Started to play with the Galaxy S (GT-I9000) phone

For many years I'm on a more or less consistent hunt for finding a reasonably open and free mobile phone. This started in 2004 with OpenEZX, has continued with Openmoko, project gnufiish and has resulted in a bit of peeking and poking in the Palm Pre. However, none of those projects ever had the success I was hoping for:

  • OpenEZX was never really finished, and only for the 1st generation phones (A780) by the time they were long end of life
  • OpenMoko Neo1973 and FreeRunner were a great project, and they are still the most open+free mobile phones that ever existed. However, they're GPRS only and the hardware is even more outdated now then it was when we created it.
  • gnufiish was an attempt of running software from the Openmoko days (such as on some E-TEN glofiish phones. However, we never could make the SPI-based modem communication work from our re-engineered Linux driver :(
  • Palm Pre is an interesting device, in that Palm provides easy root access, does not attempt to lock the device down with cryptographic signatures and provides full recovery flashing tools by means of WebOS Doctor. But once again, the proprietary communication protocol with the 3G Modem was the big blocker item for using real custom software and not the WebOS stuff they ship.

So I've constantly been on the watch for new devices that are coming out. Most of the phones you can buy in recent years are either running proprietary software like Windows Mobile, Symbian, Apples iPhone-OSX - or they run Android but then use some integrated Qualcomm Smartphone-on-a-chip product. The problem with the latter (from a Free Software point of view) is that Qualcomm is very secretive about their products, does not provide any kind of public documentation, and the ever-increasing integration between application processor and baseband processor makes it more difficult to run custom software on them.

The Samsung Galaxy S (GT-I9000) seemed like a good candidate to me, for several reasons:

  • Samsung does not use cryptographic signature techniques and gaining root as well as flashing the AP software is relatively easy
  • The phone is based on a traditional separate application processor (AP) and baseband processor (BP) design. The AP is a Samsung S5PC110, the BP is some Qualcomm MSM6xxx.
  • High-end hardware, with the S5PC110 running at 1GHz and 512MB RAM
  • Samsung provides excellent "GPL source code offers" containing the Linux kernel used in their firmware - including detailed instructions in how to build it. Also, many of the drivers are included under GPL, such as drivers for all the integrated peripherals of the SoC, some custom components like the USB multiplexor ASIC, etc. as well as the driver for the dual-ported RAM between the AP and BP for the 3G Modem communication
  • The Android RIL shipped by Samsung contains lots of debugging/decoding/dumping code that can make reverse engineering the AP/BP protocol.

So right now I'm in the exploration phase, making myself familiar with the bootloader, the flashing process, the userspace ABI of the custom (GPL licensed) kernel drivers, etc. It's a fairly pleasant experience so far, and I now have a debootstrap'ed Debian lenny on an additional ext2 partition on the SD card. This provides me with an actually useful userland I can chroot() into, such as lsof, strace, ltrace, tcpdump, etc. to do some more exploration of the phone.

The only real ugliness on the software side so far is the use of proprietary Samsung filesystems (RFS/TFS4). The only reason those filesystems existed, as far as I can tell, was to run legacy filesystems like FAT on top of raw NAND or OneNAND flash. This is mainly necessary if you want to export e.g. a FAT partition via USB Mass Storage to a Windows PC. However, the GT-I9000 doesn't have any OneNAND, but only an internal moviNAND (basically a SD-Card in a BGA package that you can solder on the board). MMC/SD cards already include the wear leveling algorithm, so there is absolutely no point (from what I can tell) in running the RFS/TFS4 stack.

In fact, in several forums people are complaining about the slow I/O performance of the Galaxy S, and they have a much better performance when using ext2/ext3 directly on that moviNAND device.