Datasheet

SAM9261 [DATASHEET]
Atmel-6062O-ATARM-SAM9261-Datasheet_21-Jun-16
276
26.7.2.4 Internal Interrupt Level Sensitive Source
Figure 26-9. Internal Interrupt Level Sensitive Source
26.7.3 Normal Interrupt
26.7.3.1 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).
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.
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.
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.
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.
26.7.3.2 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.
When an interrupt of a higher priority happens during an already occurring interrupt service routine, the nIRQ line
is re-asserted. If the interrupt is enabled at the core level, the current execution is interrupted and the new interrupt
service routine should read the AIC_IVR. At this time, the current interrupt number and its priority level are pushed
into an embedded hardware stack, so that they are saved and restored when the higher priority interrupt servicing
is finished and the AIC_EOICR is written.
The AIC is equipped with an 8-level wide hardware stack in order to support up to eight interrupt nestings pursuant
to having eight priority levels.
MCK
nIRQ
Maximum IRQ Latency = 3.5 Cycles
Peripheral Interrupt
Becomes Active