at91rm3400 ATMEL Corporation, at91rm3400 Datasheet - Page 111

• Manufacturer Part Number: at91rm3400
• Description: Atmel Advanced At91 Arm Microcontroller
• Manufacturer: ATMEL Corporation

Fast Forcing
1790A–ATARM–11/03
Note:
Another way to handle the fast interrupt is to map the interrupt service routine at the address
of the ARM vector 0x1C. This method does not use the vectoring, so that reading AIC_FVR
must be performed at the very beginning of the handler operation. However, this method
saves the execution of a branch instruction.
The Fast Forcing feature of the advanced interrupt controller provides redirection of any nor-
mal Interrupt source on the fast interrupt controller.
Fast Forcing is enabled or disabled by writing to the Fast Forcing Enable Register
(AIC_FFER) and the Fast Forcing Disable Register (AIC_FFDR). Writing to these registers
results in an update of the Fast Forcing Status Register (AIC_FFSR) that controls the feature
for each internal or external interrupt source.
When Fast Forcing is disabled, the interrupt sources are handled as described in the previous
pages.
When Fast Forcing is enabled, the edge/level programming and, in certain cases, edge detec-
tion of the interrupt source is still active but the source cannot trigger a normal interrupt to the
processor and is not seen by the priority handler.
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 Fast Interrupt Vector Register (AIC_FVR) reads the contents of the Source Vector Regis-
ter 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.
and masking or unmasking the fast interrupt depending on the state saved in the
SPSR.
The "F" bit in SPSR is significant. If it is set, it indicates that the ARM core was just about to
mask FIQ interrupts when the mask instruction was interrupted. Hence when the SPSR is
restored, the interrupted instruction is completed (FIQ is masked).
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