Thanks for your response first.
I think you do not understand my question , I mean download image through the TF card ,not online through the mfg.
On other paltform , usually support some tool or document to tell you how to make a tf-boot ,which startup from the tf card first time ,then the bootloader program the image that read from the TF card to the emmc or nandflash . After that ,reboot the system , the OS can startup from the emmc or nandflash. My question is ,how to make such a tf-boot image and how to do ?
Thanks again