Hi Joan,
First of all, thanks for your reply.
Yes, I used android_O8.1.0_1.3.0_8M_tools, I attached my script file and ucl2.xml.
Since our custom board used DDR4, I can't use EVK's uboot image, but I had tried default Image and system.img, the same phenomenon appeared.
I'd tried to move the instruction "find system" to front of "Sending system.img" and it could pass without error; UTP(or uuc!?) always return failed after the instruction "Sending system.img".
I also tried to send a small image(ex. vendor.img) and then all procedure could accomplish.
I thought my USB might be unstable, but the instruction was well received on target board, just a failed result returned.
Best regards,
Oliver