article in the french open silicium magazine #1 about FriendlyARM proposes to do).

Installing the cross-development toolchain on debian

First the archive keys:


sudo apt-get install emdebian-archive-keyring

Then we add a /etc/apt/sources.list.d/emdebian.list file with the following content:


deb http://ftp.uk.debian.org/emdebian/toolchains lenny main
deb-src http://ftp.uk.debian.org/emdebian/toolchains lenny main

The we update the package list to install the needed packages:


sudo apt-get update
sudo apt-get install libc6-armel-cross libc6-dev-armel-cross libstdc++6-armel-cross binutils-arm-linux-gnueabi gcc-4.3-arm-linux-gnueabi g++-4.3-arm-linux-gnueabi

That’s it ! We have now our cross-compilation toolchain installed from packages, so easy to update or remove.

The kernel sources

Samsung released it’s modified 2.6.29.4 version. By cloning the kernel 2.6.29.y git branch, I could quickly see that their changes applied well to the 2.6.29.6 version (the last in the branch).

In order to better sort the changes michel.s had splat them into several patches
(patchs on e60-open project). After a few trials I build a series file allowing to apply those patches with quilt or better to import them to a git branch with git quiltimport. The order I choose allows to drop easily some patches (the last ones).

One particular point on those patches is that some include binary files:

  • fs/rfs/*.o a proprietary journaling layer over FAT. If you want my point ov vue, we don’t need that. After all we have free journaling file systems available and linux is able to mount something else than FAT over USB…
  • drivers/usb/gadget/file_storage.o also the corresponding .c file was removed, the BSD/GPL license from the original code allows a binary distribution (however I didn’t check if Alan Stern’s name appears in the doc) but I’d have liked that Samsung give that source code.

U-Boot

Before compiling the kernel, we need the mkimage utility from U-Boot. Here, Let’s build the U-Boot released by Samsung, and let’s just copy the tools/mkimage to a location in our PATH (that’s the only install method I could find).


make smdkc100_config 
make CROSS_COMPILE=arm-linux-gnueabi-

cp tools/mkimage ~/bin/

Building linux

For the config, one of the patches includes a .config. That file is a copy of config_rfs so even without the previous patch, we can get Samsung’s config.

Finally we can compile!


make CROSS_COMPILE=arm-linux-gnueabi- CFLAGS="-march=armv4t -mtune=cortex-a8" CXXFLAGS="-march=armv4t -mtune=cortex-a8" ARCH=arm uImage

We can then load our kernel by following The kernel testing howto from e60-open project. To load the kernel we will need the following command:


sudo dnw arch/arm/boot/uImage

That’it, and it works ! Well almost, the kernel cannot find his modules. This will not be a big deal for the ones included in the sources (but the subject of a next post) but the /lib/modules/max14540.ko and lib/modules/dhd.ko modules are not included in the sources while reporting a GPL license to the kernel.

Missing source code

The Samsung Open Source Release Center website has a contact form, but it does not seam to work (I even booted my netbook on windows to try with IE8 without success). After browsing the french e60 forum I found their email address and mailed them, no answer so far (not even automatic). Let’s wait …

Conclusion

We can compile a kernel for the e60 reader without using the cross tools from Samsung.
There still some work to load modules as the one on the reader are copiled for 2.6.29.4 and our kernel does not want to load them. (I’ve already done a few tests but that will be a next posts’ topic.)
But without the missing sources it will be hard for us to best use our e60 reader.

Update: I got an answer from Samsung, they updated the released archive. I still have to look at it.

Serial console on Samsung E60 reader

Thanks to some discounts last January in France, I got a Samsung E60 reader.

A community started around the french forum (e60 – hardware.fr) and the google code (e60-open).

There are many information there especially on the serial console. I own an USB to serial adapter that uses LVTTL 3.3V signals (based on FTDI FT2232C) so I choose to connect on R232 and R233. But RXD (R232) is already connected to the MAX232 chip that shift LVTTL levels to serial levels, and it seams that this chip is styronger than my FTDI… So I removed R232 to connect me FTDI there. Remains to know on which PAD ? Luckily the first one I tried was the one: the one on the battery side.

A picture on my nice soldering:
E60 RS232 LVTTL 3.3V

That was it. I then followed the testing a kernel procedure thus loading the kernel image from the project’s SVN. And it worked ! (except that I had to unload the secbulk module, so it’s either me or it’s useless).

Next time, compiling and testing a Linux kernel.

First step in kernel development

I wanted to work on linux kernel from some time, but didn’t really know where to start. One day a wise man told me “a good way to learn is to do it! So get an USB device and write the driver for it.” I answered: “Well I didn’t thought of that, usually I’d use libusb for such cases.”

A USB device

Some days later, I didn’t find any nice device, but I thought, why not building it as well?
As I already told you, I’ve already hacked out an USB device: USBtinyISP. So I got back to the original code: usbtiny and I build myself a small device with 4 LED and 2 buttons:

My prototype's picture

I didn’t use and ATtiny, but an ATmega8 to keep more room for future improvements 😉 (The ATtiny2313 is already full with the USBtinyISP code).

And here is the schematic: (as picture, the gschem sources stay in git under the sch folder):

The schematic

Once the wiring done, some few lines of code based on the usbtiny sample, and that’s it: A firmware for the ATmega (in the root of the project).

Then I needed to test it, so back to the first idea, some code lines using libusb, available in the test, helped to improve the firmware 😉

Everything’s OK, let’s write a driver.

The Linux driver

Well I just followed some tutorials:

Finaly looking at the usbled.c file in Linux sources to get some more updates.

This build a module that adds the files leds and keys in the device folder that Linux creates in /sys/bus/usb/.

That’s it! I don’t know if you learned something, but I did learn a lot! 😉

All source code are available under GPL2 or GPL2+ on my gitweb: jvdg_usbgadget.git

As for the egocentric name, it’s just to avoid any name conflict. This has no mean to be integrated anywhere anyway. (The device uses an USB ID reserved to prototyping, so unusable for products…)