Interrupt Handling
6-25
Run-Time Environment
6.5 Interrupt Handling
As long as you follow the guidelines in this section, you can interrupt and return
to C code without disrupting the C environment. When the C environment is
initialized, the startup routine does not enable or disable interrupts. Interrupts
are disabled if the system is initialized via a hardware reset. If your system
uses interrupts, you must handle any required enabling or masking of inter-
rupts. Such operations have no effect on the C environment and are easily
incorporated with asm statements or by callling an assembly language func-
tion.
6.5.1 General Points About Interrupts
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An interrupt routine can perform any task performed by any other function,
including accessing global variables, allocating local variables, and calling
other functions.
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When an interrupt routine is entered, the run-time-support function
I$$SAVE is called to save the complete context of the interrupted function.
All
registers are saved. Upon return from the interrupt routine, the run-
time-support function I$$REST is called to restore the environment and
return to the interrupted function.
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The name c_int0 is the C entry point; this name is reserved for the system
reset interrupt. This special interrupt routine initializes the system and
calls the function main. Because it has no caller, c_int0 does not save any
registers.
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To associate an interrupt routine with an interrupt, a branch must be placed
in the appropriate interrupt vector. You can use the assembler and linker
to do this by creating a simple table of branch instructions with the .sect
assembler directive. For information on where the interrupt vector table is
located, consult the user’s guide for the device you are targeting.
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