Serial Communication

wiki

Here's various code and discussions relating to controlling the RS-232 serial communication port from Lua.

Mail List Posts

Using Alien

-- Lua serial communications library.
--
-- Note: currently only works on Win32.
--
-- The implementation uses alien ( http://alien.luaforge.net/ ).
--
-- Warning: not extensively tested.
--
-- Possible improvements:
--   - decide more consistently when to raise or return on error
--     (io.open/fh:read/fh:write return, but Lua
--      Programming Gems, p.137 suggests we perhaps
--      should raise)
--   - add close() method on file handle, possibly
--     via __gc on newproxy() so that it closes upon
--     garbage collection
--
-- D.Manura. 2008-07
-- S.Slobodov, 2009-01: fixed alien interface, fixed a typo,
--    added COM10 and up, made non-blocking
-- D.Manura, 2009-01: add close(); improve exception safety some
-- S.Slobodov, 2009-01: added routines to set DTR and RTS and to query CTS, plus unbuffered transmission
-- Licensed under the same terms as Lua itself (MIT license).
-- Please post patches and improvements.


local M = {}

local alien = require "alien"

-- win32 values for CreateFile
local GENERIC_READ = 0x80000000
local GENERIC_WRITE = 0x40000000
local OPEN_EXISTING = 3

-- win32 parity values
local EVENPARITY = 2
local MARKPARITY = 3
local NOPARITY = 0
local ODDPARITY = 1
local SPACEPARITY = 4

-- win32 stop bit values
local ONESTOPBIT = 0
local ONE5STOPBITS = 1
local TWOSTOPBITS = 2

-- maps parity name to win32 parity value
local parity_to_win32 = {
  even = EVENPARITY,
  mark = MARKPARITY,
  none = NOPARITY,
  odd = ODDPARITY,
  space = SPACEPARITY
}

-- maps stop bits to win32 stop bits value
local stopbits_to_win32 = {
  [1]   = ONESTOPBIT,
  [1.5] = ONE5STOPBITS,
  [2]   = TWOSTOPBITS
}

local kernel32 = alien.load"kernel32.dll"

-- bitwise operators
-- based on http://ricilake.blogspot.com/2007/10/iterating-bits-in-lua.html
-- 1-based indexing
local function bit(p) return 2 ^ (p - 1) end
local function hasbit(x, p) return x % (p + p) >= p end
local function setbit(x, p) return hasbit(x, p) and x or x + p end
local function clearbit(x, p) return hasbit(x, p) and x - p or x end
local function changebit(x, p, b) return b and setbit(x,p) or clearbit(x,p) end


local function get_last_error()
  local FORMAT_MESSAGE_ALLOCATE_BUFFER = 0x00000100
  local FORMAT_MESSAGE_FROM_SYSTEM     = 0x00001000
  local FORMAT_MESSAGE_IGNORE_INSERTS  = 0x00000200

  local LANG_NEUTRAL    = 0x00
  local SUBLANG_DEFAULT = 0x01

  local function MAKELANGID(p, s) return s * 2^10 + p end

  -- C function declarations
  local FormatMessage = assert(kernel32.FormatMessageA)
  FormatMessage:types{ret ='int', abi = 'stdcall', 'int',
      'pointer', 'int', 'int', 'pointer', 'int', 'pointer'}
  local GetLastError = assert(kernel32.GetLastError)
  GetLastError:types{ret = 'int', abi = 'stdcall'}
  local LocalFree = assert(kernel32.LocalFree)
  LocalFree:types{ret = 'pointer', abi = 'stdcall', 'pointer'}

  local buf = alien.buffer(4)
  buf:set(0, buf2, 'pointer')

  local ret = FormatMessage(
    FORMAT_MESSAGE_ALLOCATE_BUFFER + FORMAT_MESSAGE_FROM_SYSTEM
      + FORMAT_MESSAGE_IGNORE_INSERTS,
    nil,
    GetLastError(),
    MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
    buf, -- ref: msg_buf,
    0,
    nil
  )
  if ret == 0 then return "Unknown error." end
  local msg = alien.tostring(buf:get(1,'pointer'))
  LocalFree(buf:get(1, 'pointer'))

  return msg
end


local function config(h, t)
  local speed = t.speed
  local databits = t.databits
  local stopbits = t.stopbits
  local parity = t.parity
  local handshake = t.handshake

  assert(stopbits_to_win32[stopbits])
  assert(parity_to_win32[parity])
  assert(databits == 5 or databits == 6 or databits == 7 or databits == 8)
  assert(type(speed) == 'number' and speed > 0)

  -- C function declarations
  local GetCommState = kernel32.GetCommState
  GetCommState:types{ret = "int", abi = 'stdcall', "pointer", "pointer"}
  local SetCommState = assert(kernel32.SetCommState)
  SetCommState:types{ret = "int", abi = 'stdcall', "pointer", "pointer"}
  local SetCommTimeouts = assert(kernel32.SetCommTimeouts)
  SetCommTimeouts:types{ret = "int", abi = 'stdcall', "pointer", "pointer"}

  local buf = alien.buffer(4*3 + 3*2 + 3*1 + 5*3 + 2*1)
  GetCommState(h, buf)

  local offset_DCBlength = 1
  local offset_BaudRate  = 1 + 1*4
  local offset_flags     = 1 + 2*4
  local offset_XonLim    = 1 + 3*4 + 1*2
  local offset_XoffLim   = 1 + 3*4 + 2*2
  local offset_ByteSize  = 1 + 3*4 + 3*2
  local offset_Parity    = 1 + 3*4 + 3*2 + 1
  local offset_StopBits  = 1 + 3*4 + 3*2 + 2
  local offset_XonChar   = 1 + 3*4 + 3*2 + 3
  local offset_XoffChar  = 1 + 3*4 + 3*2 + 4
  local offset_ErrorChar = 1 + 3*4 + 3*2 + 5
  local offset_EofChar   = 1 + 3*4 + 3*2 + 6
  local offset_EvtChar   = 1 + 3*4 + 3*2 + 7

  buf:set(offset_BaudRate, speed, 'int')

  local bits = buf:get(offset_flags, 'int')
  bits = changebit(bits, bit(1),  true)  -- fBinary
  bits = changebit(bits, bit(2),  parity ~= 'none')  -- fParity
  bits = changebit(bits, bit(3),  handshake == 'hardware') -- fOutxCtsFlow
  bits = changebit(bits, bit(4),  false) -- fOutxDsrFlow (ok?)
  bits = changebit(bits, bit(5),  false) -- fDtrControl[1] (ok?)
  bits = changebit(bits, bit(6),  false) -- fDtrControl[2] (ok?)
  bits = changebit(bits, bit(7),  false) -- fDsrSensitivity (ok?)
  bits = changebit(bits, bit(8),  false) -- fTXContinueOnXoff  (ok?)
  bits = changebit(bits, bit(9),  handshake == 'xon/xoff') -- fOutX
  bits = changebit(bits, bit(10), handshake == 'xon/xoff') -- fInX
  bits = changebit(bits, bit(11), false) -- fErrorChar (ok?)
  bits = changebit(bits, bit(12), false) -- fNull (ok?)
  bits = changebit(bits, bit(13), false) -- fRtsControl [1]
  bits = changebit(bits, bit(14), handshake == 'xon/xoff') -- fRtsControl [2]
  bits = changebit(bits, bit(15), false) -- fAbortOnError (ok?)
  buf:set(offset_flags, bits, 'int')
  buf:set(offset_ByteSize, databits, 'byte')
  buf:set(offset_Parity, parity_to_win32[parity], 'byte')
  buf:set(offset_StopBits, stopbits_to_win32[stopbits], 'byte')

  SetCommState(h, buf)

  -- timeout on receive immediately if no data pending
  --	(so that you have a chance to do bigger an better things)
  -- http://msdn.microsoft.com/en-us/library/aa363437(VS.85).aspx
  local buf = alien.buffer(4*5)      -- _COMMTIMEOUTS:
  buf:set(1, -1, "int")              -- ReadIntervalTimeout
  buf:set(1+4*1, 0, "int")           -- ReadTotalTimeoutMultiplier
  buf:set(1+4*2, 0, "int")           -- ReadTotalTimeoutConstant
  buf:set(1+4*3, 0, "int")           -- WriteTotalTimeoutMultiplier
  buf:set(1+4*4, 0, "int")           -- WriteTotalTimeoutConstant
  SetCommTimeouts(h, buf)
end

local CloseHandle
local function open(t)
  local port = t.port
  assert(type(port) == 'string' and port:match('^COM[0-9]+$'),
    'invalid port name '..port..'; expecting e.g. "COM1"')

  local portNum = port:match("^COM([0-9]+)")
  if portNum+0 >= 10 then port = "\\\\.\\"..port end

  -- C function declarations
  local CreateFile = assert(kernel32.CreateFileA)
  CreateFile:types{ret = "pointer", abi = 'stdcall', "string",
      "int", "int", "pointer", "int", "int", "pointer"}
  CloseHandle = assert(kernel32.CloseHandle)
  CloseHandle:types{ret = 'int', abi = 'stdcall', "pointer"}

  local n = (GENERIC_READ + GENERIC_WRITE) - 2^32 + 1
  local h = CreateFile(port, n, 0, nil, OPEN_EXISTING, 0, nil)

  -- convert handle to int
  local tmp = alien.buffer(4)
  tmp:set(1, h, 'pointer')
  local hnum = tmp:get(1, 'int')
  if hnum == -1 then return nil, get_last_error() end

  local ok, msg = pcall(config, h, t)
  if not ok then
    CloseHandle(h)
    return nil, msg
  end

  return h
end
M.open = open

local function close(h)
  CloseHandle(h)
end
M.close = close

local function send(h, s)
  local WriteFile = assert(kernel32.WriteFile)
  WriteFile:types{ret="int", abi = 'stdcall', "pointer", "string",
      "int", "ref int", "pointer"}

  local bytes_written_buf = alien.buffer(4)

  local ret, nwritten = WriteFile(h, s, #s, 0, nil )
  if ret == 0 or nwritten ~= #s then
    error("failed write: " .. get_last_error())
  end
end
M.send = send

local function receive(h)
  -- C function declarations
  local ReadFile = assert(kernel32.ReadFile)
  ReadFile:types{ ret = 'int', abi = 'stdcall', "pointer",
      "ref char", "int", "ref int", "pointer"}

  local ret, char, nread = ReadFile(h, buffer_buf, 1, 0, nil )
  if ret == 0 then
    error("failed read: " .. get_last_error())
  end
  if char < 0 then char = char+256 end	-- avoid negatives
  return nread == 1 and string.char(char) or nil
end
M.receive = receive

local function receive_all(h)
  local s = ""
  while 1 do
    local c = receive(h)
    if c then
      s = s .. c
    else
      return s
    end
  end
end
M.receive_all = receive_all

local buf = ""
local function async_read_until(h, char)
  while 1 do
    local c = receive(h)
    if c then
      buf = buf .. c
      if c == char then
        local s = buf
        buf = ""
        return s
      end
    else
      return
    end
  end
end

local function SetDTR(h, set)
	local EscapeCommFunction = assert(kernel32.EscapeCommFunction)
	EscapeCommFunction:types{ret="int", abi = 'stdcall', "pointer", "int"}
	if set then
		EscapeCommFunction(h, SETDTR)
	else
		EscapeCommFunction(h, CLRDTR)
	end
end
M.SetDTR = SetDTR

local function SetRTS(h, set)
	local EscapeCommFunction = assert(kernel32.EscapeCommFunction)
	EscapeCommFunction:types{ret="int", abi = 'stdcall', "pointer", "int"}
	if set then
		EscapeCommFunction(h, SETRTS)
	else
		EscapeCommFunction(h, CLRRTS)
	end
end
M.SetRTS = SetRTS

local function GetCTS(h)
	local GetCommModemStatus = assert(kernel32.GetCommModemStatus)
	GetCommModemStatus:types{ret = "int", abi = "stdcall", "pointer", "ref int"}
	local _, CTS = GetCommModemStatus(h, 0)
	return CTS == CTS_ON
end
M.GetCTS = GetCTS

local function TransmitChar(h, c)
	local TransmitCommChar = assert(kernel32.TransmitCommChar)
	TransmitCommChar:types{ret="int", abi = 'stdcall', "pointer", "int"}
	if not TransmitCommChar(h, c) then return nil, get_last_error()
	else return true end
end
M.TransmitChar = TransmitChar

return M

--DavidManura

Using serial

The following is a sample code that redirects all traffic between a serial port and a local socket port. It works for me, but YMMV. Run from Lua command prompt. The outer while loop is to allow repeated reconnects by an ip client without having to restart the script.

local s=require "socket"
local com=require "serial"

if arg[1] == nil then
	print("Usage: "..arg[0].." <socket port> "..
	      "[<com port> [<speed> [<databits> [<parity> [<stopbits>]]]]]")
	print("Example: "..arg[0].." 10000 COM1 38400 8 none 1")
	return
end

local port = tonumber(arg[1]) or 10000
local comport = arg[2] or "COM1"
local speed = tonumber(arg[3]) or 38400
local databits = tonumber(arg[4]) or 8
local parity = arg[5] or "none"
local stopbits = tonumber(arg[6]) or 1

local sp, errmsg = assert(com.open{port=comport, speed=speed,
    databits=databits, stopbits=stopbits, parity=parity})

while true do
	local server = assert(s.bind("127.0.0.1", port ))
	print("waiting for connection on port", port)
	local client = assert(server:accept())
	print("connected")
	client:settimeout(0.1)
	while true do
		local data, errmsg, partial = client:receive()
		if errmsg == "closed" then
			print("connection closed")
			client:close()
			server:close()
			break
		elseif errmsg == "timeout" then data = partial
		elseif errmsg then error(errmsg) end
		if data and data ~= "" then
			for i = 1, #data do
				local c = data:sub(i,i)
				com.send(sp, c)
			end
		end
		data = com.receive_all(sp)
		if data and data ~= "" then
			client:send(data)
		end
	end
end

-- Sergei Slobodov

Using librs232lua

librs232lua[1] is Lua bindings for librs232 library
- librs232 is multiplatform library for serial communications over RS-232 (serial port)
- As of today librs232 supports Windows, Windows CE and Linux
- librs232 is released under MIT license [LGPL, according to the web - Sergei] [Which web? Mail me pls. Thanks - Petr]

No binary packages available yet
Source code is available on github:

: git clone git://github.com/ynezz/librs232.git

You can download TGZ or ZIP archive with sources here:

: http://github.com/ynezz/librs232/downloads

-- Petr �tetiar <ynezz@true.cz>

LuaSys

[LuaSys] contains serial communication functions (portable Windows and non-Windows termious.h).

Others

use serial port like a file -- LuaList:2012-06/msg00494.html (Stellos M)
termios posix API: http://lua-list.2524044.n2.nabble.com/termios-lua-a-binding-to-the-POSIX-APIs-for-terminal-and-serial-devices-td6926830.html
http://luaforge.net/projects/ulserial/

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Last edited June 21, 2012 8:41 am GMT (diff)