hw/i386.reference/s14_03.htm

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   4 <TITLE>80386 Programmer's Reference Manual -- Section 14.3</TITLE>
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   7 <B>up:</B> <A HREF="c14.htm">
   8 Chapter 14 -- 80386 Real-Address Mode</A><BR>
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  14 <H1>14.3  Interrupt and Exception Handling</H1>
  15 Interrupts and exceptions in 80386 real-address mode work as much as they
  16 do on an 8086. Interrupts and exceptions vector to interrupt procedures via
  17 an interrupt table. The processor multiplies the interrupt or exception
  18 identifier by four to obtain an index into the interrupt table. The entries
  19 of the interrupt table are far pointers to the entry points of interrupt or
  20 exception handler procedures. When an interrupt occurs, the processor
  21 pushes the current values of CS:IP onto the stack, disables interrupts,
  22 clears TF (the single-step flag), then transfers control to the location
  23 specified in the interrupt table. An <A HREF="IRET.htm">IRET</A> instruction at the end of the
  24 handler procedure reverses these steps before returning control to the
  25 interrupted procedure.
  26 <P>
  27 The primary difference in the interrupt handling of the 80386 compared to
  28 the 8086 is that the location and size of the interrupt table depend on the
  29 contents of the IDTR (IDT register). Ordinarily, this fact is not apparent
  30 to programmers, because, after RESET, the IDTR contains a base address of 0
  31 and a limit of 3FFH, which is compatible with the 8086. However, the
  32 <A HREF="LGDT.htm">LIDT</A>
  33 instruction can be used in real-address mode to change the base and limit
  34 values in the IDTR . Refer to
  35 <A HREF="c09.htm">Chapter 9</A>
  36    for details on the IDTR , and the
  37 <A HREF="LGDT.htm">LIDT</A> and <A HREF="SGDT.htm">SIDT</A> instructions.
  38 If an interrupt occurs and the corresponding
  39 entry of the interrupt table is beyond the limit stored in the IDTR, the
  40 processor raises exception 8.
  41 <P>
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  43 <P>
  44 <B>up:</B> <A HREF="c14.htm">
  45 Chapter 14 -- 80386 Real-Address Mode</A><BR>
  46 <B>prev:</B> <A HREF="s14_02.htm">14.2  Registers and Instructions</A><BR>
  47 <B>next:</B> <A HREF="s14_04.htm">14.4  Entering and Leaving Real-Address Mode</A>
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