> Apple designed their own interrupt controller, the Apple Interrupt Controller (AIC), not compatible with either of the major ARM GIC standards. And not only that: the timer interrupts - normally connected to a regular per-CPU interrupt on ARM - are instead routed to the FIQ, an abstruse architectural feature, seen more frequently in the old 32-bit ARM days. Naturally, Linux kernel did not support delivering any interrupts via the FIQ path, so we had to add that.
> Apple designed their own interrupt controller, the Apple Interrupt Controller (AIC), not compatible with either of the major ARM GIC standards. And not only that: the timer interrupts - normally connected to a regular per-CPU interrupt on ARM - are instead routed to the FIQ, an abstruse architectural feature, seen more frequently in the old 32-bit ARM days. Naturally, Linux kernel did not support delivering any interrupts via the FIQ path, so we had to add that.
and many others
https://corellium.com/blog/linux-m1
It is on top of HN now https://news.ycombinator.com/item?id=25859907