lostecho/oldlinux-files
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

add directory study

Browse Source
This commit is contained in:
gohigh
2024-02-19 00:25:23 -05:00
parent b1306b38b1
commit f3774e2f8c
4001 changed files with 2285787 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

51
study/Ref-docs/manual Intel386/I386Manual/S16_02.HTM Normal file
View File

@@ -0,0 +1,51 @@
<html><!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html>
<head>
<title>80386 Programmer's Reference Manual -- Section 16.2</title>
</head>
<body>
<b>up:</b> <a href="C16.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/C16.HTM">Chapter 16 -- Mixing 16-Bit and 32 Bit Code</a><br>
<b>prev:</b> <a href="S16_01.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/S16_01.HTM">16.1 How the 80386 Implements 16-Bit and 32-Bit Features</a><br>
<b>next:</b> <a href="S16_03.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/S16_03.HTM">16.3 Sharing Data Segments Among Mixed Code Segments</a>
<p>
<hr>
<p>
<h1>16.2 Mixing 32-Bit and 16-Bit Operations</h1>
The 80386 has two instruction prefixes that allow mixing of 32-bit and 16-bit operations within one segment:
<ul>
<li>The operand-size prefix (66H)
<li>The address-size prefix (67H)
</ul>
<p>These prefixes reverse the default size selected by the D-bit. For example, the processor can interpret the word-move instruction <a href="MOV.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/MOV.HTM">MOV</a> mem, reg in any of four ways:
<ul>
<li>In a USE32 segment:
<ol>
<li>Normally moves 32 bits from a 32-bit register to a 32-bit effective address in memory.
<li>If preceded by an operand-size prefix, moves 16 bits from a 16-bit register to 32-bit effective address in memory.
<li>If preceded by an address-size prefix, moves 32 bits from a 32-bit register to a16-bit effective address in memory.
<li>If preceded by both an address-size prefix and an operand-size prefix, moves 16 bits from a 16-bit register to a 16-bit effective address in memory.
</ol>
<li>In a USE16 segment:
<ol>
<li>Normally moves 16 bits from a 16-bit register to a 16-bit effective address in memory.
<li>If preceded by an operand-size prefix, moves 32 bits from a 32-bit register to 16-bit effective address in memory.
<li>If preceded by an address-size prefix, moves 16 bits from a 16-bit register to a32-bit effective address in memory.
<li>If preceded by both an address-size prefix and an operand-size prefix, moves 32 bits from a 32-bit register to a 32-bit effective address in memory.
</ol>
</ul>
These examples illustrate that any instruction can generate any combination of operand size and address size regardless of whether the instruction is in a USE16 or USE32 segment. The choice of the USE16 or USE32 attribute for a code segment is based upon these criteria:
<ol>
<li>The need to address instructions or data in segments that are larger than 64 Kilobytes.
<li>The predominant size of operands.
<li>The addressing modes desired. (Refer to <a href="C17.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/C17.HTM">Chapter 17</a> for an explanation of the additional addressing modes that are available when 32-bit addressing is used.)
</ol>
Choosing a setting of the D-bit that is contrary to the predominant size of operands requires the generation of an excessive number of operand-size prefixes.
<p>
<hr>
<p><b>up:</b> <a href="C16.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/C16.HTM">Chapter 16 -- Mixing 16-Bit and 32 Bit Code</a><br>
<b>prev:</b> <a href="S16_01.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/S16_01.HTM">16.1 How the 80386 Implements 16-Bit and 32-Bit Features</a><br>
<b>next:</b> <a href="S16_03.HTM" tppabs="http://webster.cs.ucr.edu/Page_TechDocs/Doc386/S16_03.HTM">16.3 Sharing Data Segments Among Mixed Code Segments</a>
</body>