INTERRUPT PRIORITY CONTROL WITHIN A NESTED INTERRUPT SYSTEM

A data processing system 2 having a nested interrupt controller 24 supports nested active interrupts. The priority levels associated with different interrupts are alterable (possibly programmable) whilst the system is running. In order to prevent problems associated with priority inversions within nested interrupts, the nested interrupt controller when considering whether a pending interrupt should pre-empt existing active interrupts, compares the priority of the pending interrupt with the highest priority of any of the currently active interrupts that are nested together.