1<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>5.4.�Interrupt Vectors and Handlers</title><link rel="stylesheet" href="cs.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.74.0"><link rel="home" href="index.html" title="Sourcery CodeBench Lite"><link rel="up" href="chap-cs3.html" title="Chapter�5.�CS3™: The CodeSourcery Common Startup Code Sequence"><link rel="prev" href="sec-cs3-memory-layout.html" title="5.3.�Memory Layout"><link rel="next" href="sec-cs3-supported-boards.html" title="5.5.�Supported Boards for ARM EABI"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">5.4.�Interrupt Vectors and Handlers</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="sec-cs3-memory-layout.html">Prev</a>�</td><th width="60%" align="center">Chapter�5.�CS3™: The CodeSourcery Common Startup Code Sequence</th><td width="20%" align="right">�<a accesskey="n" href="sec-cs3-supported-boards.html">Next</a></td></tr></table><hr></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sec-cs3-interrupts"></a>5.4.�Interrupt Vectors and Handlers</h2></div></div></div><p> 2 CS3 provides standard handlers for interrupts, exceptions and 3 traps, but also allows you to define your own handlers as needed. 4 In this section, we use the term 5 <em class="firstterm">interrupt</em> as a generic term for this 6 entire class of events. 7 </p><p> 8 Different processors handle interrupts in various ways, but 9 there are two general approaches: 10 </p><div class="itemizedlist"><ul type="disc"><li><p> 11 Some processors fetch an address from an array indexed by 12 the interrupt number, and jump to that address. We call 13 these <em class="firstterm">address vector</em> processors. 14 </p></li><li><p> 15 Others multiply the interrupt number by some constant 16 factor, add a base address, and jump directly to that 17 address. Here, the interrupt vector consists of blocks of 18 code, so we call these <em class="firstterm">code vector</em> 19 processors. 20 </p></li><li><p> 21 Still other processors use a more complicated descriptor 22 mechanism for the interrupt table. 23 </p></li></ul></div><p> 24 25 <span> 26 M-profile processors like the Cortex-M3 use the address vector 27 model. Classic ARM processors (including ARM7/ARM9 as well as 28 Cortex-A/R series processors) are technically code vector processors. 29 However, each vector slot only holds a single instruction. CS3 30 emulates the address vector model on these processors by placing an 31 indirect branch instruction in each slot of the real exception vector. 32 </span> 33 34 35 36 37 38 39 40 41 42 43 The remainder of this section assumes that you have some understanding 44 of the specific requirements for your target; refer to the architecture 45 manuals if necessary. 46 </p><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id526335"></a>5.4.1.�ARM EABI Interrupt Vector Implementation</h3></div></div></div><p> 47 On address vector processors, the CS3 library provides an array 48 of pointers to interrupt handlers named 49 <code class="varname">__cs3_interrupt_vector_<em class="replaceable"><code>form</code></em></code>, 50 where <em class="replaceable"><code>form</code></em> identifies the particular 51 processor variant the vector is appropriate for. 52 Each entry in the vector holds a reference to a symbol named 53 <code class="function">__cs3_isr_<em class="replaceable"><code>name</code></em></code>, 54 where <em class="replaceable"><code>name</code></em> is the customary name of 55 that interrupt on the processor, or a number if there is no 56 consistently used name. 57 You can find the interrupt vector details in 58 <a class="xref" href="sec-cs3-vector-tables.html" title="5.6.�Interrupt Vector Tables">Section�5.6, “Interrupt Vector Tables”</a>. The particular 59 vector used by a given CS3-supported board is documented 60 in the tables in <a class="xref" href="sec-cs3-supported-boards.html" title="5.5.�Supported Boards for ARM EABI">Section�5.5, “Supported Boards for ARM EABI”</a>. 61 </p><p> 62 CS3 provides a reasonable default definition for each 63 <code class="function">__cs3_isr_<em class="replaceable"><code>name</code></em></code> 64 handler. Many of these symbols are aliased to a 65 common handler routine. If your program stops at a default 66 interrupt handler, its name as shown in backtraces may therefore 67 not correctly reflect which interrupt occurred. 68 </p><p> 69 To override an individual handler, provide your own definition 70 for the appropriate 71 <code class="function">__cs3_isr_<em class="replaceable"><code>name</code></em></code> 72 symbol. The definition need not be placed in any particular 73 object file section. 74 </p><p> 75 To override the entire interrupt vector, you can define 76 <code class="varname">__cs3_interrupt_vector_<em class="replaceable"><code>form</code></em></code>. 77 You must place this definition in a section named 78 <code class="literal">.cs3.interrupt_vector</code>. The linker script 79 reports an error if the <code class="literal">.cs3.interrupt_vector</code> 80 section is empty, to ensure that the definition of 81 <code class="varname">__cs3_interrupt_vector_<em class="replaceable"><code>form</code></em></code> 82 occupies the proper section. 83 </p><p> 84 You may define the vector in C with an array of pointers using 85 the <code class="literal">section</code> attribute to place it in the 86 appropriate section. For example, to override the interrupt 87 vector on Altera Cyclone III Cortex-M1 boards, make the following definition: 88 </p><pre class="programlisting">typedef void handler(void); 89handler *__attribute__((section (".cs3.interrupt_vector"))) 90 __cs3_interrupt_vector_micro[] = 91{ ... };</pre><p> 92 </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="sec-cs3-interrupt-handlers"></a>5.4.2.�Writing Interrupt Handlers</h3></div></div></div><p> 93 Interrupt handlers typically require special call/return and 94 register usage conventions that are target-specific and beyond 95 the scope of this document. In many cases, normal C functions 96 cannot be used as interrupt handlers. 97 <span> 98 For example, the EABI requires that the stack be 8-byte aligned, 99 but on some ARMv7-M processors, only 4-byte stack alignment 100 is guaranteed when calling an interrupt vector. This can cause 101 subtle runtime failures, usually when 8-byte types are used. 102 </span> 103 </p><p> 104 As an alternative to writing interrupt handlers in assembly language, 105 on ARM targets they may be written in C using the 106 <code class="literal">interrupt</code> 107 108 attribute. This tells the compiler to generate appropriate function 109 entry and exit sequences for an interrupt handler. 110 <span> 111 For example, to override the 112 <code class="function">__cs3_isr_nmi</code> handler, 113 use the following definition: 114 <pre class="programlisting">void __attribute__ ((interrupt)) __cs3_isr_nmi (void) 115{ 116 ... custom handler code ... 117}</pre> 118 </span> 119 <span> 120 On ARM targets, the <code class="literal">interrupt</code> attribute also 121 takes an optional parameter to specify the type of interrupt. 122 </span> 123 124 Refer to the GCC manual for more details about attribute syntax 125 and usage. 126 </p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="sec-cs3-memory-layout.html">Prev</a>�</td><td width="20%" align="center"><a accesskey="u" href="chap-cs3.html">Up</a></td><td width="40%" align="right">�<a accesskey="n" href="sec-cs3-supported-boards.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">5.3.�Memory Layout�</td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top">�5.5.�Supported Boards for ARM EABI</td></tr></table></div></body></html> 127