4.3.8.1.3 Interrupt Clearing and Setting

All interrupt sources programmed to be edge-triggered (including the FIQ in source 0) can be individually set or cleared by writing respectively the Interrupt Set Command register (AIC_ISCR) and Interrupt Clear Command register (AIC_ICCR). Clearing or setting interrupt sources programmed in Level-Sensitive mode has no effect.

The clear operation is perfunctory, as the software must perform an action to reset the “memorization” circuitry activated when the source is programmed in Edge-Triggered mode. However, the set operation is available for auto-test or software debug purposes. It can also be used to execute an AIC-implementation of a software interrupt.

The AIC features an automatic clear of the current interrupt when AIC_IVR (Interrupt Vector register) is read. Only the interrupt source being detected by the AIC as the current interrupt is affected by this operation. (See the section Priority Controller.) The automatic clear reduces the operations required by the interrupt service routine entry code to read AIC_IVR. Note that the automatic interrupt clear is disabled if the interrupt source has the Fast Forcing feature enabled, as it is considered uniquely as an FIQ source. (For further details, see the section ”Fast Forcing”).

The automatic clear of interrupt source 0 is performed when the FIQ Vector register (AIC_FVR) is read.