3.23 __ro_placement Keyword

The IAR __ro_placement keyword specifies that the qualified const volatile objects should be placed in read-only memory.

Suggested Replacement

This keyword can be removed when using a memory-placement feature of MPLAB XC8, or alternatively, there are MPLAB XC8 qualifiers that perform a similar task to this keyword.

When enabled (the default state), the MPLAB XC8's const-data-in-program-memory feature places const volatile objects into program memory. In this case, the IAR keyword is redundant and should be removed.

When this feature is disabled, using the -mno-const-data-in-progmem option, use both the const and __memx qualifiers to have these objects placed in program memory.

Caveats

If the const-in-program-memory feature is disabled, alternate versions of the string functions normally provided by <string.h> must be used to access string objects located in program memory.

Examples

Consider migrating IAR code such as:

volatile const int __ro_placement myVar = 2;

volatile int x;
int main(void) {
    x = myVar;
}

to MPLAB XC8 code similar to:

volatile const int myVar = 2;

volatile int x;
int main(void) {
    x = myVar;
}

when building with the const-data-in-program-memory feature enabled.

Further Information

See the Options Specific to AVR Devices section in the MPLAB XC8 C Compiler User's Guide for AVR MCUs for more information on the const-data-in-program-memory feature.