2010 Microchip Technology Inc.
DS70141F-page 49
dsPIC30F3010/3011
5.4
Interrupt Sequence
All interrupt event flags are sampled in the beginning of
each instruction cycle by the IFSx registers. A pending
Interrupt Request (IRQ) is indicated by the flag bit
being equal to a ‘1’ in an IFSx register. The IRQ will
cause an interrupt to occur if the corresponding bit in
the Interrupt Enable (IECx) register is set. For the
remainder of the instruction cycle, the priorities of all
pending interrupt requests are evaluated.
If there is a pending IRQ with a priority level greater
than the current processor priority level in the IPL bits,
the processor will be interrupted.
The processor then stacks the current program counter
and the low byte of the processor STATUS register
(SRL), as shown in
Figure 5-2. The low byte of the
STATUS register contains the processor priority level at
the time, prior to the beginning of the interrupt cycle.
The processor then loads the priority level for this inter-
rupt into the STATUS register. This action will disable
all lower priority interrupts until the completion of the
Interrupt Service Routine (ISR).
FIGURE 5-2:
INTERRUPT STACK
FRAME
The RETFIE (Return from Interrupt) instruction will
unstack the program counter and STATUS registers to
return the processor to its state prior to the interrupt
sequence.
5.5
Alternate Vector Table
In program memory, the Interrupt Vector Table (IVT) is
followed by the Alternate Interrupt Vector Table (AIVT),
Table is provided by the ALTIVT bit in the INTCON2
register. If the ALTIVT bit is set, all interrupt and
exception processes use the alternate vectors instead
of the default vectors. The alternate vectors are
organized the same as the default vectors. The AIVT
supports emulation and debugging efforts by providing
a means to switch between an application and a
support environment without requiring the interrupt
vectors to be reprogrammed. This feature also enables
switching between applications for evaluation of
different software algorithms at run time.
If the AIVT is not required, the program memory
allocated to the AIVT may be used for other purposes.
AIVT is not a protected section and may be freely
programmed by the user.
5.6
Fast Context Saving
A context saving option is available using Shadow
registers. Shadow registers are provided for the DC, N,
OV, Z and C bits in SR, and the registers, W0 through
W3. The shadows are only one level deep. The
Shadow registers are accessible using the PUSH.S
and POP.S instructions only. When the processor
vectors to an interrupt, the PUSH.S instruction can be
used to store the current value of the aforementioned
registers into their respective Shadow registers.
If an ISR of a certain priority uses the PUSH.S and
POP.S
instructions for fast context saving, then a
higher priority ISR should not include the same
instructions. Users must save the key registers in
software during a lower priority interrupt if the higher
priority ISR uses fast context saving.
5.7
External Interrupt Requests
The dsPIC30F3010/3011 interrupt controller supports
three external interrupt request signals, INT0-INT2.
These inputs are edge sensitive; they require a low-to-
high or a high-to-low transition to generate an interrupt
request. The INTCON2 register has five bits, INT0EP-
INT4EP, that select the polarity of the edge detection
circuitry.
5.8
Wake-up from Sleep and Idle
The interrupt controller may be used to wake-up the
processor from either Sleep or Idle modes if Sleep or
Idle mode is active when the interrupt is generated.
If an enabled interrupt request of sufficient priority is
received by the interrupt controller, then the standard
interrupt request is presented to the processor. At the
same time, the processor will wake-up from Sleep or
Idle and begin execution of the Interrupt Service
Routine needed to process the interrupt request.
Note 1: The user can always lower the priority
level by writing a new value into SR. The
Interrupt Service Routine must clear the
interrupt flag bits in the IFSx register
before lowering the processor interrupt
priority, in order to avoid recursive
interrupts.
2: The IPL3 bit (CORCON<3>) is always
clear
when
interrupts
are
being
processed. It is set only during execution
of traps.
<Free Word>
0
15
W15 (before CALL)
W15 (after CALL)
S
tack
Grows
T
o
wards
Hig
her
Address
PUSH : [W15++]
POP
: [--W15]
0x0000
PC<15:0>
SRL IPL3 PC<22:16>