hw/i386.reference/s02_06.htm

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   4 <TITLE>80386 Programmer's Reference Manual -- Section 2.6</TITLE>
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   8 Chapter 2 -- Basic Programming Model</A><BR>
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  14 <P>
  15 <H1>2.6  Interrupts and Exceptions</H1>
  16 The 80386 has two mechanisms for interrupting program execution:
  17 <OL>
  18 <LI>Exceptions are synchronous events that are the responses of the CPU
  19 to certain conditions detected during the execution of an instruction.
  20 <LI>Interrupts are asynchronous events typically triggered by external
  21 devices needing attention.
  22 </OL>
  23 Interrupts and exceptions are alike in that both cause the processor to
  24 temporarily suspend its present program execution in order to execute a
  25 program of higher priority. The major distinction between these two kinds of
  26 interrupts is their origin. An exception is always reproducible by
  27 re-executing with the program and data that caused the exception, whereas an
  28 interrupt is generally independent of the currently executing program.
  29 <P>
  30 Application programmers are not normally concerned with servicing
  31 interrupts. More information on interrupts for systems programmers may be
  32 found in
  33 <A HREF="c09.htm">Chapter 9</A>
  34    . Certain exceptions , however, are of interest to
  35 applications programmers, and many operating systems give applications
  36 programs the opportunity to service these exceptions. However, the operating
  37 system itself defines the interface between the applications programs and
  38 the exception mechanism of the 80386.
  39 <P>
  40 Table 2-2 highlights the exceptions that may be of interest to applications
  41 programmers.
  42 <UL>
  43 <LI> A divide error exception results when the instruction
  44 <A HREF="DIV.htm">DIV</A> or
  45 <A HREF="IDIV.htm">IDIV</A> is
  46 executed with a zero denominator or when the quotient is too large for
  47 the destination operand . (Refer to
  48 <A HREF="c03.htm">Chapter 3</A>
  49 for a discussion of <A HREF="DIV.htm">DIV</A>
  50 and <A HREF="IDIV.htm">IDIV</A>.)
  51 <LI> The debug exception may be reflected back to an applications program
  52 if it results from the trap flag (TF).
  53 <LI> A breakpoint exception results when the instruction
  54 <A HREF="INT.htm">INT 3</A> is executed.
  55 This instruction is used by some debuggers to stop program execution at
  56 specific points.
  57 <LI> An overflow exception results when the
  58 <A HREF="INT.htm">INTO</A> instruction is executed
  59 and the OF (overflow) flag is set (after an arithmetic operation that
  60 set the OF flag ) . (Refer to
  61 <A HREF="c03.htm">Chapter 3</A>
  62    for a discussion of <A HREF="INT.htm">INTO</A>) .
  63 <LI> A bounds check exception results when the
  64 <A HREF="BOUND.htm">BOUND</A> instruction is
  65 executed and the array index it checks falls outside the bounds of the
  66 array . (Refer to
  67 <A HREF="c03.htm">Chapter 3</A>
  68    for a discussion of the <A HREF="BOUND.htm">BOUND</A> instruction. )
  69 <LI> Invalid opcodes may be used by some applications to extend the
  70 instruction set. In such a case, the invalid opcode exception presents
  71 an opportunity to emulate the opcode.
  72 <LI> The "coprocessor not available" exception occurs if the program
  73 contains instructions for a coprocessor, but no coprocessor is present
  74 in the system.
  75 <LI> A coprocessor error is generated when a coprocessor detects an illegal
  76 operation.
  77 </UL>
  78 The instruction <A HREF="INT.htm">INT</A> generates an interrupt whenever it is executed; the
  79 processor treats this interrupt as an exception. The effects of this
  80 interrupt (and the effects of all other exceptions) are determined by
  81 exception handler routines provided by the application program or as part of
  82 the systems software (provided by systems programmers). The
  83 <A HREF="INT.htm">INT</A> instruction
  84 itself is discussed in
  85 <A HREF="c03.htm">Chapter 3</A>. Refer to
  86 <A HREF="c09.htm">Chapter 9</A> for a more complete
  87 description of exceptions.
  88 <PRE>
  89 Table 2-2. 80386 Reserved Exceptions and Interrupts
  90
  91 Vector Number      Description
  92
  93 0                  Divide Error
  94 1                  Debug Exceptions
  95 2                  NMI Interrupt
  96 3                  Breakpoint
  97 4                  <A HREF="INT.htm">INTO</A> Detected Overflow
  98 5                  <A HREF="BOUND.htm">BOUND</A> Range Exceeded
  99 6                  Invalid Opcode
 100 7                  Coprocessor Not Available
 101 8                  Double Exception
 102 9                  Coprocessor Segment Overrun
 103 10                 Invalid Task State Segment
 104 11                 Segment Not Present
 105 12                 Stack Fault
 106 13                 General Protection
 107 14                 Page Fault
 108 15                 (reserved)
 109 16                 Coprocessor Error
 110 17-32              (reserved)
 111 </PRE>
 112 <P>
 113 <HR>
 114 <P>
 115 <B>up:</B> <A HREF="c02.htm">
 116 Chapter 2 -- Basic Programming Model</A><BR>
 117 <B>prev:</B> <A HREF="s02_05.htm">2.5  Operand Selection</A><BR>
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 119 <A HREF="c03.htm">Chapter 3 -- Applications Instruction Set</A><BR>
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