AN2109 Freescale Semiconductor / Motorola, AN2109 Datasheet - Page 47

• Manufacturer Part Number: AN2109
• Description: MPC555 Interrupts
• Manufacturer: Freescale Semiconductor / Motorola

8 Conclusion
1. Save Machine
Context, SRR0:1
2. Set MSR[RI]
3. Save Other Context
4. Determine Interrupt
Source
5. Branch to Interrupt
Handler
6. Restore Context
7. Return to Program
Total Number of
Although this document mainly concentrates on explaining how interrupts work on the MPC555, addi-
tional conclusions can be made. An important system design issue is proper planning of not only map-
ping interrupts but deciding what needs to be saved in a context switch. When measuring system
performance, the overhead associated with different contexts can vary dramatically.
Table 21
amples in the document and extrapolations for additional registers.
Instructions
ISR Step
illustrates interrupt service routine overhead in terms of number of instructions based on ex-
Table 21 Overhead Summary: Number of Instructions for Different ISRs
Assembly Routines
Freescale Semiconductor, Inc.
Example 2
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6
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7
6
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Rev. 0, 26 July 2001
MPC555 Interrupts
Go to: www.freescale.com
Assembly and C
Example 3
ISR Type
Routines
18
25
49
6
1
6
2
1
ISR Saves all GPRs
Example 3 + 20
other gprs (r2,
r13:31) saved/
restored
38
45
89
6
1
6
2
1
ISR Saves all GPRs
fprs, fpscr saved/
other gprs, all 31
Example 3 + 20
and FPRs
restored
MOTOROLA
157
72
79
6
1
6
2
1
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