24.4.3 Far Objects and Functions

The __far qualifier can be used to indicate that variables or functions are located in ‘far memory’. Exactly what constitutes far memory is dependent on the target device, but it is typically memory that requires more complex code to access. Expressions involving far-qualified objects usually generate slower and larger code.

Use the native keywords discussed in the Differences section to look up information on the semantics of this qualifier.

Some devices may not have such memory implemented, in which case, use of this qualifier is ignored. Stack-based (auto and parameter) variables cannot use the __far specifier.

Example

The following shows a variable and function qualified using __far.

__far int serialNo;

__far int ext_getCond(int selector);

Differences

When targeting PIC devices, the MPLAB XC8 compiler has allowed the far specifier to be used with variables. This specifier has not been allowed with functions. When targeting AVR devices, MPLAB XC8 has not implemented any “far” memory.

The MPLAB XC16 and XC-DSC compilers have used the far attribute with both variables and functions.

The MPLAB XC32 compiler has used the far attribute with functions only.

Migration to the CCI

When targeting PIC devices with the MPLAB XC8 compiler, change any occurrence of the far qualifier to __far, for example, from:

far char template[20];

to:

__far char template[20];

When using MPLAB XC16, XC-DSC or XC32 compilers, change any occurrence of the far attribute to the __far specifier, for example, from:

void bar(void) __attribute__ ((far));

int tblIdx __attribute__ ((far));

to:

void __far bar(void);