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+
+<H2><A NAME="SECTION00045000000000000000">
+3.5 Parameters & Local Variables</A>
+</H2>
+
+<P>
+Automatic (local) variables and parameters to functions can either
+be placed on the stack or in data-space. The default action of the
+compiler is to place these variables in the internal RAM (for small
+model) or external RAM (for Large model). This in fact makes them
+<I>static</I> so by default functions are non-reentrant.
+
+<P>
+They can be placed on the stack either by using the <I>-stack-auto</I>
+compiler option or by using the <I>reentrant</I> keyword in the function
+declaration, e.g.:
+<BR>
+
+<BR>
+<TT>unsigned char foo(char i) reentrant </TT>
+<BR>
+<TT>{ </TT>
+<BR>
+<TT>... </TT>
+<BR>
+<TT>}</TT>
+<BR>
+
+<BR>
+Since stack space on 8051 is limited, the <I>reentrant</I> keyword
+or the <I>-stack-auto</I> option should be used sparingly. Note that
+the reentrant keyword just means that the parameters & local variables
+will be allocated to the stack, it <I>does not</I> mean that the function
+is register bank independent.
+<BR>
+
+<BR>
+Local variables can be assigned storage classes and absolute addresses,
+e.g.:
+<BR>
+
+<BR>
+<TT>unsigned char foo() {</TT>
+<BR>
+<TT> xdata unsigned char i;</TT>
+<BR>
+<TT> bit bvar;</TT>
+<BR>
+<TT> data at 0x31 unsiged char j;</TT>
+<BR>
+<TT> ... </TT>
+<BR>
+<TT>}</TT>
+<BR>
+<BR>
+In the above example the variable <I>i</I> will be allocated in the
+external ram, <I>bvar</I> in bit addressable space and <I>j</I> in
+internal ram. When compiled with <I>-stack-auto</I> or when a function
+is declared as <I>reentrant</I> this can only be done for static variables.
+
+<P>
+Parameters however are not allowed any storage class, (storage classes
+for parameters will be ignored), their allocation is governed by the
+memory model in use, and the reentrancy options.
+
+<P>
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+<ADDRESS>
+<I>Johan Knol</I>
+<BR><I>2001-07-13</I>
+</ADDRESS>
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