How to port pgm_read_byte macro (AVR-GCC) to Mircrochip C18 Compiler?

Question

I'm porting the T6963-based LCD driver from AVR-GCC to the microchip C18 compiler. I have seen the macro "pgm_read_byte": does anyone know how to port this macro?

UPDATE

From here I can see the implementation of the macro

#define   pgm_read_byte(address_short)
pgm_read_byte_near(address_short)
...
#define   pgm_read_byte_near(address_short)   __LPM((uint16_t)(address_short))
...
#define   __LPM(addr)                         __LPM_enhanced__(addr)
...
#define __LPM_enhanced__(addr)  \
(__extension__({                \
    uint16_t __addr16 = (uint16_t)(addr); \
    uint8_t __result;           \
    __asm__                     \
    (                           \
        "lpm %0, Z" "\n\t"      \
        : "=r" (__result)       \
        : "z" (__addr16)        \
    );                          \
    __result;                   \
}))

Answer 1

According to the link you posted, the macro is defined as:

#define   pgm_read_byte(address_short)        pgm_read_byte_near(address_short)
#define   pgm_read_byte_near(address_short)   __LPM((uint16_t)(address_short))

Those macros should be portable without any problems, they're simply aliasing the names of other functions/macros. What specifically are you having trouble with? What have you tried so far, and what went wrong?

Answer 2

AVR is Harvard architecture and pgm_read_ macros serves to access AVR's flash memory which resides in an other address space than RAM.

On a target with a linear address space you can just use the pointers to access the data:

#if defined (__GNUC__) && defined (__AVR__)
#include <avr/pgmspace.h>
#else
#include <stdint.h>
#define PROGMEM /* empty */
#define pgm_read_byte(x) (*(x))
#define pgm_read_word(x) (*(x))
#define pgm_read_float(x) (*(x))
...
#endif