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<H2><A NAME="SECTION000416000000000000000">
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3.16 MCS51 Memory Models</A>
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<P>
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SDCC allows two memory models for MCS51 code, small and large. Modules
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compiled with different memory models should <I>never</I> be combined
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together or the results would be unpredictable. The library routines
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supplied with the compiler are compiled as both small and large. The
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compiled library modules are contained in seperate directories as
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small and large so that you can link to either set.
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<P>
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When the large model is used all variables declared without a storage
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class will be allocated into the external ram, this includes all parameters
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and local variables (for non-reentrant functions). When the small
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model is used variables without storage class are allocated in the
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internal ram.
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<P>
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Judicious usage of the processor specific storage classes and the
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'reentrant' function type will yield much more efficient code, than
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using the large model. Several optimizations are disabled when the
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program is compiled using the large model, it is therefore strongly
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recommdended that the small model be used unless absolutely required.
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HREF="node19.html">3. Using SDCC</A>
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<ADDRESS>
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<I>Johan Knol</I>
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<BR><I>2001-07-13</I>
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