at91rm3400 ATMEL Corporation, at91rm3400 Datasheet - Page 109

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

Fast Interrupt
Fast Interrupt Source
Fast Interrupt Control
1790A–ATARM–11/03
2. The ARM core enters Interrupt mode, if it has not already done so.
3. When the instruction loaded at address 0x18 is executed, the program counter is
4. The previous step has the effect of branching to the corresponding interrupt service
5. Further interrupts can then be unmasked by clearing the “I” bit in CPSR, allowing re-
6. The interrupt handler can then proceed as required, saving the registers that will be
Note:
7. The “I” bit in CPSR must be set in order to mask interrupts before exiting to ensure that
8. The End of Interrupt Command Register (AIC_EOICR) must be written in order to indi-
Note:
The interrupt source 0 is the only source which can raise a fast interrupt request to the proces-
sor except if fast forcing is used. The interrupt source 0 is generally connected to a FIQ pin of
the product, either directly or through a PIO Controller.
The fast interrupt logic of the AIC has no priority controller. The mode of interrupt source 0 is
programmed with the AIC_SMR0 and the field PRIOR of this register is not used even if it
reads what has been written. The field SRCTYPE of AIC_SMR0 enables programming the
0x18. In the following cycle during fetch at address 0x1C, the ARM core adjusts
R14_irq, decrementing it by four.
loaded with the value read in AIC_IVR. Reading the AIC_IVR has the following effects:
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–
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routine. This should start by saving the link register (R14_irq) and SPSR_IRQ. The link
register must be decremented by four when it is saved if it is to be restored directly into
the program counter at the end of the interrupt. For example, the instruction SUB PC,
LR, #4 may be used.
assertion of the nIRQ to be taken into account by the core. This can happen if an inter-
rupt with a higher priority than the current interrupt occurs.
used and restoring them at the end. During this phase, an interrupt of higher priority
than the current level will restart the sequence from step 1.
the interrupt is completed in an orderly manner.
cate to the AIC that the current interrupt is finished. This causes the current level to be
popped from the stack, restoring the previous current level if one exists on the stack. If
another interrupt is pending, with lower or equal priority than the old current level but
with higher priority than the new current level, the nIRQ line is re-asserted, but the
interrupt sequence does not immediately start because the “I” bit is set in the core.
SPSR_irq is restored. Finally, the saved value of the link register is restored directly
into the PC. This has effect of returning from the interrupt to whatever was being exe-
cuted before, and of loading the CPSR with the stored SPSR, masking or unmasking
the interrupts depending on the state saved in SPSR_irq.
Sets the current interrupt to be the pending and enabled interrupt with the highest
priority. The current level is the priority level of the current interrupt.
De-asserts the nIRQ line on the processor. Even if vectoring is not used, AIC_IVR
must be read in order to de-assert nIRQ.
Automatically clears the interrupt, if it has been programmed to be edge-triggered.
Pushes the current level and the current interrupt number on to the stack.
Returns the value written in the AIC_SVR corresponding to the current interrupt.
If the interrupt is programmed to be level sensitive, the source of the interrupt must be cleared
during this phase.
The “I” bit in SPSR is significant. If it is set, it indicates that the ARM core was on the verge of
masking an interrupt when the mask instruction was interrupted. Hence, when SPSR is
restored, the mask instruction is completed (interrupt is masked).
AT91RM3400
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