WARNING!!

WARNING! Everything here is completely unsupported. Use everything at your own risk. The tools here can very easily kill your camera and cause other problems. The author takes no responsibility or liability for anything that may arise as a consequence of using this software. USE THESE TOOLS AT YOUR OWN RISK.

Introduction

EVERYTHING HERE IS MEANT FOR ADVANCED USERS who have a hard-bricked Hero2 / H3 Black camera (as in, the camera will not turn on at all) and who have no other choice but to throw the camera away. If you can get warranty support from GoPro instead, BY ALL MEANS USE IT. But don't try to do some experimental stuff on your own and THEN try to get warranty support - once you start doing anything experimental to the camera (including ANYTHING written here), you have voided your warranty.

Some forum users have gotten these tools to work as a debrick method for their Hero2 cameras - more information can be found here: http://goprouser.freeforums.org/booting-a-hard-bricked-hero2-camera-over-usb-experimental-t11626.html

Hero3 Black thread: http://goprouser.freeforums.org/booting-a-hard-bricked-hero3-black-camera-over-usb-danger-t14791.html

USB Command Mode

These are extremely unofficial and highly experimental tools for booting a Hero2 / Hero3 Black camera using the built-in USB command mode.

To enter the built-in USB command mode, you can do the following:

1. Disconnect USB from camera
2. Remove battery
3. Insert battery
4. Press and HOLD the Shutter button
5. Plug in USB
6. Press the Power button
7. Release the Shutter button

There might not be anything showing on the screen when the Power button is pressed. If the charging LED was on, it might turn off. Otherwise, the camera will still "look" completely dead. But, the camera should enumerate as a USB device with a VID/PID of 4255:0001 (for Hero2) or VID/PID of 4255:0003 for the Hero3 Black. If so, we are in business. At this point, it is possible to send simple commands over USB. They are:

• Read from an arbitrary 32-bit word by physical address
• Write to an arbitrary 32-bit word by physical address
• Leave USB command mode and jump to specified physical address

These commands can be used to initalize the memory controller, load arbitrary code into RAM, and execute it.

The code that may be loaded could be of our own creation entirely, or it can be one or more sections of the the original GoPro firmware (which may have been unpacked with https://github.com/evilwombat/gopro-fw-tools). So in theory it should be possible to load the HAL section and the bootloader (or the HAL and the RTOS section) to the camera and jump to it, in an attempt to resume an interrupted firmware update. Or, it may be possible to load a Linux kernel that was modified for running directly on the camera (unlike the existing kernel on the camera, which runs in a thread on the RTOS).

However, when loading Linux or the RTOS, we still need to load a portion of the BLD bootloader to perform basic HW initalization (like serial), etc. Another problem is that before the camera software runs, the BLD bootloader loads the HAL section and makes some modifications to it, presumably to relocate the HAL to a place where the Linux kernel and the RTOS can get to it (since the HAL code does not seem to be position-independent). Without these modifications, the raw HAL section found in the HD2-firmware.bin (or HD3.03-firmware.bin) file is not usable.

So, to load and execute anything interesting, such as Linux or the RTOS, we need to do the following things:

• Load the BLD bootloader (for things like serial init)
• Load a slightly modified (fixed-up) HAL
• Load the thing we want to run (RTOS or Linux, and possibly an initrd)
• Patch the BLD bootloader with an instruction to jump to our code rather than trying to boot normally.

I am not able to include the BLD and modified HAL binaries directly in the repo, but there is a tool to extract the binaries (and perform the HAL fix-ups) from the v312 HD2-firmware.bin file (or the v300 HD3.03-firmware.bin file for the Hero3 Black). Regardless of which RTOS version or Linux kernel we are trying to load, the BLD must come from the v312 version of the HD2-firmware.bin file, since the offsets and modifications that we make are specific to this version. See "Preparing the necessary bootstrap files" below for how to do this. The HAL comes from the HD2-firmware.bin or HD3.03-firmware.bin depending on the type of camera, but we still use the BLD from the Hero2 firmware to get the hardware going, regardless of camera type.

Compiling and Dependencies

For Windows, there are pre-built EXE files included, so there is no need to compile anything.

For compiling on Linux, the gpboot program requires libusb-1.0.0 to interact with the camera, so you will need to install the libusb-1.0.0 development files before compiling. On an Ubuntu system, you can do this with the following command:

$ sudo apt-get install libusb-1.0.0-dev

Once that is installed, you can build gpboot and prepare-bootstrap with a simple make command:

$ make

A warning about permissions

On some systems, you may need to add some kind of a udev rule to make the camera accessible by non-root users. Or, you could run gpboot with the 'sudo' command.

Windows Version

An even more experimental (and even less tested) but pre-built Windows version of prepare-bootstrap and gpboot is included here. These should operate like the Linux version (hopefully). Since Windows insists on having a specific driver for each USB device, I've included a quick "driver" for the camera when it is in command mode. This driver was made with Zadig.exe (see here: http://www.libusb.org/wiki/windows_backend) but I know very little about Windows and its drivers or how they work. Still, you should be able to open a Windows command prompt and use prepare-bootstrap.exe and gpboot.exe as described here. Miraculously, when running gpboot.exe --linux, the USB/Ethernet device created by the camera does in fact get recognized by Windows, but I had to unplug/replug USB to the camera after Linux was booted to make sure the network was fully working. For anyone interested, the Windows version was built using MinGW / MSYS.

If the included Windows driver gives you problems (or isn't signed, etc), you should be able to use Zadig.exe to make and install your own driver. The Hero2 USB ID is 4255:0001 and the Hero3 Black uses 4255:0003. Zadig.exe might even try to auto-detect the first "unknown device".

Preparing the necessary bootstrap files

To prepare the BLD and modified HAL, get the v312 HD2-firmware.bin file (if you have a Hero2) or the v300 HD3.03-firmware.bin file (if you have a Hero3 Black) and execute the following command:

prepare-bootstrap HD2-firmware.bin

• or - prepare-bootstrap HD3.03-firmware.bin

This will produce the necessary BLD and HAL files. Now gpboot will have the files it needs to bootstrap the camera. Again, this prepare-bootstrap commands MUST be run on the v312 (or v300 for H3B) firmware update files, regardless of what you are actually trying to load and boot in the end.

To actually boot the camera, you can use the 'gpboot' command.

The gpboot tool supports five loading modes. They are:

• Load bootloader (for Hero2 only)
• Load RTOS (for Hero2)
• Load RTOS (for Hero3 Black)
• Load Linux (for Hero2)
• Load Linux (for Hero3 Black)

Loading the Bootloader (BLD) only on the Hero2

gpboot --bootloader

This will load the BLD (and the pre-modified HAL) and jump into the bootloader. If everything else in the camera is okay, the camera should boot normally from this point (and you can use some FW update method to reflash the real bootloader in flash if it is somehow damaged). If you have serial connected to the camera, you can short the TX/RX pins to drop into the bootloader console prior to running this command. This option only applies to the Hero2 camera.

Loading the RTOS on the Hero2

gpboot --rtos rtos_file

This is probably the most "useful" booting method, but it is also risky. This will load the bootloader, modified HAL, and the specified RTOS file to the camera. The HAL / RTOS will be loaded at high addresses, along with a small relocate.bin file that knows to copy them where they need to be (in case the bootloader tries to overwrite the low memory for some reason). The bootloader will be patched in RAM to jump to the relocate.bin file rather than booting normally, to make sure it does not try to load some corrupted / damaged version from flash for whatever reason.

To actually get the RTOS files for the Hero2 camera, see https://github.com/evilwombat/gopro-fw-tools for a utility that can pull them out of existing HD2-firmware.bin image. The RTOS image is NOT the HD2-firmware.bin file in its entirety, but is actually a section inside this file. Since there are several firmware versions available, there are several RTOS images you can use. In general, it seems like a good idea to try to use the RTOS image from the firmware that you were trying to install when the camera got bricked. So, if you were trying to downgrade from v222 to v124, it makes sense to use the RTOS from the v222 firmware. But, I don't have enough data to say "what works best". To save you the trouble of running the FW parser, the following DD commands should be able to extract an RTOS image from an existing firmware file. Note that each command is specific to the firmware version, and using the wrong command with the wrong firmware file will result in a useless RTOS image.

If you want the RTOS from the v124 HD2-firmware.bin file:
$ dd if=HD2-firmware.bin skip=213248 conv=notrunc of=rtos_v124.bin count=6344704 bs=1

If you want the RTOS from the v198 HD2-firmware.bin file:
$ dd if=HD2-firmware.bin skip=15862016 conv=notrunc of=rtos_v198.bin count=6246400 bs=1

If you want the RTOS from the v222 HD2-firmware file:
$ dd if=HD2-firmware.bin skip=15866112 conv=notrunc of=rtos_v222.bin count=6250496 bs=1

If you want the RTOS from the v312 HD2-firmware file:
$ dd if=HD2-firmware.bin skip=15870208 conv=notrunc of=rtos_v312.bin count=6258688 bs=1

(Also keep in mind that v198, v222, and v312 firmware files have an
 'alternate' RTOS image as well - this is section_3 if you use
 fwunpacker, but I do not know what the difference between the main and
 the alternate images is).

If done correctly (and if you are lucky), the camera will boot up to the point that it will be execute RTOS commands from autoexec.ash on the sdcard, which could possibly be used to restore the camera to a working state. Keep in mind that sometimes something goes wonky with the A:\ drive on the RTOS, so it may be necessary to change directory from A:\ to D:\ in autoexec.ash before doing any interesting commands ( cd d:\ ).

I do not have an exact autoexec.ash sequence that will reflash the camera to a working state that works 100% of the time, but perhaps the autoexec.ash on gopro's website is a good start. Keep in mind that 'reboot' from autoexec.ash WILL NOT WORK if the camera is booted using the USB mode, meaning that for an update to finish, you might have to boot the camera using USB several times, with a delay of a few minutes before you turn off the camera and boot again, to let the camera "do its thing". This applies to performing updates as well, since the camera does "naturally" try to reboot once or twice during the update process (which again, won't work in this mode and you may have to do the 'reboot' by hand).

Loading the RTOS on the Hero3 Black

gpboot --h3b-rtos h3b-v300-rtos-patched.bin

This is probably the most "useful" booting method, but it is also risky. This will load the bootloader, modified HAL, and the specified RTOS file to the camera. For the Hero3 Black, the necessary RTOS file (h3b-v300-rtos-patched.bin) is generated by prepare-bootstrap, so there is no need to ue fwunpacker to create it (like we would need to do on the Hero2). The RTOS file gets patched to get around an unfortunate "feature" of the RTOS, where it tries to detect why it was booted, and shut down if there isn't a good reason. I guess this is needed if the RTOS was woken up by the wifi button or something, so it could turn on wifi and shut itself down again. Since the RTOS isn't really expecting to be booted over USB, it will detect the USB connection and then go into charging mode (instead of booting up), which is not very useful for debricking. So, we patch the RTOS file a little bit to ignore the bootup reason and just boot up anyway.

If you run this option, the Hero3 BLD, HAL, and RTOS will be loaded in memory, and the BLD will be patched to jump to our code instead of trying to read the RTOS from flash. We actually load another small file - evilbootstrap.bin. This file is just a small delay program that will blink the front red LED a few times and delay for a few seconds before jumping to the RTOS. The reason for loading this little delay is to give the user the opportunity to disconnect USB from the camera after the loading is complete, but before the RTOS starts running. If we don't do this, the RTOS will detect the USB connection and go into USB storage mode, rather than booting normally, which is not very useful. So, as soon as the RTOS loading gets to 100% and the red light starts blinking, you can unplug USB and the RTOS will try to boot within a few seconds. I expect the RTOS to be largely non-functional, since the DSP won't be loaded or running, but the RTOS might in theory be able to read the update.cmd file off the sdcard, or autoexec.ash

Loading Linux on the Hero2

gpboot --linux

This is probably the most advanced booting method, and the least useful. This command will load a pre-build Linux kernel (zImage) and a pre-built initrd (initrd.lzma) to the camera and boot them. The front LED should show a heartbeat pattern, and the camera should show up as a newly-detected USB Ethernet device. Once that happens, you can telnet to the camera on address 10.9.9.1 and hopefully get a little Linux shell. This may allow you to examine the state of the flash (also, cat /proc/mtd) and be able to do linux commands interactively. It is my hope that this can be a useful method to restore the flash on a camera that is otherwise totally wiped, but at the moment there is no known way to reflash the camera from within Linux that has worked. But, I haven't really tried this all that much. I did include 'nanddump' and 'nandwrite' into the busybox build, and they might come in handy (just be CAREFUL!). How the state of the flash relates to the CRCs in the partition table (PTB, also mtd1) is still not quite clear to me, either. There should also be kernel messages and a shell on the camera's serial port, at 115200 baud. The sdcard slot should be working as well, with the card being accessible via /dev/mmcblk0 (or /dev/mmcblk0p1, etc).

The kernel commandline options are hard-coded into gpboot.c, and if you are advanced enough that you want to change them, you can modify the file and rebuild :). If you want to build your own kernel, see sources/sources.txt. The kernel here is basically the kernel that was posted on gopro's website (http://gopro.com/support/open-source) with some modifications to make it actually compile, and some fixes. See sources/ for the patches applied to the kernel (on top of gopro's tarball). There should be a kernel config file in there as well. There is also a busybox config file, but I did not modify busybox (and you can get the source from busybox.net - see sources.txt).

Loading Linux on the Hero3 Black

gpboot --h3b-linux

This is essentially the same as the Hero2 Linux method described above, only it will load a kernel (zImage-a7) which works on the Hero3 Black. Recent updates have allowed the Hero3 Black to be booted without relying on Hero2 firmware, which was a long-overdue fix. Thanks to forum user 'narcoticrex' for mailing me a bricked Hero3 Black, which allowed me to dig deep enough to make this possible.

Why did I use LZMA as the compression method over the more widely-used GZIP? It seems to result in smaller files, which means shorter times needed to load the stuff over USB.

Well, that's that - have fun, be careful, and again, do everything at your own risk, and don't blame me for anything that goes wrong. But I hope someone can find this stuff useful, and can make a reliable hard-debrick method.

-- evilwombat