3.21 __raw Keyword

The IAR __raw keyword prevents saving call-used registers in interrupt functions.

Suggested Replacement

There is no MPLAB XC8 feature that performs the same function as this keyword; however, there is an attribute which performs a similar task.

The naked attribute can be used to prevent generation of the entire prologue and epilogue context switching associated with an interrupt function.

Caveats

The naked attribute prevents the call-used registers from being saved, but it also omits code that performs other operations typically required by interrupt functions, such as generation of the reti instruction, and saving and clearing r1 (__zero_reg__) on entry, and the reverse process on exit.

Examples

Consider migrating IAR code such as:

volatile int x;
 
#pragma vector=2
__raw __interrupt void incIsr(void) {
    x++;
}

to MPLAB XC8 code similar to:

#include <xc.h>
 
volatile int x;
void __attribute__((naked)) __interrupt(2) incIsr(void) {
    // insert hand-written context switch code here
    x++;
    // insert hand-written context switch and return-from-interrupt code here
}

Further Information

See the Interrupts section in the MPLAB XC8 C Compiler User's Guide for AVR MCUs for more information on writing interrupt functions.