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61 lines
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61 lines
2.2 KiB
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<TITLE>cc65 function reference: Alphabetical function reference: em_map</TITLE>
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<H2><A NAME="em_map"></A> 3.52 <A HREF="funcref.html#toc3.52">em_map</A></H2>
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<P>
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<BLOCKQUOTE>
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<DL>
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<DT><B>Function</B><DD><P>Make a page of extended memory accessible.</P>
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<DT><B>Header</B><DD><P><CODE>
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<A HREF="funcref-18.html#em.h">em.h</A></CODE></P>
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<DT><B>Declaration</B><DD><P><CODE>void* __fastcall__ em_map (unsigned page);</CODE></P>
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<DT><B>Description</B><DD><P>The function maps one page of extended memory into linear
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memory and returns a pointer to the page frame. Depending on the hardware
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and driver, the data is either mapped into the address space or transfered
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into a buffer. If you don't need the actual contents of the page (for example
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because you're going to overwrite it completely, it is better to call
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<CODE>
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<A HREF="funcref-101.html#em_use">em_use</A></CODE> instead. <CODE>em_use</CODE> will not transfer the
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data if it is possible to avoid that.</P>
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<DT><B>Limits</B><DD><P>
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<UL>
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<LI>Calling <CODE>em_map</CODE> will invalidate the memory window, so if you
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made any changes to the data in the window, call <CODE>
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<A HREF="funcref-92.html#em_commit">em_commit</A></CODE> first, or the changes are lost.</LI>
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<LI>The function is only available as fastcall function, so it may only be
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used in presence of a prototype.</LI>
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<LI>The function produces undefined results if no extended memory driver is
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loaded.</LI>
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</UL>
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</P>
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<DT><B>Availability</B><DD><P>cc65</P>
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<DT><B>See also</B><DD><P>
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<A HREF="funcref-92.html#em_commit">em_commit</A>,
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<A HREF="funcref-96.html#em_load_driver">em_load_driver</A>,
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<A HREF="funcref-101.html#em_use">em_use</A></P>
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<DT><B>Example</B><DD><P>None.</P>
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</DL>
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</P>
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