Debian on iPhone Linux

NAND writing is now semi-reliable (although one has to be VERY careful not to interrupt the device in the middle of a write operation), but it is enough to have something akin to a full-functional OS, backed by non-volatile storage.

People interested in the project should be familiar with the myriads of Linux "distributions" floating around. An operating system consists of two major domains: one is the kernel, which is what manages the hardware, and one is the userland which contains things like shells and other UIs, package managers, etc. Software that help users install and run useful programs. Ubuntu is a popular distribution that I run on my personal machine. Android could also be considered a distribution (though I believe it has some apparently messy kernel patches).

I decided that Debian would be an interesting thing to try, since we would then instantly have a userland and a pool of ready-compiled applications. Using a slightly dated root filesystem here: http://lists.debian.org/debian-arm/2007/01/msg00034.html, a initrd and further kernel configurations were sufficient to get it to run. Thus, we can now compile programs for iPhone Linux on iPhone Linux. The process is rather slow due to the processor and inefficient NAND device driver (pending a real FTL), but at least theoretically, iPhone Linux is now self-hosting.

This should be pretty much enough for those who are more into the userland development side of things to come in, possibly using Debian as a base to build anything else (as I believe it is standard enough).

I will be offering instructions on how to get this all to work soon. The (modified for gadget serial terminal) rootfs is fairly hefty (around 130 MB), so I'm not sure how we'll handle distribution of that.

Porting drivers to Linux

We've made some progress on the USB gadget driver for Linux, and we're now running a generic serial gadget for communication. This implementation is important because USB is now a lot less laggy and things like ethernet over USB, etc., can eventually be supported, easing access.

We've also got pretty far with porting the NAND driver to Linux. Most of the read support is now there, and we've isolated the routines in the iPhone kernel where the raw hardware write occurs. CPICH and c1de0x are working on reversing it. Hopefully, it will be analogous enough to reads that it won't take a huge amount of time to work out.

This is different from reversing their FTL, however, which is a complicated slew of data structures, merge buffers and other exotic algorithms that take care of evenly distributing writes throughout the device and also making writes take less time.

I think reversing all of that would take too much time and effort. Instead, my proposal is to just reverse the hardware NAND writes. Instead of using a partition, we would have a loop-mounted root filesystem (similar to how Wubi is setup), with the root filesystem being a file on the Media partition. Since there's a non-empty file at that location, the FTL system, whatever it is, must create a one-to-one mapping from logical sectors to physical NAND pages. We can already read the mapping it creates (we have already reversed the read-side FTL code), and so all we have to do to alter the data is to write to the same pages we would've read from. Of course, this means that wear-leveling and bad block handling is not performed. However, if we use a filesystem that's aware of bad blocks and can wear-level (YAFFS or JFFS2), then it amounts to the same thing. The wear-leveling would then take place over the particular physical pages belonging to the rootfs image, rather than the entirety of the NAND. This would make the physical pages belonging to the rootfs image wear out a little faster than the rest of the NAND, but the actual effect of this should be inconsequential.

The additional benefit of this setup is that there's no repartitioning required, so setup is cinch. See this wiki document for specific proposed implementation details.

Donations...

A couple of people asked for a donate button of some sort. I hesitate because of the sudden complexity of things when money is involved. Here is what I think would be best:

• Donate your time and skills if you can rather than money.
• If you cannot do so, please consider sponsoring something we could directly use: Such as a USB serial cable (about $45 for parts from Sparkfun), or perhaps upgrading the Slicehost slice we're borrowing from pumpkin ($60 per month, though it would only be useful if we could get enough money for at least six months), used or broken devices for testing, etc. Or something like a pizza for one of our contributors on a late night hacking binge (we will distribute food donations on a round-robin basis =P)
• My paypal address is my gmail e-mail address (planetbeing). If you do make a donation, please specify exactly what it is for. A gigantic slush fund is something that I wish to avoid.
  

For the record, contrary to what was published by some media sources, the iphonelinux group is not associated with the group commonly known as the "iPhone Dev Team". I'm a member of the Dev Team, and other members sometimes lends assistance or advice, but this is an entirely separate project. The Dev Team does not accept any donations whereas this project tentatively will.

Updating and uninstalling openiboot

It's actually slightly problematic to use the "Update Firmware" feature of iTunes with openiboot installed, so I updated openiboot with an uninstall facility.

I uploaded the binaries and instructions necessary to update openiboot (and then uninstall it if you wish) to: http://www.iphone-dev.org/planetbeing/openiboot-uninstall.tar.gz

Linux on the iPhone!

I'm pleased to announce that the Linux 2.6 kernel has been ported to Apple's iPhone platform, with support for the first and second generation iPhones as well as the first generation iPod touch. This is a rough first draft of the port, and many drivers are still missing, but it's enough that a real alternative operating system is running on the iPhone.



What we have:

- Framebuffer driver
- Serial driver
- Serial over USB driver
- Interrupts, MMU, clock, etc.

What we have in openiboot (but hasn't been ported yet):

- Read-only support for the NAND

What we don't have (yet!):

- Write support for the NAND
- Wireless networking
- Touchscreen
- Sound
- Accelerometer
- Baseband support

The current userland we're using, in the interest of expedience, is a Busybox installation created with buildroot, but glibc works fine as well, and we're going to build a more permanent userland solution.

A demonstration video can be seen here: http://www.vimeo.com/2373142

Instructions here: http://www.iphone-dev.org/planetbeing/LINUX-README.txt

Download here: http://91.186.26.18/iphone/files/iphonelinux-demo.tar.gz (look for mirrors in the comments)

EDIT: The instructions are missing the step that you have to select openiboot console from the menu before performing the "sudo ./oibc" step. Just be aware you have to do that if it seems like you're not getting a response from the oibc client.

Project lead: planetbeing

Contributors: CPICH, cmw, poorlad, ius, saurik

If you're experienced with hacking/porting Linux and especially if you're experienced with porting Android, I'd definitely like to hear from you. Come chill in the #iphonelinux channel on irc.osx86.hu. Thanks. :)

EDIT: I was asked a couple times by people who wanted to donate (financially) to the project. I made a post discussing this possibility, if you are interested.

Poorlad's menu implemented; Porting issues resolved

Yesterday night, I merged in a branch I was working on for poorlad's menu. A version of that beautiful menu is now in Git. His menu included a version string at the bottom. We didn't have any way to keep track of versions and builds before, so this was actually a good idea that I had to implement. Because I didn't want to implement support for non-fixed width fonts, or add another space-consuming font, I just used the console font I was already using for that part. I also had to brighten the gradient on the bottom of the screen, since it was basically invisible due to gamma issues otherwise.

The border between the gradient and the "black" is clearly visible on my device. This is probably because of a gamma issue. When poorlad comes back, we can ask him to calibrate it more.

Otherwise, it looks pretty good! In order to make this possible, I added in stb_images.c, a great tiny little image library that can read PNG, JPEGs and even PSD files and does zlib decompression as an added bonus. This will be a great help if we decide to change things or need to add more stuff that consumes a lot of space. I also added in a basic function to perform alpha blending (albeit comparatively slowly).

Sadly, while I was busy making these changes, ius from IRC actually begun to implement poorlad's menu without me knowing about it, so we ened up duplicating each other's efforts. He was able to compile in zlib and libpng, but the cost was to inflate the final binary to 347 KB. Whereas taking out the old menu images, and adding small, compressed PNGs and the stb_images library instead actually made openiboot smaller than it was before! His decision to preblend the images, rather than attempt alpha blending on the device, was probably more optimal from a performance perspective.

Steven Troughton-Smith told me on Twitter that he has actually implemented his own boot menu as well. I'm not sure if he used the new PNG code or not, but the new code makes it pretty easy for a competent programmer to add in whatever menu they would like. I'd tell everyone to skin away, but we should keep as few wild branches of this project as possible, since everyone randomly installing openiboot just for kicks (especially a modified version) and then coming to us (read: me, ultimately) for support is something we don't have the resources to handle at this moment.

On the porting side, the issues with installation, optimizing NOR access on iPhone 3G, NAND access on a few devices all seem to have been fixed, so we can basically scratch the first two items off of the list I put up in the last post. I'm pleasantly surprised at how relatively easy it was.

Anyway, now for the kernel. Well, if I don't get distracted by writing to NAND.

Porting to iPhone 3G and iPod touch

Hey guys,

The lack of updates for the past few days is because many of you decided to visit us in IRC, thus enabling work to be done on porting openiboot to the iPod touch and the iPhone 3G (in particular because I don't have an iPod touch at the moment).

I'm pleased to report that everything now seems to be working on the iPhone 2G and the iPhone 3G (albeit NOR read/write on the iPhone 3G is unoptimized and is unacceptably slow). There is apparently an outstanding issue with the NAND ECC on some (?) iPod touchs, and also some people can't seem to actually install openiboot to NOR on both iPhone 2G and iPod touch. Unfortunately, the problem is that these things happen on devices that I don't have physical access to, and IRC is often a frustrating medium for communicating with testers. I'm confident these issues will be resolved soon, though.

So, current simultaneous projects:

1. Resolve openiboot porting issues
2. Implement poorlad's boot menu
3. Work on write support for FTL

After at least one of those things are done, we'll be working on the Linux kernel.