i386/i386.reference/s10_01.htm

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   4 <TITLE>80386 Programmer's Reference Manual -- Section 10.1</TITLE>
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   8 Chapter 10 -- Initialization</A><BR>
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  13 <P>
  14 <H1>10.1  Processor State After Reset</H1>
  15 The contents of EAX depend upon the results of the power-up self test. The
  16 self-test may be requested externally by assertion of BUSY# at the end of
  17 RESET. The EAX register holds zero if the 80386 passed the test. A nonzero
  18 value in EAX after self-test indicates that the particular 80386 unit is
  19 faulty. If the self-test is not requested, the contents of EAX after RESET
  20 is undefined.
  21 <P>
  22 DX holds a component identifier and revision number after RESET as
  23 <A HREF="#fig10-1">Figure 10-1</A>
  24   illustrates. DH contains 3, which indicates an 80386 component. DL
  25 contains a unique identifier of the revision level.
  26 <P>
  27 Control register zero (CR0) contains the values shown in
  28 <A HREF="#fig10-2">Figure 10-2</A>
  29   . The
  30 ET bit of CR0 is set if an 80387 is present in the configuration (according
  31 to the state of the ERROR# pin after RESET). If ET is reset, the
  32 configuration either contains an 80287 or does not contain a coprocessor. A
  33 software test is required to distinguish between these latter two
  34 possibilities.
  35 <P>
  36 The remaining registers and flags are set as follows:
  37 <PRE>
  38    EFLAGS             =00000002H
  39    IP                 =0000FFF0H
  40    CS selector        =000H
  41    DS selector        =0000H
  42    ES selector        =0000H
  43    SS selector        =0000H
  44    FS selector        =0000H
  45    GS selector        =0000H
  46    IDTR:
  47               base    =0
  48               limit   =03FFH
  49 </PRE>
  50 All registers not mentioned above are undefined.
  51 <P>
  52 These settings imply that the processor begins in real-address mode with
  53 interrupts disabled.
  54 <P>
  55 <A NAME="fig10-1">
  56 <IMG align=center SRC="fig10-1.gif" border=0>
  57 <HR>
  58 <A NAME="fig10-2">
  59 <IMG align=center SRC="fig10-2.gif" border=0>
  60 <P>
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