Rambutan's bootloader (Caraboot) includes a USB boot capability (starting from version 2.0) which supports reading files from USB storage (formatted in FAT32) and using them to boot a Linux image or write to internal flash memory.

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1. Format your USB drive as FAT32 and copy the firmware. Make sure to rename your rambutan-initramfs-kernel.bin image to 8dev_uimage.bin, otherwise the board will not detect your firmware.

2. Plug the USB drive into Rambutan's USB port.

3. Keep holding the S1 (reset-to-defaults) button and slightly press S2 (hardware-reset) button, the bootloader will begin to search your USB drive for firmware. Wait for about 10 seconds and release the S1 button. The board will continue booting from USB.

Since the firmware is running Live of a USB drive any configuration changes made will be cleared once your device is rebooted.
This is a useful method to check whether firmware runs smoothly before making the final decision to flash to internal memory.