Aside - explicit reference to Raspberry Pi here:
https://opensource.apple.com/source/xnu/xnu-4903.221.2/osfmk...
EDIT: Eh, maybe not the copyright is quite old - perhaps more likely some internal test? Run ARM64 XNU tests on Raspberry Pis maybe? They are pretty cheap hardware with lots of ports.
It did turn out to be true that Apple was moving to run iOS (and later on, even APFS) all the way down to watch hardware, and later on the HomePod which is the functional successor to the audio features of the Airport Express.
Had they continued producing routers, it's all but guaranteed that they would be running firmware similar to the HomePod at this point.
The reason they would be building XNU for the bcm2837 however is probably much more "boring", like allowing various teams inside Apple to test some low level change being planned for the kernel, perhaps in the network stack, without the added hassle and potential for leaks that would result from using some other unreleased Apple platform to do it.
FreeBSD is a nice BSD platform. Darwin is kind of a weird mess, with Unix awkwardly mashed up with Mach and extra C++ frameworks (IOKit etc.) on top.
Was it just the cost of maintaining the certification? The fact that no other OS went down that route?
This file is evidence that Apple has been running iOS/MacOS on the Raspberry Pi 3?
Whether they had the full stack running—and how much of the stack is necessary for something to be deemed "macOS"—is up for debate.
- The memory subsystem is also a joke. 1 GB of slow LPDDR2 is the limit!?
- The boot process is absurd. A proprietary blob is loaded onto the GPU (!) from the SD card before everything else. An independent FOSS replacement boot stack project was started but not finished.
- And the firmware's support for network booting is very, very unreliable.
- There is a custom interrupt controller instead of the standard ARM GIC. (This was in fact one of the frustrations cited in the post about the open boot stack project's abandonment.)
- CPU crypto extensions (AES+PMULL/SHA1/SHA2) are absent. Other similar (4-core A53) SoCs (A64, RK3328) do have it.
- The GPU does not have memory protection. The VC4 driver does its best to try to validate shaders, but… LOL.
And here we're talking about Apple. They make their own SoCs. If they decided to get into IoT, they'd probably make a development platform based on one of their small chips they use in AirPods or whatever
