IRQ_DISABLED
assert(irq_counts[irq] == 0 || irq_counts[irq] == IRQ_DISABLED);
irq_counts[irq] = IRQ_DISABLED;
assert(irq_counts[irq] != IRQ_DISABLED);
irq_counts[i] = IRQ_DISABLED;
if (irq_counts[irq] == IRQ_DISABLED)