135 lines
5 KiB
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135 lines
5 KiB
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<B> Next:</B> <A NAME="tex2html683"
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HREF="node30.html">3.11 Absolute Addressing</A>
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<B> Up:</B> <A NAME="tex2html677"
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HREF="node19.html">3. Using SDCC</A>
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<B> Previous:</B> <A NAME="tex2html671"
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HREF="node28.html">3.9 Naked Functions</A>
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  <B> <A NAME="tex2html679"
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HREF="node1.html">Contents</A></B>
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  <B> <A NAME="tex2html681"
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HREF="node61.html">Index</A></B>
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<H2><A NAME="SECTION000410000000000000000">
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3.10 Functions using private banks</A>
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</H2>
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<P>
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The <I>using</I> attribute (which tells the compiler to use a register
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bank other than the default bank zero) should only be applied to <I>interrupt</I>
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functions (see note 1 below). This will in most circumstances make
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the generated ISR code more efficient since it will not have to save
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registers on the stack.
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<P>
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The <I>using</I> attribute will have no effect on the generated code
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for a <I>non-interrupt</I> function (but may occasionally be useful
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anyway<A NAME="tex2html1"
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HREF="footnode.html#foot531"><SUP>1</SUP></A>).
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<BR>
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<I>(pending: I don't think this has been done yet)</I>
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<P>
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An <I>interrupt</I> function using a non-zero bank will assume that
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it can trash that register bank, and will not save it. Since high-priority
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interrupts can interrupt low-priority ones on the 8051 and friends,
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this means that if a high-priority ISR <I>using</I> a particular bank
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occurs while processing a low-priority ISR <I>using</I> the same bank,
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terrible and bad things can happen. To prevent this, no single register
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bank should be <I>used</I> by both a high priority and a low priority
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ISR. This is probably most easily done by having all high priority
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ISRs use one bank and all low priority ISRs use another. If you have
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an ISR which can change priority at runtime, you're on your own: I
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suggest using the default bank zero and taking the small performance
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hit.
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<P>
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It is most efficient if your ISR calls no other functions. If your
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ISR must call other functions, it is most efficient if those functions
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use the same bank as the ISR (see note 1 below); the next best is
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if the called functions use bank zero. It is very inefficient to call
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a function using a different, non-zero bank from an ISR.
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<BR>
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<B> Next:</B> <A NAME="tex2html683"
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HREF="node30.html">3.11 Absolute Addressing</A>
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<B> Up:</B> <A NAME="tex2html677"
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HREF="node19.html">3. Using SDCC</A>
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<B> Previous:</B> <A NAME="tex2html671"
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HREF="node28.html">3.9 Naked Functions</A>
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  <B> <A NAME="tex2html679"
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HREF="node1.html">Contents</A></B>
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  <B> <A NAME="tex2html681"
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HREF="node61.html">Index</A></B>
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<!--End of Navigation Panel-->
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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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</ADDRESS>
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