<note warning>I'm not responsible for any bricked devices! Some actions described here may void your waranty! You have been warned!</note>

All information here relate to international version of Samsung Galaxy S3(GT-I9300). 99% of information can be found on intranets. These are just personal notes/summary on given topic and you might want to go and do your research/read up on the topic in detail.

Detailed information can be found at wiki, therefore I see no reason to duplicate it here.

• CPU - ARM Cortex-A9, quad-core, 1.4GHz
• GPU - ARM Mali-400 MP4

• heimdall
• Android SDK, resp. adb(search for “adt-bundle-linux-x86_64”, requires “compat” libs)

Knowing your Baseband version might come handy later when you want to flash stock ROM. It seems there is a stock ROM for each Baseband version, or at least by group. As I'm no expert, I'd not risk flashing stock ROM for Baseband version A to phone of version B.

How to find out this number?

• go into Settings → About device
• or you can use code *#1234# → AP/CP/CSC

PIT – the PIT file refers as ‘Partition Information Table’

You should download PIT as a guide and for backup if things go bad. What's there to study? Partition names, where which image belongs in case you need to flash stock ROM etc.

# heimdall download-pit --output my-sgs3.pit --no-reboot
# strings my-sgs3.pit
COM_TAR2Mx
BOOTLOADER
sboot.bin
TZSW
tz.img
mx.pit
MD5HDR
md5.img
BOTA0
BOTA1
efs.img
PARAM
param.bin
BOOT
boot.img
RECOVERY
recovery.img
RADIO
modem.bin
CACHE
cache.img
SYSTEM
system.img
HIDDEN
hidden.img
BACKUP
USERDATA
userdata.img
remained
\xUW;
Z3hzGO0
J       F+=y

Create backup before you flash anything. Boot into ClockworkMod recovery and do backup there as I'm not sure whether “backup” in 'droid would be sufficient.

• backup and restore → backup + create image zip → off-load via adb

This might save you some trouble, time and downloading later.

It seems like any 'droid based firmware doesn't like old stuff hanging around. And it seems like wipe data/factory reset mends this. Also, wipe cache and wipe dalwik if the former alone doesn't help. I'm not exactly sure whether you should wipe and reset before or after you flash.

• hold down Volume Up + Home + Power buttons
• red exclamation mark appears in the top left corner of the screen

• hold down Volume Down + Home + Power buttons
• or via 3x100K resistors in series connected to the two pins closest to the headphone jack on the USB port(unverified)

If you find yourself in a need to restore stock ROM like I did, use backup zip image you've created earlier. You did that, right? If you haven't created backup zip image like, for example, me, there is another way.

Find stock ROM based on your Baseband version. You can find these on intranets. They're being extracted from Samsung Kies software. And having said that, I don't understand why are these files being taken down under DMCA. So it might take you a while to find stock ROM for your SGS3.

After you've downloaded stock ROM, unzip it and unpack tar inside. Then compare files/images from stock ROM pack with your PIT file to see what goes where. Once you're clear on that, get SGS3 into ODIN mode and issue the following command(which is just an example!) and have fingers crossed:

heimdall flash \
  --BOOT boot.img \
  --BOOTLOADER sboot.img \
  --CACHE cache.img \
  --HIDDEN hidden.img \
  --RADIO modem.img \
  --SYSTEM system.img \
  --TZSW tz.img

I found couple posts related to B2G port on i9300, but it seems to me these efforts grinded to halt. More investigation (= clone B2G git and try to build it) is required.

Despite Samsung got S3 with Tizen officially certified, there is no public release and, pretty much, no other information related to Tizen on S3.

Information can be found at https://wiki.ubuntu.com/Touch/Devices/i9300. However, it seems there are some issues and phone isn't much of use on the phone part. This isn't much of a surprise.