Enabling and configuring the TFTP daemon is detailed in SUG Section 6.3-Services TFTP.

On XigmaNAS, you can test whether the TFTP server is running with the netstat command. If it isn't running there will be no response:

xigmanas:~# netstat -a | grep tftp
xigmanas:~#

If it is running you will see something like the following:

xigmanas:~# netstat -a | grep tftp
udp6 0 0 *.tftp *.*
udp4 0 0 *.tftp *.*
xigmanas:~#

If you want to connect to your server remotely from a client, you can try these commands:

you@windowspc:~$ tftp Your_XigmaNAS_IP_Address
tftp> status
Connected to Your_XigmaNAS_IP_Address .
Mode: netascii Verbose: off Tracing: off
Rexmt-interval: 5 seconds, Max-timeout: 25 seconds
tftp> quit
you@windowspc:~$

Ref: TFTP Client Man page.