Hmm, I still can't make the interrupt controller work on an actual Raspberry Pi 4. The goal is to set up a timer that fires an interrupt (so that we can pre-empt a process). And it doesn't help that the GIC-400 interrupt controller has impenetrable documentation.
QEMU only supports the "legacy" interrupt controller, which should be equivalent to the ones in a RPi ≤ 3. So I put `enable_gic=0' in the config.txt and set up the "local timer" in the interrupt controller to fire repeatedly. This works for QEMU, but not on an actual RPi 4.
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