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--- doc:lua:tutorial [2011/06/26 19:26] – admin
+++ doc:lua:tutorial [2014/03/02 07:27] (current) – removed admin
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-====== The OOBD Lua Tutorial ======
-While the page [[start|Lua scripts in OOBD]] tells you the basics about how Lua works inside OOBD, this tutorial will show you how to use Lua to realize your own ideas.
-In this tutorial we'll read the VIN number from a vehicle. While doing that, we'll create a menu, identify the hardware, use the OOBD Lua function library, talk to the vehicle and show the result.
-First we'll need a Menu on the screen to be able to start anything at all. That we'll do with the following code sequence
-<code lua>
-function Start(oldvalue,id)
-	identifyOOBDInterface()
-	openPage("VIN Test")
-	addElement("VIN Number", "vin","-",0x2, "")
-	pageDone()
-	return oldvalue
-end
------------------ Do the initial settings --------------
-Start("","")
-return
-</code>
-So what happens here? When the Lua interpreter runs through the script, it finally finds the
-   Start("","")
-command at the end. This is one of the naming conventions in OOBD: The function, which initializes everything, must be called "Start".
-When we looking into the //Start// function, we'll find
-  identifyOOBDInterface()
-This a function out of the serial_dxm.lua support library. In there you can find several needful functions, which are used by more or less all OOBD scripts, so we've put these functions into a common file.
-//identifyOOBDInterface// evaluates, which OBD hardware dongle is connected to make the further dongle commands inside the library more hardware independent.
-The command sequence //openPage("VIN Test")//, //addElement("VIN Number", "vin","-",0x2, "")// and //pageDone()// create and show a menu, containing the only list entry "VIN Number". The //addElement()// command assigns the lua function //vin// to this menu entry:
-<code lua>
-function vin(oldvalue,id)
-	echoWrite("0902\r")
-	udsLen=receive()
-	if udsLen>0 then
-		if udsBuffer[1]==73 then
-			local pos=4
-			local res=""
-			while pos <= udsLen and pos < 36 do
-				if udsBuffer[pos]>31 then
-					res=res..string.char(udsBuffer[pos])
-				end
-				pos= pos +1
-			end
-			return res
-		else
-			return "Error"
-		end
-	else
-		return "NO DATA"
-	end
-end
-</code>
-This function is called when the user selects the Menu entry "VIN Number". Inside this function first the command
-  echoWrite("0902\r")
-sends the text "0902" as hexadecimal data string to the OBD dongle, which is the OBD standard command to request the vehicle Identification Number (VIN) from a vehicle. The dongle itself forwards this data sequence as binary telegram onto the vehicle diagnostics bus and waits for an answer from the vehicle module.
-The command
-  udsLen=receive()
-picks up the module answer from the OBD dongle. When //udsLen// is greater than 0, it means that something is received. The received bytes themself are stored in the byte array //udsBuffer[]//.
-As we are expect an ASCII VIN number in the received data, we run through the //udsBuffer[]// and join all bytes found as their ASCII values together to the string //res//. This string //res// we than finally return
-  return res
-as the result of this function.
-This is also important to know: All Lua functions which are called from a menu entry must return a string value, as this string is than displayed in the menu as actual value, so it represents the result of the call as feedback to the user.
-And that's already the whole magic... Based on this scheme all wanted functionality can be realized in OOBD with Lua
-  * create a menu entry
-  * link a function to it
-  * do the wanted stuff inside the function
-  * return the result as string