HMS NETWORKS CANbridge NT Lua ADK Bridge Router User Guide

CAN@net NT/CANbridge NT Lua ADK  

Specics in Coding for the Ixxat Lua ADK  

In standard Lua all variables can be classied as globalsor locals. By default, any variable that is referenced  

and not previously declared as localis global. Global variables persist in the global table unl the variable is  

explicitly deleted.  

To see what global variables are in scope, use the following command:  

for k,v in pairs(_G) do print(k,v) end  

Local variables are lexically scoped. This means the scope of local variables is limited to the block where they  

are declared. A block is the body of a control structure, the body of a uncon or a chunk (the le or string  

with the code where the variable is declared). Any variable can be declared localwithin nested blocks or  

uncons without aecng the enclosing scope. Because locals are lexically scoped it is also possible to refer to  

local variables in an outer scope. These variables are sll accessible within the inner scope.  

The Lua runme internally uses hashed key access to retrieve keyed data from a table. Locals are stored as  

a conguous vector and are accessed directly by an index, which is faster. Access to rmware based tables is  

parcularly slow.  

Using locals as follows is both a lot faster at runme and generates less byte code insrucons for their access:  

local can_send = can.send  

2.4.4. Passing Context between Lua Event Tasks  

A single Lua uncon is bound to any event callback task. The uncon is executed from within the relevant  

C code using a lua_call(). Each uncon can invoke other uncons and so on. But each uncon must  

ulmaely return the control to the C library code which then returns the control to the rmware.  

Lua local variables that are dened inside a uncon only exist within the context of this execung Lua uncon.  

Therefore locals are unreferenced on exit and any local data and garbage might be collected between the  

lua_call()acons.  

Context can be passed in two ways between event tasks:  

• by global variables: any global variable persists unl it is explicitly dereferenced by assigning nilto the  

variable.  

• by local variables: local variables that are dened in an outer scope (see descripon of locals in Declaring  

Variables, p. 3).  

Page 4 of 20  

4.02.0332.20002 Version 1.5  

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