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311 lines
13 KiB
HTML
311 lines
13 KiB
HTML
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<title>Address Tables - SourceGen Tutorial</title>
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<body>
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6502bench
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<a id="topnav-home" href="/">HOME</a>
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<a id="topnav-sgtutorial" class="active" href="/sgtutorial">SourceGen Tutorial</a>
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<!-- START: sidenav-incl.html active:#sidenav-address-tables -->
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<ul>
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<li id="sidenav-index"><a href="./">Introduction</a></li>
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<li id="sidenav-about-disasm"><a href="about-disasm.html">About Disassembly</a></li>
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<li id="sidenav-using-sourcegen"><a href="using-sourcegen.html">Using SourceGen</a>
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<ul>
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<li id="sidenav-moving-around"><a href="moving-around.html">Moving Around</a></li>
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<li id="sidenav-simple-edits"><a href="simple-edits.html">Simple Edits</a></li>
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<li id="sidenav-labels-symbols"><a href="labels-symbols.html">Labels & Symbols</a></li>
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<li id="sidenav-editing-data"><a href="editing-data.html">Editing Data Operands</a></li>
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<li id="sidenav-string-formatting"><a href="string-formatting.html">String Formatting</a></li>
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</div>
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<div id="main">
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<h2>Address Tables</h2>
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<div class="grid-container">
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<div class="grid-item-text">
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<p>Code often contains tables of addresses to code or data.
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Formatting them one at a time can be tedious, so SourceGen
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provides a faster way. For this tutorial we'll start by labeling
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and tagging a single entry by hand, then do the rest in one shot.</p>
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<p>Start a new project. Select the Apple //e platform, click
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<samp>Select File</samp> and navigate to the 6502bench Examples directory.
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In the "A2-Amper-fdraw" directory, select the file "AMPERFDRAW#061d60"
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(just ignore the existing .dis65 file).
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Click <samp>OK</samp> to create the project.</p>
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</div>
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</div>
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<div class="grid-container">
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<div class="grid-item-image">
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<img src="images/t3-initial.png" alt="t3-initial"/>
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</div>
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<div class="grid-item-text">
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<p>Not a lot to see here -- just half a dozen lines of loads and stores,
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then nothing but data.
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This particular program interfaces with Applesoft BASIC, so we can make it
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a bit more meaningful by loading an additional platform
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symbol file.</p>
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</div>
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</div>
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<div class="grid-container">
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<div class="grid-item-image">
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<img src="images/t3-a2-props.png" alt="t3-a2-props"/>
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</div>
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<div class="grid-item-text">
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<p>Select <samp>Edit > Project Properties</samp>, then the
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<samp>Symbol Files</samp> tab. Click <samp>Add Symbol Files from Runtime</samp>.
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The file browser starts in the "RuntimeData" directory.
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Open the "Apple" folder, then select "Applesoft.sym65",
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and click <samp>Open</samp>. Click <samp>OK</samp> to close
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the project properties window.</p>
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</div>
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</div>
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<div class="grid-container">
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<div class="grid-item-image">
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<img src="images/t3-amperv.png" alt="t3-amperv"/>
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</div>
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<div class="grid-item-text">
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<p>The <code>STA</code> instructions now reference <code>BAS_AMPERV</code>,
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which is noted as a code vector. We can see the code setting up a jump
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(opcode $4C) to $1D70.</p>
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</div>
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</div>
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<div class="grid-container">
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<div class="grid-item-image">
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<img src="images/t3-1d70.png" alt="t3-1d70"/>
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</div>
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<div class="grid-item-text">
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<p>As it happens, the start address of the code
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is $1D60 -- the last four digits of the filename -- so let's make that
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change. Double-click the initial <code>.ORG</code> statement,
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and change it from $2000 to $1D60. We can now see that $1D70 starts
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right after this initial chunk of code.</p>
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</div>
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</div>
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<div class="grid-container">
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<div class="grid-item-image">
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<img src="images/t3-1d70-code.png" alt="t3-1d70-code"/>
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</div>
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<div class="grid-item-text">
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<p>Select the line with address $1D70, then
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<samp>Actions > Tag Address As Code Start Point</samp>.
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More code appears, but not much -- if you scroll down you'll see that most
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of the file is still data.</p>
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<p>The code at $1D70 searches through a table at
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$1D88 for a match with the contents of the accumulator. If it finds a match,
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it loads bytes from tables at $1DA6 and $1D97, pushes them on the stack,
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and then <code>JMP</code>s away. This code is pushing a return address onto the stack.
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When the code at <code>BAS_CHRGET</code> returns, it'll return to that
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address. Because of a quirk of the 6502 architecture, the address pushed
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must be the desired address minus one.</p>
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</div>
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</div>
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<div class="grid-container">
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<div class="grid-item-image">
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<img src="images/t3-1d97.png" alt="t3-1d97"/>
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</div>
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<div class="grid-item-text">
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<p>The first byte in the first address table at $1D97 (which
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has the auto-label <code>L1D97</code>) is $B4.
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The first byte in the second table is $1D. So the first
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address we want is $1DB4 + 1 = $1DB5.</p>
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</div>
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</div>
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<div class="grid-container">
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<div class="grid-item-image">
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<img src="images/t3-1d97-edit.png" alt="t3-1d97-edit.png"/>
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</div>
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<div class="grid-item-text">
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<p>Select the line at $1DB5, and use
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<samp>Actions > Tag Address As Code Start Point</samp>.
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More code appears, but again it's only a few lines. Let's dress this one
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up a bit. Set a label on the code at $1DB5 called "<kbd>FUNC</kbd>".
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Then, at $1D97, edit the data item (double-click on "<samp>$B4</samp>"),
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click <samp>Single bytes</samp>, then type "<kbd>FUNC</kbd>"
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(note the text field gets focus immediately, and the radio button
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automatically switches to <samp>symbolic reference</samp> when you start typing).
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Click <samp>OK</samp>.</p>
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</div>
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</div>
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<div class="grid-container">
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<div class="grid-item-image">
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<img src="images/t3-1d97-post.png" alt="t3-1d97-post.png"/>
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</div>
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<div class="grid-item-text">
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<p>The operand at $1D97 should now say <code><FUNC-1</code>.
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Repeat the process at $1DA6, this time clicking the <samp>High</samp>
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part radio button below the symbol entry text box,
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to make the operand there say <code>>FUNC</code>. (If it says
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<code><FUNC-152</code>, you forgot to select the high part.)</p>
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<p>We've now changed the first entry in the address table to a
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symbolic reference, which is helps someone reading the code to
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understand what is being referenced. You could repeat these
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steps (tag as code, set label, change address bytes to symbols)
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for the remaining items, but there's an easier way.</p>
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</div>
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</div>
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<div class="grid-container">
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<div class="grid-item-image">
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<img src="images/t3-format-dialog.png" alt="t3-format-dialog"/>
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</div>
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<div class="grid-item-text">
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<p>Click on the line at address $1D97, then shift-click the line at
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address $1DA9 (which should be <code>.FILL 12,$1e</code>). Select
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<samp>Actions > Format Address Table</samp>.</p>
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<p>Contrary to first impressions, this imposing dialog does not allow you
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to launch objects into orbit. There are a variety of common ways to
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structure an address table, all of which are handled here. You can
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configure the various parameters and see the effects as you make
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each change.</p>
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</div>
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</div>
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<div class="grid-container">
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<div class="grid-item-image">
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<img src="images/t3-format-cfg.png" alt="t3-format-cfg"/>
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</div>
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<div class="grid-item-text">
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<p>The message at the top should indicate that there are 30 bytes
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selected. In <samp>Address Characteristics</samp>, click the
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<samp>Parts are split across sub-tables</samp> checkbox and the
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<samp>Adjusted for RTS/RTL</samp> checkbox.
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As soon as you do, the first line of the <samp>Generated Addresses</samp>
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list should show the symbol "<code>FUNC</code>".
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The rest of the addresses will look like
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"<code>(+) T1DD0</code>". The "(+)" means that a label was not found at
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that location, so a new global label will be generated automatically.</p>
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<p>Down near the bottom, check the
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<samp>Tag targets as code start points</samp> checkbox.
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Because we saw the table contents being pushed onto the stack for
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<code>RTS</code>, we know that they're all code entry points.</p>
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<p>Click <samp>OK</samp>.</p>
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</div>
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</div>
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<div class="grid-container">
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<div class="grid-item-image">
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<img src="images/t3-format-done.png" alt="t3-format-done"/>
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</div>
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<div class="grid-item-text">
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<p>The table of address bytes at $1D97 should now all be
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references to symbols -- 15 low parts followed by 15 high parts. If you
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scroll down, you should see nothing but instructions until you get to the
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last dozen bytes at the end of the file. (If this isn't the case, use
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<samp>Edit > Undo</samp>, then work through the steps again.)</p>
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</div>
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</div>
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<div class="grid-container">
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<div class="grid-item-text">
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<p>The formatter did the same series of actions you went through earlier,
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<!-- set a
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label, apply the label to the low and high bytes in the table, add a
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code start point tag -->
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but applied them to multiple locations in one shot. The next step in
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the disassembly process would be to rename the "Tnnnn" labels to
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something more meaninful.</p>
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<p>We don't want to save this project, so select
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<samp>File > Close</samp>. When SourceGen asks for confirmation,
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click <samp>Discard & Continue</samp>.</p>
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</div>
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</div>
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</div> <!-- #main -->
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