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— | doc:lua_tutorial [2014/03/02 07:26] (current) – created admin | ||
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+ | ====== The OOBD Lua Tutorial ====== | ||
+ | While the page [[doc: | ||
+ | |||
+ | 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, | ||
+ | identifyOOBDInterface() | ||
+ | openPage(" | ||
+ | addElement(" | ||
+ | pageDone() | ||
+ | return oldvalue | ||
+ | end | ||
+ | |||
+ | |||
+ | ----------------- Do the initial settings -------------- | ||
+ | |||
+ | Start("","" | ||
+ | return | ||
+ | </ | ||
+ | |||
+ | So what happens here? When the Lua interpreter runs through the script, it finally finds the | ||
+ | |||
+ | | ||
+ | |||
+ | command at the end. This is one of the naming conventions in OOBD: The function, which initializes everything, must be called " | ||
+ | |||
+ | 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. | ||
+ | |||
+ | // | ||
+ | |||
+ | |||
+ | The command sequence // | ||
+ | |||
+ | |||
+ | <code lua> | ||
+ | function vin(oldvalue, | ||
+ | echoWrite(" | ||
+ | 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]> | ||
+ | res=res..string.char(udsBuffer[pos]) | ||
+ | end | ||
+ | pos= pos +1 | ||
+ | end | ||
+ | return res | ||
+ | else | ||
+ | return " | ||
+ | end | ||
+ | else | ||
+ | return "NO DATA" | ||
+ | end | ||
+ | end | ||
+ | </ | ||
+ | |||
+ | This function is called when the user selects the Menu entry "VIN Number" | ||
+ | |||
+ | echoWrite(" | ||
+ | |||
+ | sends the text " | ||
+ | |||
+ | 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 // | ||
+ | |||
+ | As we are expect an ASCII VIN number in the received data, we run through the // | ||
+ | |||
+ | 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 | ||
+ | |
doc/lua_tutorial.txt · Last modified: 2014/03/02 07:26 by admin