Telnet

Hardware

Telnet is a TCP/IP protocol. It requires a connection to a network (RJ45, twisted pair Ethernet is commonly used). A microcontroller like the Atmega needs a separate module to deal with all the low level stuff. For this recipe an ENC28J60 is used. It is connected via SPI to the Atmega. In addition, the interrupt line of the enc28j60 (pin4) has to be connected to INT2 (pin3 on an Atmega644).

The software needs slightly more that 1KB RAM for itself (mostly buffers), so only the bigger types satisfy this requirement.

Software

The software is currently only available in the Community Repository

Every network needs some settings. As of now, they are hard coded into the code, so you need to change the source code for the MAC address and the IP address in the anc28j60.frt :

\ *** own MAC address ***
$00 constant Mymac1
$22 constant Mymac2
$F9 constant Mymac3
$01 constant Mymac4
$36 constant Mymac5
$B6 constant Mymac6
\ *** own IP address ***
&192 constant Myip1
&168 constant Myip2
&002 constant Myip3
&079 constant Myip4

The code assumes a /24 network for the other network settings.

Using

After uploading the code base (4th_mod1.frt includes most of the dependencies) the serial port is still the command prompt. With the command +telnet the network is started and the TCP Port 23 is opened. In this stage, a network ping should work

serial terminal:
|> +telnet
| ok
|> Send Ping Reply !
|Send Ping Reply !
|Send Ping Reply !
|Send Ping Reply !

remote shell:
|$ ping 192.168.2.79
|PING 192.168.2.79 (192.168.2.79) 56(84) bytes of data.
|64 bytes from 192.168.2.79: icmp_seq=1 ttl=64 time=1037 ms
|64 bytes from 192.168.2.79: icmp_seq=2 ttl=64 time=75.1 ms
|64 bytes from 192.168.2.79: icmp_seq=3 ttl=64 time=19.0 ms
|64 bytes from 192.168.2.79: icmp_seq=4 ttl=64 time=19.0 ms
|64 bytes from 192.168.2.79: icmp_seq=5 ttl=64 time=19.0 ms

To get a telnet session, the amforth command interpreter has to switch its IO

serial terminal:
|> +telnet
| ok
|> +tnredir

remote shell:
$ telnet 192.168.2.79
|Trying 192.168.2.79...
|Connected to 192.168.2.79.
|Escape character is '^]'.
|Start Telnet Server:
| ok
|> 1 2 + .
|1 2 + .
|3  ok
|>
| ok
|> : hi ." Howdy, mate!" cr ;
|: hi ." Howdy, mate!" cr ;
| ok
|>
| ok
|> hi
|hi
|Howdy, mate!
| ok
|>
| ok
|> -tnredir
|-tnredir

serial terminal:
|Stop Telnet Server !  ok
|> hi
|Howdy, mate!
| ok
|>