关于把全局变量从ROM区拷贝到RAM的问题（已解决）

无悔的湖光

我们都知道，全局变量是烧在ROM区的，在芯片启动以后，全局变量是手动从ROM区拷贝到RAM区的，既然全局变量是可以修改值得，那么我们在程序中用到的全局变量应该是拷贝到RAM区中的全局变量，但是烧写的时候是烧在ROM中的，那么程序是怎么定位到RAM区中的（从ROM到RAM的拷贝手动的，程序应该从源地址ROM中取值，而不是RAM中）？

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安

变量只能定义在RAM中，常量可以定义在ROM中，因为ROM中的数据不能改动，除非你用FLASH的擦写命令来进行修改。

FSL_TICS_MAHUI

 不知道你用的是什么编译工具？CodeWarrior还是IAR?飞思卡尔例程中提供了数据从ROM拷贝到RAM的代码。
 
 
/********************************************************************/
void
common_startup(void)
{
 
#if (defined(CW))
    extern char __START_BSS[];
    extern char __END_BSS[];
    extern uint32 __DATA_ROM[];
    extern uint32 __DATA_RAM[];
    extern char __DATA_END[];
#endif
 
    /* Declare a counter we'll use in all of the copy loops */
    uint32 n;
 
    /* Declare pointers for various data sections. These pointers
     * are initialized using values pulled in from the linker file
     */
    uint8 * data_ram, * data_rom, * data_rom_end;
    uint8 * bss_start, * bss_end;
 
 
    /* Addresses for VECTOR_TABLE and VECTOR_RAM come from the linker file */
    extern uint32 __VECTOR_TABLE[];
    extern uint32 __VECTOR_RAM[];
 
    /* Copy the vector table to RAM */
    if (__VECTOR_RAM != __VECTOR_TABLE)
    {
        for (n = 0; n < 0x410; n++)
            __VECTOR_RAM[n] = __VECTOR_TABLE[n];
    }
    /* Point the VTOR to the new copy of the vector table */
    write_vtor((uint32)__VECTOR_RAM);
 
    /* Get the addresses for the .data section (initialized data section) */
#if (defined(CW))
        data_ram = (uint8 *)__DATA_RAM;
   data_rom = (uint8 *)__DATA_ROM;
   data_rom_end  = (uint8 *)__DATA_END; /* This is actually a RAM address in CodeWarrior */
   n = data_rom_end - data_ram;
    #elif (defined(IAR))
data_ram = __section_begin(".data");
data_rom = __section_begin(".data_init");
data_rom_end = __section_end(".data_init");
n = data_rom_end - data_rom;
#endif
 
/* Copy initialized data from ROM to RAM */
while (n--)
*data_ram++ = *data_rom++;
 
 
    /* Get the addresses for the .bss section (zero-initialized data) */
#if (defined(CW))
bss_start = (uint8 *)__START_BSS;
bss_end = (uint8 *)__END_BSS;
#elif (defined(IAR))
bss_start = __section_begin(".bss");
bss_end = __section_end(".bss");
#endif
 
 
 
 
    /* Clear the zero-initialized data section */
    n = bss_end - bss_start;
    while(n--)
      *bss_start++ = 0;
 
/* Get addresses for any code sections that need to be copied from ROM to RAM.
* The IAR tools have a predefined keyword that can be used to mark individual
* functions for execution from RAM. Add "__ramfunc" before the return type in
* the function prototype for any routines you need to execute from RAM instead
* of ROM. ex: __ramfunc void foo(void);
*/
#if (defined(IAR))
uint8* code_relocate_ram = __section_begin("CodeRelocateRam");
uint8* code_relocate = __section_begin("CodeRelocate");
uint8* code_relocate_end = __section_end("CodeRelocate");
 
/* Copy functions from ROM to RAM */
n = code_relocate_end - code_relocate;
while (n--)
*code_relocate_ram++ = *code_relocate++;
#endif
}