7 functional description, 1 interrupt source control – Rainbow Electronics AT91CAP9S250A User Manual
Page 386
386
6264A–CAP–21-May-07
AT91CAP9S500A/AT91CAP9S250A
30.7
Functional Description
30.7.1
Interrupt Source Control
30.7.1.1
Interrupt Source Mode
The Advanced Interrupt Controller independently programs each interrupt source. The SRC-
TYPE field of the corresponding AIC_SMR (Source Mode Register) selects the interrupt
condition of each source.
The internal interrupt sources wired on the interrupt outputs of the embedded peripherals can
be programmed either in level-sensitive mode or in edge-triggered mode. The active level of
the internal interrupts is not important for the user.
The external interrupt sources can be programmed either in high level-sensitive or low level-
sensitive modes, or in positive edge-triggered or negative edge-triggered modes.
30.7.1.2
Interrupt Source Enabling
Each interrupt source, including the FIQ in source 0, can be enabled or disabled by using the
command registers; AIC_IECR (Interrupt Enable Command Register) and AIC_IDCR (Inter-
rupt Disable Command Register). This set of registers conducts enabling or disabling in one
instruction. The interrupt mask can be read in the AIC_IMR register. A disabled interrupt does
not affect servicing of other interrupts.
30.7.1.3
Interrupt Clearing and Setting
All interrupt sources programmed to be edge-triggered (including the FIQ in source 0) can be
individually set or cleared by writing respectively the AIC_ISCR and AIC_ICCR registers.
Clearing or setting interrupt sources programmed in level-sensitive mode has no effect.
The clear operation is perfunctory, as the software must perform an action to reinitialize the
“memorization” circuitry activated when the source is programmed in edge-triggered mode.
However, the set operation is available for auto-test or software debug purposes. It can also
be used to execute an AIC-implementation of a software interrupt.
The AIC features an automatic clear of the current interrupt when the AIC_IVR (Interrupt Vec-
tor Register) is read. Only the interrupt source being detected by the AIC as the current
interrupt is affected by this operation. (
See “Priority Controller” on page 389.
) The automatic
clear reduces the operations required by the interrupt service routine entry code to reading the
AIC_IVR. Note that the automatic interrupt clear is disabled if the interrupt source has the Fast
Forcing feature enabled as it is considered uniquely as a FIQ source. (For further details,
The automatic clear of the interrupt source 0 is performed when AIC_FVR is read.
30.7.1.4
Interrupt Status
For each interrupt, the AIC operation originates in AIC_IPR (Interrupt Pending Register) and
its mask in AIC_IMR (Interrupt Mask Register). AIC_IPR enables the actual activity of the
sources, whether masked or not.
The AIC_ISR register reads the number of the current interrupt (see
) and the register AIC_CISR gives an image of the signals nIRQ and nFIQ driven on
the processor.
Each status referred to above can be used to optimize the interrupt handling of the systems.