Atmel Evaluation Kit AT91SAM9X25-EK AT91SAM9X25-EK Data Sheet
Product codes
AT91SAM9X25-EK
76
SAM9X25 [DATASHEET]
11054E–ATARM–10-Mar-2014
Figure 13-8. Internal Interrupt Edge Triggered Source
Figure 13-9. Internal Interrupt Level Sensitive Source
13.8.3 Normal Interrupt
13.8.3.1 Priority Controller
An 8-level priority controller drives the nIRQ line of the processor, depending on the interrupt conditions occurring on the
interrupt sources 1 to 31 (except for those programmed in Fast Forcing).
interrupt sources 1 to 31 (except for those programmed in Fast Forcing).
Each interrupt source has a programmable priority level of 7 to 0, which is user-definable by writing the PRIOR field of
the corresponding AIC_SMR (Source Mode Register). Level 7 is the highest priority and level 0 the lowest.
the corresponding AIC_SMR (Source Mode Register). Level 7 is the highest priority and level 0 the lowest.
As soon as an interrupt condition occurs, as defined by the SRCTYPE field of the AIC_SMR (Source Mode Register), the
nIRQ line is asserted. As a new interrupt condition might have happened on other interrupt sources since the nIRQ has
been asserted, the priority controller determines the current interrupt at the time the AIC_IVR (Interrupt Vector Register)
is read. The read of AIC_IVR is the entry point of the interrupt handling which allows the AIC to consider that the interrupt
has been taken into account by the software.
nIRQ line is asserted. As a new interrupt condition might have happened on other interrupt sources since the nIRQ has
been asserted, the priority controller determines the current interrupt at the time the AIC_IVR (Interrupt Vector Register)
is read. The read of AIC_IVR is the entry point of the interrupt handling which allows the AIC to consider that the interrupt
has been taken into account by the software.
The current priority level is defined as the priority level of the current interrupt.
If several interrupt sources of equal priority are pending and enabled when the AIC_IVR is read, the interrupt with the
lowest interrupt source number is serviced first.
lowest interrupt source number is serviced first.
The nIRQ line can be asserted only if an interrupt condition occurs on an interrupt source with a higher priority. If an
interrupt condition happens (or is pending) during the interrupt treatment in progress, it is delayed until the software
indicates to the AIC the end of the current service by writing the AIC_EOICR (End of Interrupt Command Register). The
write of AIC_EOICR is the exit point of the interrupt handling.
interrupt condition happens (or is pending) during the interrupt treatment in progress, it is delayed until the software
indicates to the AIC the end of the current service by writing the AIC_EOICR (End of Interrupt Command Register). The
write of AIC_EOICR is the exit point of the interrupt handling.
13.8.3.2 Interrupt Nesting
The priority controller utilizes interrupt nesting in order for the high priority interrupt to be handled during the service of
lower priority interrupts. This requires the interrupt service routines of the lower interrupts to re-enable the interrupt at the
processor level.
lower priority interrupts. This requires the interrupt service routines of the lower interrupts to re-enable the interrupt at the
processor level.
MCK
nIRQ
Peripheral Interrupt
Becomes Active
Maximum IRQ Latency = 4.5 Cycles
MCK
nIRQ
Maximum IRQ Latency = 3.5 Cycles
Peripheral Interrupt
Becomes Active