向u-boot2010.09添加USB下载功能时，编译出错

/************************
*    common/main.c
*************************/
…………
extern int FriendlyARMGetDataFromUSB (unsigned max_len, unsigned char **data_ptr, unsigned *received_len);
int FriendlyARMGetDataFromUsbAndWriteNand(unsigned max_len, unsigned offset, unsigned MaxNandSize, const char *Name)
{
        int ret;
        unsigned char *RevPtr;
        unsigned RevLen;
        printf("Downloading %s from USB...\n", Name);
        ret = FriendlyARMGetDataFromUSB(max_len, &RevPtr, &RevLen);
        printf("Downloading %s %s\n", Name, ret >= 0 ? "successed" : "failed");
        if (ret < 0) {
                return ret;
        }        
        return ret;
}



/************************
*      cmd_usbd.c
*************************/
…………
int FriendlyARMGetDataFromUSB (unsigned max_len, unsigned char **data_ptr, unsigned *received_len)
{
        /*******实现********/
}

编译u-boot时出错：undefined reference to `FriendlyARMGetDataFromUSB'

哪位大侠能帮忙解答这个问题呢