Datasheet

SAM9261 [DATASHEET]
Atmel-6062O-ATARM-SAM9261-Datasheet_21-Jun-16
280
If the interrupt source is programmed in level-sensitive mode and an active level is sampled, Fast Forcing results
in the assertion of the nFIQ line to the core.
If the interrupt source is programmed in edge-triggered mode and an active edge is detected, Fast Forcing results
in the assertion of the nFIQ line to the core.
The Fast Forcing feature does not affect the Source 0 pending bit in the Interrupt Pending Register (AIC_IPR).
The FIQ Vector Register (AIC_FVR) reads the contents of the Source Vector Register 0 (AIC_SVR0), whatever
the source of the fast interrupt may be. The read of the FVR does not clear the Source 0 when the fast forcing
feature is used and the interrupt source should be cleared by writing to the Interrupt Clear Command Register
(AIC_ICCR).
All enabled and pending interrupt sources that have the fast forcing feature enabled and that are programmed in
edge-triggered mode must be cleared by writing to the Interrupt Clear Command Register. In doing so, they are
cleared independently and thus lost interrupts are prevented.
The read of AIC_IVR does not clear the source that has the fast forcing feature enabled.
The source 0, reserved to the fast interrupt, continues operating normally and becomes one of the Fast Interrupt
sources.
Figure 26-10. Fast Forcing
26.7.5 Protect Mode
The Protect Mode permits reading the Interrupt Vector Register without performing the associated automatic
operations. This is necessary when working with a debug system. When a debugger, working either with a Debug
Monitor or the ARM processor's ICE, stops the applications and updates the opened windows, it might read the
AIC User Interface and thus the IVR. This has undesirable consequences:
 If an enabled interrupt with a higher priority than the current one is pending, it is stacked.
 If there is no enabled pending interrupt, the spurious vector is returned.
In either case, an End of Interrupt command is necessary to acknowledge and to restore the context of the AIC.
This operation is generally not performed by the debug system as the debug system would become strongly
intrusive and cause the application to enter an undesired state.
This is avoided by using the Protect Mode. Writing PROT in AIC_DCR (Debug Control Register) at 0x1 enables
the Protect Mode.
When the Protect Mode is enabled, the AIC performs interrupt stacking only when a write access is performed on
the AIC_IVR. Therefore, the Interrupt Service Routines must write (arbitrary data) to the AIC_IVR just after reading
it. The new context of the AIC, including the value of the Interrupt Status Register (AIC_ISR), is updated with the
current interrupt only when AIC_IVR is written.
Source 0
_
FIQ
Input Stage
Automatic Clear
Input Stage
Automatic Clear
Source n
AIC_IPR
AIC_IMR
AIC_FFSR
AIC_IPR
AIC_IMR
Priority
Manager
nFIQ
nIRQ
Read IVR if Source n is the current interrupt
and if Fast Forcing is disabled on Source n.
Read FVR if Fast Forcing is
disabled on Sources 1 to 31.