AVR MCU's Expansion of External RAM

I use GCC compiler and C++ to write programs in the project. Theoretically, as long as the external memory is enabled and configured, the address allocation of variables can be completely handed over to the compiler, but the premise is that the memory enable and configuration code must be executed first after power-on reset. When using C or C++ to write programs, the first code to be executed after power-on reset is the startup code and constructor code automatically added by the compiler. I don't know how to make the memory enable and configuration code be executed first after power-on reset, so I wrote the following macro to control the access to the external memory.

code show as below:

//ex te rn_ ram .h

#ifndef _H_EXTERN_RAM_H_

#define _H_EXTERN_RAM_H_

#include "type.h"

#define DEF_EX_VAR(name) EX_VAR name;

#define INIT_EX_VAR(name,ele_size,ele_n) do{

name.size_ele=ele_size;

name.n_ele=ele_n;

name.addr=p;

p+=（（ele_size）*（ele_n））；

}while(0)

#define WR_EX_VAR(name, pos, pdat) do {

for(UINT8 iiiii="0";iiiii(name.addr+(pos)*name.size_ele)［iiiii］=*((INT8 *)pdat+iiiii);

} while (0)

#define RD_EX_VAR(name, pos, pdat) do {

for(UINT8 iiiii="0";iiiii*((INT8 *)pdat+iiiii)=((INT8 *)(name.addr+(pos)*name.size_ele))［iiiii］;

} while (0);

#define GET_P_EX_VAR（name，pos） （name.addr+（pos）*name.size_ele）

typedef struct _tag_ex_var

{

UINT8 size_ele;

UINT16 n_ele;

INT8 *addr;

} EX_VAR;

#endif

Application Examples

//main.cpp

#include "includes.h"

INT8 *p=（INT8*）0x3100; //The address of external RAM starts from 0X3100

DEF_EX_VAR(test); //define an external variable

INT16 main (void)

{

UINT8 i;

INT16 tmp;

INT16 *p_ele;

MCUCR|=0X80; // Enable XRAM and configure it for the fastest access speed

INIT_EX_VAR(test, sizeof(INT16), 100); //External variable initialization, the variable has 100 elements, the element size is sizeof(INT16)

tmp = "0xaaaa";

for (i=0;i<100;i++)

{

WR_EX_VAR (test, i, &tmp); //Write an example to assign the value 0Xaaaa to all elements of the variable test

}

for (i=0;i<100;i++)

{

RD_EX_VAR (test, i, &tmp); //Read example

}

p_ele = (INT16 *)GET_P_EX_VAR (test, 32); //Get the pointer to the 32nd element of the variable test

while(1);

return 0x00;

}