AN2109 Freescale Semiconductor / Motorola, AN2109 Datasheet - Page 39

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

Freescale Semiconductor, Inc.
7.3.4 Example 4: ISR Using C Only – One Interrupt Source
Summary: This example shows how to implement an interrupt exception entirely in C.
Operation: This differs mainly from Example 3 in that no assembly language is used other than macros
in a C function. Also, only a simple check of one interrupt source is done by the interrupt service.
The files used are:
main.c: adds “Ext_ISR” function as the interrupt handler
exceptions.s: not used in this example! Context save/restore and interrupt and level testing done in C.
makefile: Added the Diab compiler option switch –Xnested-interrupts
link file: used etas_evb.lin as in other examples
Using C to write complete interrupt service routines is compiler dependent. How it is done, if at all, may
differ among compiler vendors. In addition, implementations using C++ can differ from C implementa-
tion within a compiler vendor. This example was done using the Diab Data compiler.
Stack Frame: Using the pragma statements and –Xnested-interrupt compiler option, the same regis-
ters were saved on the stack as in example 3. Hence the stack size was the same.
MPC555 Interrupts
MOTOROLA
Rev. 0, 26 July 2001
39
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