Posted by planetbeing on under clock timer, iphe, day clock, versis, linux kernel, cpu x86, boot menu, linux drivers, mmu, android, opti, whirl, wi fi, graft, spi, knowledge gained from, many things, timers, vic, clocks | 
I've been getting a lot of questions from people that seem to reflect a basic misunderstanding of what it takes to port an operating system onto a new platform. People seem to think that just by writing, say, a boot menu, means that we can stick Android or Windows or whatever onto a device because we can have a menu option for it.
Here's what it takes for an
operating system to run on a device:
- The code must be designed for the right CPU. (x86, ARM, PPC)
- The code must be able to interact with the hardware in the way it expects.
Now, there are versions of Linux compiled in ARM (which the iPhone uses), there are even versions of Windows Mobile that are compiled in ARM. Why can't I, then, just stick Windows Mobile or Android (or another flavor of Linux) onto the iPhone and give it a whirl?
Because the code cannot interact with the hardware! That is, there are no Linux drivers or Windows Mobile drivers for the hardware that's on the iPhone. We're not even talking about things like the wi-fi won't work or anything silly like that. We're talking about big things, like not being able to start because it doesn't uncompress itself into RAM properly. We're talking about freezing the first time it has to wait for something to happen because it doesn't know how to run the hardware clocks and timers (which is CRITICAL for computers) and doesn't know when to start again.
Thus , if I tried to take some distribution of Linux or Windows or whatever, stick it in memory and start it, absolutely nothing will happen. That's right: nothing. There will be no output because it doesn't know how to run the display, or the USB, or serial. It probably won't even get to the first line of code that tells it to output something because so many things are broken.
So how can we get Linux to boot on the iPhone?By teaching it how to run the hardware. We take the knowledge gained from getting that boot menu to display and graft it into the Linux kernel. It took an unbelievable amount of devices just to get the boot menu display: clock, timer, vic, mmu, spi, i2c, gpio, system controller, pmu, nor, uart, usb, lcd, buttons. Some of those may seem obvious to you, some work in the background to support the other devices. But all of those had to be reverse engineered and all of them will have to transplanted into the Linux kernel to even get something half-assed booting.
If all of those devices were required to get something as simple as boot menu up, can you imagine what would happen if you tried to boot an operating system that did not know how to run ANY of those devices?
We cannot modify the Windows Mobile kernel because it's closed source, and so there's no way to get it to run on the iPhone.
The critical misunderstanding, I think, is that people think somehow that the OS "sits on top" of the boot menu, and talks to the hardware through the boot menu. Therefore, you can have an "emulation layer" that lets Windows or Linux or whatever talk to the hardware, without having to alter Windows or Linux itself. This is completely false. An operating system, by definition, has direct access to the hardware. Nothing sits between it and the hardware. Once iBoot has loaded the iPhone OS, you can go ahead and wipe it clean from the NOR and the OS will keep running as usual. It's not "running", it's not used or loaded in any way except during the boot process.
The iPhone will never run Windows Mobile directly (virtualization would be possible albeit it would crawl on the iPhone). It will run Linux once we write the drivers for it based on our knowledge of the hardware. Android uses the Linux kernel, though they do modify it to a certain extent. Since the only really hardware dependent parts of an OS is in the kernel, presumably once we install the necessary drivers, Android will run just as well as Linux runs. However, not having even looked at Android's source yet, I really don't have a truly educated opinion at the moment, but let's just say that it's one of this project's primary goals.
Sorry this is so long, but intelligent explanations tend to be long.
P.S. Another question people ask a lot is how long will it take. I can't truly give a good answer to that, because it's sort of dependent on the schedules of the people who work on it, and it also depends on how fast it'll take to write the Linux drivers, and how many unexpected problems crop up. It could go really unexpectedly fast, or we could hit a roadblock. I think outside observers, just reading the commit logs and reading the blog has as much information as I do on how fast things are progressing, so you're free to come up with your own conclusions on how long it will take.
Tagi: clock timer, iphe, day clock, versis, linux kernel, cpu x86, boot menu, linux drivers, mmu, android, opti, whirl, wi fi, graft, spi, knowledge gained from, many things, timers, vic, clocks
Posted by planetbeing on under linux kernel, iphe, bootmenu, muscle work, different numbers, source tree, deci, ftl, ipod touch, filesystem, screenshot, ports, lt, linux |
Amazingly enough, the FTL_Read stuff from last night was pretty much correct! After that, it was relatively trivial to port over the HFS+ code I've already written (which was in pure C... finally that [fail] design decision has been vindicated =P).
As you can see in the screenshot below, with the latest Git revision, you can browse the filesystem from openiboot!
Next on the list is to port openiboot over to the iPod touch and iPhone 3G. It's probably just a matter of putting in different numbers for the GPIO ports, but we'll see.
After that, I will implement poorlad's bootmenu (which everyone seems to like).
After that, well... We have pretty much all the devices now, so we'll start looking at the Linux kernel. If you're a Linux kernel guy who would be willing to help (preferrably you have experience porting Linux to new ARM platforms), please leave a comment here. I can do most of the muscle work, but it'd be nice if someone can show me how to set up the source tree properly for the new port.
Tagi: linux kernel, iphe, bootmenu, muscle work, different numbers, source tree, deci, ftl, ipod touch, filesystem, screenshot, ports, lt, linux
Posted by planetbeing on under linux kernel, simultaneous projects, boot menu, iphone, nand, ftl, 2g, iphe, ipod touch, hey guys, 3g, few days, resolve, peoe, linux |
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.
Tagi: linux kernel, simultaneous projects, boot menu, iphone, nand, ftl, 2g, iphe, ipod touch, hey guys, 3g, few days, resolve, peoe, linux
Posted by planetbeing on under th project, iphe, kernel tree, linux kernel, google, secd, helping hands, repo, source tree, hardware support, idroid, new hardware, repositories, repos, different things, newcomers, sdk, 3g, r2, irc |
We've gotten a tremendous response -- far more than I've actually anticipated before the release. I would like to thank the community for their interest. The amount of support and enthusiasm that was displayed was truly humbling to someone used to cynicism about this project.
The thing I'm most excited about is the fact there are now many developers working on several different things... a pretty big change from when I was hacking on the source tree virtually alone. There are developers actively working on the first generation iPod port, the iPhone 3G port, and a second-generation iPod touch port and things are moving much more quickly than I've anticipated. With so many helping hands, I'm sure that we can get these ports to production quality.
To coordinate our efforts, I've setup a series of git repositories on GitHub. You can clone the Android tree using Google's repo tool thus:
repo init -u git://github.com/planetbeing/platform_manifest.git -b android-sdk-1.6_r2-iphone
This command populates the majority of the tree from the main Android kernel.org repositories, with any changed project from my tree.
git://github.com/planetbeing/kernel_common.git branch android-2.6.32-iphone is our kernel tree. It is included in the main repo checkout as well.
git://github.com/planetbeing/iphonelinux.git as always is our openiboot/bootloader tree. New hardware support will be trialled there and then ported into the Linux kernel.
A fellow with the nickname of "konaya" on IRC has volunteered to administer a website for us at
http://www.idroidproject.org. We can use the wiki to document iPhone Linux/iDroid and the forums to provide help to newcomers. We also have a developer mailing list (please ask in IRC if you wish to get added to that).
Tagi: th project, iphe, kernel tree, linux kernel, google, secd, helping hands, repo, source tree, hardware support, idroid, new hardware, repositories, repos, different things, newcomers, sdk, 3g, r2, irc
