Giant.Metal.Robot

The example net example in the nodemcu docs works ok talking to a busybox telnetd, but when trying to talk to an old Linux NetKit (0.17) in.telnetd running on a bifferboard it chokes on the telnet option negotiation.
The man page for the sever does say
"Because of bugs in the original 4.2 BSD telnet(1), telnetd performs some dubious protocol exchanges"

So, wading thru RFCs and wireshark captures to fake up the telnet options results in this :

-- tn.lua =====================================



-- TELNET OPTIONS
NUL = string.char(0)
ECHO = string.char(1)
SGA = string.char(3)
ESC = string.char(27)
FLOWCONTROL = string.char(33)
SUB = string.char(250)
WILL = string.char(251)   --fb
WONT = string.char(252)   --fc
DO = string.char(253)     --fd 
DONT = string.char(254)   --fe 
IAC = string.char(255)    --ff
AYT = string.char(246)  -- ARE YOU THERE
SE = string.char(240)  -- End of subnegotiation
GA = string.char(249) -- GO AHEAD
BRK = string.char(243)  -- BRK
IP = string.char(244) -- INTERUPT PROCESS
DM = string.char(244)  -- DATA MARK

optionsSent = nil  
buffer = ""
hexprint = function(s) 
 for z=1,#s  do 
    uart.write(0, string.format("/x%x - %d ",string.byte(s,z),string.byte(s,z)))
 end
end

function conff = function(s,...)  return s:format(...) end

telnetOptions =  IAC .. DO .. SGA .. 
                 IAC .. WILL .. string.char(24).. 
                 IAC .. WILL .. string.char(31) ..
                 IAC .. WILL .. string.char(32) .. 
                 IAC .. WONT .. FLOWCONTROL .. 
                 IAC .. WILL .. string.char(34) ..
                 IAC .. WILL .. string.char(39) .. 
                 IAC .. DO .. string.char(05) .. 
                 IAC .. WILL .. string.char(35)
    
--subptions 
telnetSubOptions = IAC .. SUB .. string.char(31) .. NUL .. string.char(80) .. NUL .. string.char(24) .. IAC .. SE ..
IAC .. SUB .. string.char(32) .. NUL .. "115200,115200" .. IAC .. SE  ..
IAC .. SUB .. string.char(35) .. NUL .. "ESP8266" .. IAC .. SE ..  
IAC .. SUB .. string.char(39) .. NUL .. "ESP8266" .. IAC .. SE .. 
IAC .. SUB .. string.char(24) .. NUL .. "ansi" .. IAC .. SE
       
if IP and LOGIN and PASSWORD then 
conn=net.createConnection(net.TCP, false)

conn:on("connection", function(sck, c)
 if DEBUG then print ("*** Connection ***")  end
 optionsSent = 1 
 conn:send(telnetOptions)
 if DEBUG then print "** Telnet options SENT ***"  end 
end )

conn:on("sent",function(sck,c) 
 -- print "**** SENT ***" 
 if optionsSent == 1 then
   if DEBUG then print "** Telnet sub options SENT ***" end 
   conn:send(telnetSubOptions)
   optionsSent = optionsSent + 1 
   end
 end )

conn:on("receive", function(sck, c) 
 if DEBUG then print ("*** Receiving ***") end

 if string.find(c, IAC .. DO .. string.char(24)) then 
  print("DO TERMINAL") 
-- conn:send(conff("%c%c%c",IAC,DO,24))
 end

 if string.find(c, IAC .. DO .. string.char(32)) then 
  print("DO TSPEED") 
-- conn:send(conff("%c%c%c",IAC,DO,32))
 end

 if string.find(c, IAC .. DO .. string.char(35)) then
   print("DO XDISPLOC") 
-- conn:send(conff("%c%c%c",IAC,DO,32))
 end

 if string.find(c, IAC .. DO .. string.char(39)) then 
  print("DO ENVIRON") 
-- conn:send(conff("%c%c%c",IAC,DO,39))
-- conn:send(conff("%c%c%c",IAC,DO,03))
 end

  if string.find(c, IAC .. DO .. ECHO ) then  
   conn:send(IAC .. WONT .. ECHO) -- WONT DO ECHO 
   print "rec do echo, send wont"
 end

  if string.find(c, IAC .. WILL .. ECHO ) then 
  conn:send(IAC .. DO .. ECHO) -- WONT DO ECHO 
  print "rec will echo, sending do"
 end

  if string.find(c, IAC .. SUB .. FLOWCONTROL .. NUL ) then  
    print ("REMOTE FLOW CONTROL OFF")
 end

  if string.find(c, IAC .. SUB .. FLOWCONTROL .. string.char(01) ) then  
    print ("REMOTE FLOW CONTROL ON")
    tmr.delay(100) 
 end

 if  string.find(c, "gin:") then conn:send(LOGIN .. "\n") end

 if string.find(c, "word:") then conn:send(PASSWORD .. "\n") end

  uart.write(0,c) 

end )

 uart.on("data", 0 ,
   function(data)
    if buffer == "" then 
      buffer = data
    else 
      buffer = buffer .. data 
    end


     if string.find(buffer,"+++q")  then
       uart.on("data") -- unregister callback function
       conn:close()
     end
     
     if string.find(buffer,"+++c") then
        buffer = ""
        conn:connect(23,HOSTIP)
     end
     
    if #buffer > 20 then buffer = "" end 
    if string.find(buffer,"\r")  then buffer = "" end 
  
       
   if string.find(buffer,ESC ) then 
     if DEBUG then hexprint ( buffer  ) end 
     if string.find(buffer,ESC .. ESC ) then 
       conn:send( ESC )
       buffer = "" 
     end           

    -- CURSOR KEYS 
    CURSORKEY =  ESC .. "%[%u"
      if string.find(buffer,CURSORKEY ) then 
        if DEBUG then hexprint ( buffer  ) end 
        conn:send( string.match(buffer,CURSORKEY ))
        buffer = "" 
      end           
   
    else
        conn:send( data )
    end 
 end, 0) 

 print "+++c to connect , +++q to disconnect"

 else 
 print ("define HOSTIP, LOGIN and PASSWORD and try again")
 end 

--=======================================================

this works for the old server, but doesn't work on a busybox telnetd or a newer telnetd (GNU inetutils) 1.9.2. it needs a proper state machine to do negotiation.

And you need to push escape twice to send escape, it is a work in progress.

Finally received M5's latest tiny ESP32 module (it was way delayed due to the virus). Tried some demos, the LedDisplay demo doesn't work unless you change as per this advice:

"change in LED_DisPlay.ccp line 103
// xSemaphoreTake(_xSemaphore, portMAX_DELAY);
xSemaphoreTake(_xSemaphore, 100);"

from ririfonfon on the M5Stack/M5Atom forum.

And then, a binary clock based on SimpleTime from the ESP32 examples, gets the time from NTP and displays on the M5Atom's leds.

The M5Atom set up uses the FastLed library but for some reason the colours work strange if you use the defined colour constants eg, if you use "CRGB::Red" the led lights green and vice-versa .

The fifth column is the seconds/2 in binary. The hours and minutes are BCD.

It does need a daylight savings check added.

the code is here