Interrupt Controllers: ARM GIC & x86 APIC

When to use

• Writing or reviewing IRQ handlers, request_irq/threaded IRQ setup, or irqchip drivers.
• Configuring trigger types (edge/level), priorities, masking, and EOI.
• Debugging lost, stuck, or spurious interrupts (IRQ storms, missed IRQ).
• Setting IRQ affinity/balancing (irq_set_affinity, CPU maps).
• MSI/MSI-X setup and interrupt remapping.
• Porting interrupt code between ARM (GIC) and x86 (APIC).

When not to use

• Cortex-M NVIC-specific code (see cmsis / embedded-interrupt-and-nested).
• Software interrupts/timers inside the scheduler (kernel-scheduler domain).
• Userspace signal handling.
• Low-level ISR latency tuning without controller interaction (perf domain).