Understanding Interrupt Subroutines

The ISR address function are declared as "weak" type in startup file.

 In *.s file format  it is like

.word NMI_Handler

and Interrupt address is defined in the line

.weak NMI_Handler                                             //declared as weak type
.thumb_set NMI_Handler,Default_Handler       // NMI_Handler ISR is declared as weak and assigned Default_Handler which is a infinite loop

  In *.c  file format it is like

void WEAK  NMI_Handler(void);

and Interrupt address is defined in the line

#pragma weak NMI_Handler = Default_Handler

whereas
#pragma is for compiler directives that are machine-specific or operating-system-specific, i.e. it tells the compiler to do something, set some option, take some action, override some default, etc. that may or may not apply to all machines and operating systems.


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