ATTENTION! Bootloader upgrade is a risky operation and should not be performed unless absolutely necessary! If anything goes wrong during this process (power shortage, mistype, etc.) the board will be BRICKED (broken). Keep in mind that warranty does not cover Rambutan module if it is damaged due to user's fault.
1. Install tftp server.
2. Copy u-boot binary to the tftp directory.
3. Set 192.168.1.254 IP address on your tftp server's ethernet interface.
4. Reboot Rambutan and press ESC when prompted to enter bootloader then press <Ctrl+C> a few times to clear console buffer.
5. Set local and server IP addresses:
setenv ipaddr 192.168.1.1 setenv serverip 192.168.1.254
6. Download u-boot binary into Rambutan's RAM.
tftpboot 80060000 u-boot.bin
7. Write u-boot binary from RAM to FLASH memory. Warning: do not proceed with this step if step 5 failed !!!
nand erase.part u-boot; nand write 80060000 u-boot ${filesize}
8. Reset board:
reset