Upgrading firmware using only UART

WARNING !
You can brick your Carambola. There is no way out. Ensure power is rock solid and don't breath while not finished :)

See here for recommended serial port programs and settings for Carambola.

I assume you have latest firmware with UART support. If no, update procedure is described here.
Setup UART connection.
Power on Carambola.
Wait till boot menu appears and press "4"

Please choose the operation:  
  1: Load system code to SDRAM via TFTP.  
  2: Load system code t hen write to Flash via TFTP. 
  3: Boot system code via Flash (default). 
  4: Entr boot command line interface. 
  7: Load Boot Loader code then write to Flash via Serial.  
  9: Load Boot Loader code then write to Flash via TFTP.

To erase the flash type command:

erase 0xbf050000 0xbf7fffff

To transfer binary image to RAM type command:

loadb

To copy uploaded firmware from RAM to FLASH type command:

cp.b 0x80100000 0xbf050000 0x600000

Reboot Carambola after completing these steps. It should boot new firmware firmware.