Figure 3-1 State Of The Stack When Irqa Is Serviced - Motorola DSP56600 Manual

Table 3-1 Implicit Stack Activity (Continued)
Triggered by Instruction or
Activity
exit DO loop
BRKcc (condition true)
immediately
The next example shows loop and subroutine nesting. Figure 3-1
shows the state of the stack at the time the fast interrupt is executing
(label I_IRQA, that enters execution when PC = $000529). The first
DO instruction pushes the existing data on LA and LC (0 and
$FFFFFF, respectively, in this example).
SP

Figure 3-1 State of the Stack When IRQA Is Serviced

Note: A fast interrupt does not effect the stack. Only long
interrupts (that have a subroutine call) push data into the
stack. Had IRQA been a long interrupt, another push would
have been done, the saved values being SSH:$529 (PC) and
SSL: $C18300 (SR). The different values of the LF and FV bits
in SR are saved as the nesting proceeds (no loop, finite loop,
infinite loop).
MOTOROLA Optimizing DSP56300/DSP56600 Applications
Condition
High
$C00300 (SR)
$109 (PC)
$0 (LA) $FFFFFF (LC)
$520 (PC)
$C00300 (SR)
$6 (LC)
$530 (LA)
$525 (PC)
$C08300 (SR)
Implicit Stack
Actions Taken
PC: = LA + 1;
SR: = SSL
SP: = SP – 1
LA: = SSH, LC: = SSL
SP: = SP – 1
Low
0
1
2
3
4
5
6
15
AA0833
Program Control
The Hardware Stack
3-5