System Interface Unit
MPC885 PowerQUICC Family Reference Manual, Rev. 2
10-14
Freescale Semiconductor
10.5.3.1
Nonmaskable Interrupts—IRQ0 and SWT
Figure 10-9
is a logical representation of IRQ0.
Figure 10-9. IRQ0 Logical Representation
Table 10-8
describes the differences between IRQ0 and other IRQ interrupts.
SWT (software watchdog timer) interrupts behave similarly in that they jump to the system reset vector
(0x100). However, they are not affected by any interrupt controller registers.
Although NMI causes a jump to the system reset vector, no other reset action is taken. For information
about recoverability of NMI, see
Section 6.1.5, “Recoverability After an Exception.”
10.5.4
Programming the SIU Interrupt Controller
The SIU’s interrupt controller includes the SIU interrupt pending register (SIPEND), SIU interrupt mask
register (SIMASK), SIU interrupt edge/level register (SIEL), and SIU interrupt vector register (SIVEC)
registers. These are described in the following sections.
Table 10-8. IRQ0 Versus IRQx Operation
Functionality
IRQ0
IRQx
Exception Vector
0x100
0x500
Core input
NMI
External interrupt
SIMASK
Not used, except for enabling SIVEC
Used for masking
SIVEC
Not normally used. If used, SIMASK[IRQ0] must
be set.
Supplies the interrupt code so the core knows
the interrupt source.
MUX
Level
Edge
FF
Q
Q
R
MUX
Level
Edge
SIEL[ED0]
SIEL[ED0]
NMI
SIPEND[IRQ0]
IRQ0
SIPEND[IRQ0] = 1
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