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diff --git a/share/doc/gcc/AVR-Function-Attributes.html b/share/doc/gcc/AVR-Function-Attributes.html new file mode 100644 index 0000000..20b985c --- /dev/null +++ b/share/doc/gcc/AVR-Function-Attributes.html @@ -0,0 +1,199 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- This file documents the use of the GNU compilers. + +Copyright (C) 1988-2023 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being "Funding Free Software", the Front-Cover +Texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). 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The compiler generates +function entry and exit sequences suitable for use in an interrupt handler +when this attribute is present. +</p> +<p>On the AVR, the hardware globally disables interrupts when an +interrupt is executed. The first instruction of an interrupt handler +declared with this attribute is a <code>SEI</code> instruction to +re-enable interrupts. See also the <code>signal</code> function attribute +that does not insert a <code>SEI</code> instruction. If both <code>signal</code> and +<code>interrupt</code> are specified for the same function, <code>signal</code> +is silently ignored. +</p> +<a name="index-naked-function-attribute_002c-AVR"></a> +</dd> +<dt><code>naked</code></dt> +<dd><p>This attribute allows the compiler to construct the +requisite function declaration, while allowing the body of the +function to be assembly code. The specified function will not have +prologue/epilogue sequences generated by the compiler. Only basic +<code>asm</code> statements can safely be included in naked functions +(see <a href="Basic-Asm.html#Basic-Asm">Basic Asm</a>). While using extended <code>asm</code> or a mixture of +basic <code>asm</code> and C code may appear to work, they cannot be +depended upon to work reliably and are not supported. +</p> +<a name="index-no_005fgccisr-function-attribute_002c-AVR"></a> +</dd> +<dt><code>no_gccisr</code></dt> +<dd><p>Do not use <code>__gcc_isr</code> pseudo instructions in a function with +the <code>interrupt</code> or <code>signal</code> attribute aka. interrupt +service routine (ISR). +Use this attribute if the preamble of the ISR prologue should always read +</p><div class="example"> +<pre class="example">push __zero_reg__ +push __tmp_reg__ +in __tmp_reg__, __SREG__ +push __tmp_reg__ +clr __zero_reg__ +</pre></div> +<p>and accordingly for the postamble of the epilogue — no matter whether +the mentioned registers are actually used in the ISR or not. +Situations where you might want to use this attribute include: +</p><ul> +<li> Code that (effectively) clobbers bits of <code>SREG</code> other than the +<code>I</code>-flag by writing to the memory location of <code>SREG</code>. +</li><li> Code that uses inline assembler to jump to a different function which +expects (parts of) the prologue code as outlined above to be present. +</li></ul> +<p>To disable <code>__gcc_isr</code> generation for the whole compilation unit, +there is option <samp>-mno-gas-isr-prologues</samp>, see <a href="AVR-Options.html#AVR-Options">AVR Options</a>. +</p> +<a name="index-OS_005fmain-function-attribute_002c-AVR"></a> +<a name="index-OS_005ftask-function-attribute_002c-AVR"></a> +</dd> +<dt><code>OS_main</code></dt> +<dt><code>OS_task</code></dt> +<dd><p>On AVR, functions with the <code>OS_main</code> or <code>OS_task</code> attribute +do not save/restore any call-saved register in their prologue/epilogue. +</p> +<p>The <code>OS_main</code> attribute can be used when there <em>is +guarantee</em> that interrupts are disabled at the time when the function +is entered. This saves resources when the stack pointer has to be +changed to set up a frame for local variables. +</p> +<p>The <code>OS_task</code> attribute can be used when there is <em>no +guarantee</em> that interrupts are disabled at that time when the function +is entered like for, e.g. task functions in a multi-threading operating +system. In that case, changing the stack pointer register is +guarded by save/clear/restore of the global interrupt enable flag. +</p> +<p>The differences to the <code>naked</code> function attribute are: +</p><ul> +<li> <code>naked</code> functions do not have a return instruction whereas +<code>OS_main</code> and <code>OS_task</code> functions have a <code>RET</code> or +<code>RETI</code> return instruction. +</li><li> <code>naked</code> functions do not set up a frame for local variables +or a frame pointer whereas <code>OS_main</code> and <code>OS_task</code> do this +as needed. +</li></ul> + +<a name="index-signal-function-attribute_002c-AVR"></a> +</dd> +<dt><code>signal</code></dt> +<dd><p>Use this attribute on the AVR to indicate that the specified +function is an interrupt handler. The compiler generates function +entry and exit sequences suitable for use in an interrupt handler when this +attribute is present. +</p> +<p>See also the <code>interrupt</code> function attribute. +</p> +<p>The AVR hardware globally disables interrupts when an interrupt is executed. +Interrupt handler functions defined with the <code>signal</code> attribute +do not re-enable interrupts. It is save to enable interrupts in a +<code>signal</code> handler. This “save” only applies to the code +generated by the compiler and not to the IRQ layout of the +application which is responsibility of the application. +</p> +<p>If both <code>signal</code> and <code>interrupt</code> are specified for the same +function, <code>signal</code> is silently ignored. +</p></dd> +</dl> + +<hr> +<div class="header"> +<p> +Next: <a href="Blackfin-Function-Attributes.html#Blackfin-Function-Attributes" accesskey="n" rel="next">Blackfin Function Attributes</a>, Previous: <a href="ARM-Function-Attributes.html#ARM-Function-Attributes" accesskey="p" rel="previous">ARM 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="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |