Just a quick update. I am hoping to begin a "soft release" of the T4 bootloader chips next week, and a full release later in February.
A "soft release" means we are going to limit the per-person quantity to about 5-10 chips, and we will request that you communicate directly with us about your experience using the chips. There are 2 main reasons for a this "soft" release.
1: Initially we'll have very little bootloader specific documentation and PCB design guidance, only the schematics and files published for Teensy 4.0 & 4.1.
2: Robin & I are working on logistical changes in how we will program these chips, mainly focusing on removing all manual human steps between the programming and printing of the label we put onto the packaging material. We're also trying to limit possibility for human error between your clicks on the website and which programmer hardware we use. Today we sell only 2 chips, and they are physically very different so it's easy to tell them apart. Once we add the T4 bootloader, we'll be shipping the same physical MKL02 chip (no MKL04 option for T4) but with different firmware. This process stuff may be overly paranoid, but I want to be very certain we can't accidentally send T3 bootloader chips when T4 are ordered, and vise versa.
The soft release is meant to make prototype quantities of these chips available for your project, while we work on documentation and redesigning our material handling process. When we later move to full release, you'll be able to buy any quantity and as now the policy will be "no questions asked" about your custom PCB design (unless of course you want help troubleshooting... that's always done on this forum).
Here are some random technical details...
The fuse initialization is working, including the ethernet mac address / USB serial number. This has been the main technical obstacle. I can confirm it is solved.
Initialization of the flash isn't working yet, but I plan to have that by next week.
The 15 second restore program has been updated to automatically detect which flash chip your board uses (rather than distinct versions of the restore process, as we use now on Teensy 4.0 vs 4.1).
The bootloader chip will *not* lock your IMXRT fuses or flash chip. If you want to burn additional fuses, you will be able to do so. Certain fuses settings can permanently brick your board. We'll publish a program you can run to lock your fuse settings & flash restore to prevent any "bricking" possibility, as we have on Teensy 4.0 & 4.1 (but then you forever are locked out of turning on security or other fuse settings which affect startup).
Initially the booloader will not support encrypted firmware or HAB authentication, but some provisions have been included so we can (hopefully) add this support with a software update in the future.
A simple hardware diagnostic using patterns of red LED blinks is also planned, but not yet implemented. This is the last major piece to go into the bootloader before a soft release. If your hardware works, then you'll never use this feature. But if something is wrong, rather than "dead board", you'll get a series of LED blinks to tell you what the bootloader thinks is wrong with your PCB. The T4 hardware is significantly more complex than T3, and the T4 bootloader has some speed optimizations which make its behavior more complicated than T3 (eg, Reset isn't held low while Program is low), so this diagnostic can hopefully help when things don't go as planned.
I know the wait has been very long & frustrating. We're almost there. Please, if you want to chat, discuss here, but DO NOT send a private email. When we're ready for the soft release to begin (very likely sometime next week) I will post about it here. So please subscribe to this thread to get notified when chips are ready.