nodemcu-firmware/docs/modules/console.md

Console Module

Since	Origin / Contributor	Maintainer	Source
2024-10-22	jmattsson	jmattsson	console.c

The console modules allows direct access to the system console. The system console has typically been a UART, but by now several options are available across the ESP32 range of SoCs, including UART, USB-Serial-JTAG and USB CDC-ACM.

By default the system console is linked up to provide an interactive Lua shell (REPL — Read-Execute-Print Loop). It also provides a hook for listening in on the data received on the console programatically, and the interactivity may also be disabled (and re-enabled) programatically if so desired.

console.on()

Used to register or deregister a callback function to handle console events.

Syntax

console.on(method, [number/end_char], [function])

Parameters

• method. One of
  • "data" for bytes received on the console
  • "error" if an error condition is encountered on the console
• number/end_char. Only for event data.
  • if pass in a number n, the callback will called when n chars are received.
  • if n=0, will receive every char in buffer.
  • if pass in a one char string "c", the callback will called when "c" is encounterd, or max n=255 received.
• function callback function.
  • event "data" has a callback like this: function(data) end
  • event "error" has a callback like this: function(err) end

To unregister the callback, specify nil as the function.

Returns

nil

Example

-- when 4 chars is received.
console.on("data", 4, function(data)
  print("received from console:", data)
  if data=="quit" then
    console.on("data", 0, nil)
  end
end)
-- when '\r' is received.
console.on("data", "\r", function(data)
  print("received from console:", data)
  if data=="quit\r" then
    console.on("data", 0, nil)
  end
end)

-- error handler
console.on("error", function(err)
  print("error on console:", err)
end)

console.mode()

Controls the interactivity of the console.

Syntax

console.mode(mode)

Parameters

• mode One of
  • console.INTERACTIVE automatically pass console data to the Lua VM for execution. This is the default mode.
  • console.NONINTERACTIVE disables the automatic passing of console data to the Lua VM. The data only goes to the registered "data" callback, if any.

Returns

nil

Example

Implement a REL instead of the usual REPL

console.on("data", "\r", function(line) node.input(line.."\r\n") end)
console.mode(console.NONINTERACTIVE)

Receive potentially binary data on the console, and process it without letting it reach the Lua interpreter.

-- Instantiate a stream handling function that processes a classic framing
-- protocol: <STX><escaped-data><ETX> where <escaped-data> has the
-- STX, ETX and DLE symbols escaped as <DLE><STX>, <DLE><ETX>, <DLE><DLE>.
-- The chunk_cb gets called incrementally with partial stream data which is
-- effectively unescaped. When the end of frame is encountered, the done_cb
-- gets invoked.
function transmission_receiver(chunk_cb, done_cb)
  local inframe = false
  local escaped = false
  local done = false
  local STX = 2
  local ETX = 3
  local DLE = 16
  local function dispatch(data, i, j)
    if (j - i) < 0 then return end
    chunk_cb(data:sub(i, j))
  end
  return function(data)
    if done then return end
    local from
    local to
    for i = 1, #data
    do
      local b = data:byte(i)
      if inframe
      then
        if not from then from = i end -- first valid byte
        if escaped
        then
          escaped = false
        else
          if b == DLE
          then
            escaped = true
            dispatch(data, from, i-1)
            from = nil
          elseif b == ETX
          then
            done = true
            to = i-1
            break
          end
        end
      else -- look for an (unescaped) STX to sync frame start
        if b == DLE then escaped = true
        elseif b == STX and not escaped then inframe = true
        else escaped = false
        end
      end
      -- else ignore byte outside of framing
    end
    if from then dispatch(data, from, to or #data) end
    if done then done_cb() end
  end
end

function print_hex(chunk)
  for i = 1, #chunk
  do
    print(string.format("%02x ", chunk:sub(i,i)))
  end
end

function resume_interactive()
  console.on("data", 0, nil)
  console.mode(console.INTERACTIVE)
end

-- The 0 may be adjusted upwards for improved efficiency, but be mindful to
-- always send enough data to reach the ETX marker.
console.on("data", 0, transmission_receiver(print_hex, resume_interactive))
console.mode(console.NONINTERACTIVE)

Example C program for encoding data suitable for the above.

#include <stdio.h>

#define STX 0x02
#define ETX 0x03
#define DLE 0x10

int main(int argc, char *argv[])
{
  putchar(STX);
  int ch;
  while ((ch = getchar()) != EOF)
  {
    switch(ch)
    {
      case STX: case ETX: case DLE: putchar(DLE); break;
      default: break;
    }
    putchar(ch);
  }
  putchar(ETX);
  return 0;
}

console.write()

Provides ability to write raw, unformatted data to the console.

Syntax

console.write(str_or_num [, str2_or_num ...])

Parameters

• str_or_num Either
  • A string to write to the console. May contain binary data.
  • A number representing the character code to write the console. Multiple parameters may be given, and they will be written in sequence.

Returns

nil

Example

Write "Hello world!\n" to the console, in a roundabout manner

console.write("Hello", 0x20, "world", 0x21, "\n")