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<title>MSP430 Function Attributes (Using the GNU Compiler Collection (GCC))</title>
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<a name="MSP430-Function-Attributes"></a>
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<div class="header">
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<p>
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Next: <a href="NDS32-Function-Attributes.html#NDS32-Function-Attributes" accesskey="n" rel="next">NDS32 Function Attributes</a>, Previous: <a href="MIPS-Function-Attributes.html#MIPS-Function-Attributes" accesskey="p" rel="prev">MIPS Function Attributes</a>, Up: <a href="Function-Attributes.html#Function-Attributes" accesskey="u" rel="up">Function Attributes</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="MSP430-Function-Attributes-1"></a>
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<h4 class="subsection">6.31.19 MSP430 Function Attributes</h4>
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<p>These function attributes are supported by the MSP430 back end:
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</p>
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<dl compact="compact">
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<dt><code>critical</code></dt>
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<dd><a name="index-critical-function-attribute_002c-MSP430"></a>
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<p>Critical functions disable interrupts upon entry and restore the
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previous interrupt state upon exit. Critical functions cannot also
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have the <code>naked</code> or <code>reentrant</code> attributes. They can have
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the <code>interrupt</code> attribute.
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</p>
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</dd>
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<dt><code>interrupt</code></dt>
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<dd><a name="index-interrupt-function-attribute_002c-MSP430"></a>
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<p>Use this attribute to indicate
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that the specified function is an interrupt handler. The compiler generates
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function entry and exit sequences suitable for use in an interrupt handler
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when this attribute is present.
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</p>
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<p>You can provide an argument to the interrupt
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attribute which specifies a name or number. If the argument is a
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number it indicates the slot in the interrupt vector table (0 - 31) to
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which this handler should be assigned. If the argument is a name it
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is treated as a symbolic name for the vector slot. These names should
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match up with appropriate entries in the linker script. By default
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the names <code>watchdog</code> for vector 26, <code>nmi</code> for vector 30 and
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<code>reset</code> for vector 31 are recognized.
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</p>
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</dd>
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<dt><code>naked</code></dt>
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<dd><a name="index-naked-function-attribute_002c-MSP430"></a>
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<p>This attribute allows the compiler to construct the
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requisite function declaration, while allowing the body of the
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function to be assembly code. The specified function will not have
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prologue/epilogue sequences generated by the compiler. Only basic
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<code>asm</code> statements can safely be included in naked functions
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(see <a href="Basic-Asm.html#Basic-Asm">Basic Asm</a>). While using extended <code>asm</code> or a mixture of
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basic <code>asm</code> and C code may appear to work, they cannot be
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depended upon to work reliably and are not supported.
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</p>
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</dd>
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<dt><code>reentrant</code></dt>
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<dd><a name="index-reentrant-function-attribute_002c-MSP430"></a>
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<p>Reentrant functions disable interrupts upon entry and enable them
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upon exit. Reentrant functions cannot also have the <code>naked</code>
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or <code>critical</code> attributes. They can have the <code>interrupt</code>
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attribute.
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</p>
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</dd>
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<dt><code>wakeup</code></dt>
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<dd><a name="index-wakeup-function-attribute_002c-MSP430"></a>
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<p>This attribute only applies to interrupt functions. It is silently
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ignored if applied to a non-interrupt function. A wakeup interrupt
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function will rouse the processor from any low-power state that it
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might be in when the function exits.
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</p>
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</dd>
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<dt><code>lower</code></dt>
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<dt><code>upper</code></dt>
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<dt><code>either</code></dt>
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<dd><a name="index-lower-function-attribute_002c-MSP430"></a>
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<a name="index-upper-function-attribute_002c-MSP430"></a>
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<a name="index-either-function-attribute_002c-MSP430"></a>
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<p>On the MSP430 target these attributes can be used to specify whether
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the function or variable should be placed into low memory, high
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memory, or the placement should be left to the linker to decide. The
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attributes are only significant if compiling for the MSP430X
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architecture.
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</p>
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<p>The attributes work in conjunction with a linker script that has been
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augmented to specify where to place sections with a <code>.lower</code> and
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a <code>.upper</code> prefix. So, for example, as well as placing the
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<code>.data</code> section, the script also specifies the placement of a
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<code>.lower.data</code> and a <code>.upper.data</code> section. The intention
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is that <code>lower</code> sections are placed into a small but easier to
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access memory region and the upper sections are placed into a larger, but
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slower to access, region.
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</p>
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<p>The <code>either</code> attribute is special. It tells the linker to place
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the object into the corresponding <code>lower</code> section if there is
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room for it. If there is insufficient room then the object is placed
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into the corresponding <code>upper</code> section instead. Note that the
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placement algorithm is not very sophisticated. It does not attempt to
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find an optimal packing of the <code>lower</code> sections. It just makes
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one pass over the objects and does the best that it can. Using the
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<samp>-ffunction-sections</samp> and <samp>-fdata-sections</samp> command-line
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options can help the packing, however, since they produce smaller,
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easier to pack regions.
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</p></dd>
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</dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="NDS32-Function-Attributes.html#NDS32-Function-Attributes" accesskey="n" rel="next">NDS32 Function Attributes</a>, Previous: <a href="MIPS-Function-Attributes.html#MIPS-Function-Attributes" accesskey="p" rel="prev">MIPS Function Attributes</a>, Up: <a href="Function-Attributes.html#Function-Attributes" accesskey="u" rel="up">Function Attributes</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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