Introducing the Developer Transition Kit
Introducing the Developer Transition Kit
In my last post, I talked about how dosdude1 shipped out one of the few Apple silicon DTKs that he was able to repair to Stella and I. This blog post is mainly talking about the hardware itself, some of its quirks, what we've been doing with it, and where we are taking it in the future!
Update on Dec. 17th, 2024
Well, this is a surprise. My first update to this blog post is also probably going to be the last.
Yesterday, I made the decision to restore the DTK to a fresh copy of 11.2.3 - moving the important stuff I wanted to keep track of to my Samsung T7, booting it into DFU mode, and doing a simple restore with idevicerestore.
As early as December 5th, there was a report on bilibili of a DTK being unable to activate, with the same symptoms of one with bad SysCfg entries for serial number and MAC addresses. Due to the nature of this, dosdude1 was assisting in hopefully fixing the bad entries. However, this was not the case.
After the restore was completed on our DTK, I entered the Apple ID email and password that the unit was locked to, and rebooted it as there was no error - "Your Mac is activated." This began a loop of booting the DTK into recoveryOS, connecting to the internet, and having it say it was activated... even though it is not.
It is pretty much confirmed at this point - after discussing it with dosdude1, someone in contact with the bilibili user, and people in the Hack Different Discord server - that this issue is caused by Apple's activation servers refusing requests from ADP3,2. Due to the nature of Apple silicon security and its boot process, this means that our DTK is (likely permanently) out of commission a lot earlier than we were expecting.
This may be the end of the line for using the DTK as a computer, but I haven't completely finished my work with it. In a future blog post, and with a lot of help from others, I will be delving deep into Apple's activation mechanism and hopefully pinpoint the needle that struck our DTK's heart.
ADP3,2
The DTK's story starts with the SoC: T8027. The public-facing name for it is Apple A12Z Bionic, which is just a renamed A12X that has all of its GPU cores enabled. Other than some board strapping and configuration differences, as well as the 16GB of LPDDR4X over the 6GB found in the iPads, it's the same SoC with all of the same features - ANE, AVE and AVD, Vortex/Tempest, M12, so on and so forth.
With this SoC, as well as other changes to its board in order for it to work "enough", Apple created a modified 2018 Mac mini motherboard that was (almost) completely compatible with the casing from it. This familiar, yet completely new experience provided developers in the Universal App Quick Start Program the tool they needed to build and run their Universal2 apps (and test their existing ones in Rosetta) before M1 officially launched.
That being said...
Stella and I don't have anything other than the DTK board itself, connected to power using a USB-C PD board we soldered directly to some of the pins on the PSU connector.
With the new board came new identifiers: production unit DTKs have a boardconfig of J273aAP and a model identifier of ADP3,2. This configuration is supported (at least, officially) with 20A5299w until 20E5186d - as builds 20E5196f and later do not have the firmware for the DTK, and later builds began the process of removing the kernel and some supporting extensions.
At least now, 20D91 is the newest version still signed for the DTK (Apple unsigns macOS betas after a certain period of time, so the compatible 20Exxxx builds can't be installed via DFU/Recovery Mode.) For simplicity, we've chosen to stick with this - but I am still doing research to find out if it can be taken farther.
A (buggy) Apple silicon Mac
As a pre-production unit that was never supposed to be used after the leasing period was up, the DTK has many behaviors that stand it out against other Macs with Apple silicon. Some notable inclusions pulled from the DTK Release Notes PDF (that I have noticed in its usage) include:
Hardware
T8027 doesn't support 4K memory pagesize
This one made quite a splash with apps like Chrome and Firefox needing to be modified in order to support the 16K pagesize that the A12Z supports. Apps that still use 4K memory pages, such as WINE, continue to not work.
T8027 doesn't support Hypervisor.framework
Apple silicon SoCs before T8101 and T8103 (A14 Bionic and M1 respectively) do not have hardware virtualization capabilities at all. Emulators like QEMU continue to work, however, due to their ability to emulate rather than virtualize.
T8027 has a power-hungry SMC
Due to how the SMC is usually powered by a battery that is much larger than a simple BR1632A, Apple opted to put three of them onto the DTK's board - and they would still only last around 6 months. However, the DTK works just fine without them (other than losing its clock when power is lost, and automatically starting itself when power is reconnected.)
ADP3,2 doesn't support force shut down via the power button
This seems to only apply to the power button on the case of the DTK - the pads for PWR_ON_OFF directly on the board can be bridged directly to initiate a forced shutdown.
Speaking of the power button, did you notice the red light coming from the left side of our DTK? dosdude1 managed to swap on production DTK parts into a development DTK board - so we have the fancy PMU_RESET, PWR_ON_OFF, and FORCE_DFU buttons and LEDs. Super helpful for debugging (although the pads are free even on production boards!)
ADP3,2 is the only 2020 Mac to not support Thunderbolt
Snazzy Q actually covered this in his video, noting the lack of Thunderbolt retimers on the board. This leaves the DTK to only have USB-C at 10Gbps speeds, with support for DisplayPort Alt Mode.
Software
ADP3,2 takes a bit to initialize its framebuffer
Upon boot, the DTK tends to flash a black screen once or twice, and then show the end of the Apple logo progress bar as it boots into macOS (or directly shows the Startup Manager screen if you are choosing to boot into SFR.) Occassionally, the DTK will output a magenta screen like a panicking device with A12 or later:
ADP3,2 doesn't support installing macOS to another volume
In the PDF, Apple says this:
At least in my usage of the DTK, you can still use an InstallAssistant package to install macOS to another volume. I haven't tried macOS Recovery though.
ADP3,2 doesn't support HDCP or FairPlay-protected content
Apple Music, Apple TV, Safari, and other protected content apps don't work properly on the DTK. However, FairPlay seems to work enough to at least grant iOS apps running.
Rosetta 2 uses only the Vortex cores
This is partly why the first DTK Geekbench 5 scores show about a 52% performance loss compared to a 2020 iPad Pro with the same SoC.
Aside from the above issues (and many others I haven't talked about from the PDF), there are new issues that come from using T8027 in an age where T8103 is the oldest officially supported device capable of running macOS: ARM ISA differences. There are many projects that will crash on the DTK because they were compiled with instructions that T8027 doesn't support. Needless to say, I'm keeping a macOS Big Sur VM around on my server to deal with these issues, which included cross-compiling rust.
The current status of our DTK
Before I brushed off the DTK after our move, I was using a 2014 Mac mini to do the server tasks I needed out of macOS - not to mention, it was a birthday gift from a kind soul in OCLP. As a bit of a test to see how well the DTK would do in its place, I spent a few weeks moving the 2014's tasks into the DTK. I have been almost completely successful with that job:
The only things that truly remain are my GitHub Actions setup, and possibly recompiling CPython. Other than that, it performs well, efficiently, and even without a fan!
The future status of our DTK
The DTK is an interesting specimen, and it's also the first Mac with Apple silicon to be dropped from support. With aging hardware on an aging instruction set, with aging software that is starting to lose app support (and WebKit has already broken,) we have been exploring the possiblity of running newer macOS releases on the DTK. Currently, I have been able to gather the following:
- Build
20E5186dhas the kernel, kexts, and firmware forT8027andJ273aAP- Build
20E5172ifirmware has a bug that breaks both USB-A ports - Build
20E5186dfirmware possibly has a bug that breaks USB-C display output - Build
20E5196fand later release notes say that DTK support is unavailable
- Build
- Build
20E5196fhas the kernel and kexts intact forT8027, but none of the firmware forJ273aAP - Build
21A5284ehas the kexts forT8027, but no kernel forT8027or any of the firmware forJ273aAP- Build
21A5268hmight not have the kernel as well
- Build
- Build
22A5266rdoes not have some required kexts, kernel, or any of the firmware- An assumption as was probably removed earlier (I just haven't confirmed when - I'll update this post when I find out!)
The possibility of running a newer version of macOS is still up in the air, and needs more digging to be confirmed one way or another (however, based on past trends, it seems unlikely at the moment.)
Recently, iOS jailbreak developer and fellow reverse engineer Nick Chan has been working on porting Linux to checkm8 devices. He's been doing a really great job, and has also asked for our help in testing his patches on our DTK. You can see his work here:
We're excited to help and see how this ends up.
There's of course the last remaining pieces to put together in order for the 2014 Mac mini's transition to be complete - and I'll be tackling those for a while. In the meantime and after those are fixed, the DTK will be serving some of its life as a (somewhat) stable-enough server to host those macOS things that I needed.
Oh, and we'll also make sure to get the right parts to give it a proper case, PSU, IO plate, etc.
Final thoughts
Having a DTK in 2024 is a very interesting experience, and it's been a bit of a test of my macOS hacking knowledge - but I have learned quite a bit from it, and plan to continue doing so. I also compiled my own JDK for it (to solve some Minecraft server crashes), and will probably be adding a new server to mc.thatstel.la later on for fun 😉
Happy hacking,
- Eva