To upload new firmware you need any TFTP client, for example tftp from the tftp-hpa package on Linux or the built-in TFTP client on Windows.
We recommend connecting the modem directly to the computer, with no other traffic on the network. A remote upgrade is possible, but it is easier when you can see the LCD and, if necessary, reach the serial console.
Connect to the modem and enable TFTP access:
Tahoe> tftp on
Send the empty erase file in binary mode to erase the Flash memory (replace 10.0.0.1 with the modem's IP address):
tftp -m binary 10.0.0.1 -c put erase
After a few seconds the Flash memory is erased.
WARNING: if the modem had firmware version 1.2.8 or older, do not power it off or reboot it until the new firmware is written. In newer versions the bootstrap is never erased and allows firmware recovery after an accidental reboot during the upgrade.
Send the new firmware under the name "flash" (replace the file name with the correct one):
tftp -m binary 10.0.0.1 -c put t680-1.4.2.bin flash
The programming progress is shown on the LCD. If something goes wrong, repeat the procedure: erase the Flash first, then program it again. Finally reboot the modem.