关于利用0x68000000作为扩展sram？

stm32f407的板子，外部sram经过测试也是可以用的，测试主要代码如下：
unsigned int data;
void get_data(unsigned int n)
{

data = n;

}

int FSMC_SRAM_ReadBuffer(unsigned char *pBuffer, unsigned int ReadAddr, unsigned int byte)
{

int temp_sum = 0;    
for (int i = 0; i < byte; i++)
{
    data = *(volatile unsigned char *)(Bank1_SRAM3_ADDR + ReadAddr);
    temp_sum += data;
    ReadAddr++;
}
rt_kprintf(" %d\n", temp_sum);
return temp_sum;

}

int FSMC_SRAM_WriteBuffer(unsigned char *pBuffer, unsigned int WriteAddr, unsigned int byte)
{

int sum = 0;
for(int i = 0; i < byte; i++)
{
    get_data(i);
    *(volatile unsigned char *)(Bank1_SRAM3_ADDR + WriteAddr) = data;
    sum += data;
    WriteAddr++;
    while(i == 255)
    {
        i = 0;
        byte = byte - 255;
    }
}
rt_kprintf(" %d\n", sum);
return sum;

}

static void sram_test( unsigned int byte)
{

unsigned int sum = 0;
unsigned int data_sum = 0;
unsigned int temp_sum = 0;

sum = FSMC_SRAM_WriteBuffer(data, 0, byte);
temp_sum = FSMC_SRAM_ReadBuffer(data, 0, byte);

if (sum == temp_sum)
{
    rt_kprintf("read sram success\n");
}
if (sum != temp_sum)
{
    rt_kprintf("read sram failed\n");
}

}
测试结果如下：