I have a code-block, which is written in C for IAR C/C++ Compiler.
__no_init uint8_t u8ramPhysStart_startUp @ 0x20000000;
__no_init uint8_t u8ramPhysEnd_startUp @ 0x2002FFFF;
__no_init uint8_t u8ramTestStart_startUp @ 0x20004008;
__no_init uint8_t u8ramTestEnd_startUp @ 0x20008008;
#define START_ASM (&u8ramPhysStart_startUp)
#define RAMSTART_STRTUP ((uint32_t)START_ASM)
My goal is converting it or rather making it GCC compatible. For this, I rewrite above code like:
unsigned char u8ramPhysStart_startUp __asm("@ 0x20000000");
unsigned char u8ramPhysEnd_startUp __asm("@ 0x2002FFFF");
unsigned char u8ramTestStart_startUp __asm("@ 0x20004008");
unsigned char u8ramTestEnd_startUp __asm("@ 0x20008008");
But after compilation I get following error:
C:\Users\Pc\AppData\Local\Temp\ccyuCWQT.s: Assembler messages:
C:\Users\Pc\AppData\Local\Temp\ccyuCWQT.s:971: Error: expected symbol name
C:\Users\Pc\AppData\Local\Temp\ccyuCWQT.s:972: Error: expected symbol name
Do someone knows, what it means?
I believe the gcc code should be something like
uint8_t __attribute__ ((section(".my_section"))) u8ramPhysStart_startUp;
where .my_section is something you have added to the linker script.
That being said, the only way which you can make allocation at absolute addresses portable, is to stick to pure ISO C:
#define u8ramPhysStart_startUp (*(volatile uint8_t*)0x20000000u)
or in case you want a pointer to an address:
#define u8ramPhysStart_startUp ((volatile uint8_t*)0x20000000u)
The disadvantage of this is that it doesn't actually allocate any memory, but relies on a linker script to handle that part. That's preferable in most cases.
Another disadvantage is that you won't be able to view these "variable" names in a debugger, since they are actually not variables at all. And that's the main reason why some tool chains come up with things like the non-standard @ syntax.