2021-01-21 13:40:28 +01:00
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
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<title>.</title>
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</head><body>
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<p><span class="h1">Internals: The Retro Image</span>
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<br/><br/>
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2021-05-17 19:04:42 +02:00
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The actual Retro language is stored as a memory image for Nga.
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2021-01-21 13:40:28 +01:00
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<br/><br/>
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<span class="h2">Format</span>
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<br/><br/>
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The image file is a flat, linear sequence of signed 32-bit
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values. Each value is stored in little endian format. The
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size is not fixed. An interface should check when loading to
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ensure that the physical image is not larger than the emulated
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memory.
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<br/><br/>
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<span class="h2">Header</span>
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<br/><br/>
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The image will start with two cells. The first is a liju....
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instruction, the second is the target address for the jump.
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This serves to skip over the rest of the data and reach the
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actual entry point.
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<br/><br/>
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This is followed by a pointer to the most recent dictionary
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header, a pointer to the next free address in memory, and
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2021-05-17 19:04:42 +02:00
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then the Retro version number.
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<br/><br/>
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<tt class='indentedcode'>| Offset | Contains |</tt>
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<tt class='indentedcode'>| ------ | --------------------------- |</tt>
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<tt class='indentedcode'>| 0 | lit call nop nop |</tt>
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<tt class='indentedcode'>| 1 | Pointer to main entry point |</tt>
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<tt class='indentedcode'>| 2 | Dictionary |</tt>
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<tt class='indentedcode'>| 3 | Heap |</tt>
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<tt class='indentedcode'>| 4 | Retro version |</tt>
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<br/><br/>
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The actual code starts after this header.
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<br/><br/>
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The version number is the year and month. As an example,
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the 12.2019.6 release will have a version number of
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<span class="tt">201906</span>.
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<br/><br/>
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<span class="h2">Layout</span>
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<br/><br/>
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Assuming an Nga built with 524287 cells of memory:
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<br/><br/>
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<tt class='indentedcode'>| RANGE | CONTAINS |</tt>
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<tt class='indentedcode'>| --------------- | ---------------------------- |</tt>
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<tt class='indentedcode'>| 0 - 1024 | Retro Core kernel |</tt>
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<tt class='indentedcode'>| 1025 - 1535 | token input buffer |</tt>
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<tt class='indentedcode'>| 1536 + | start of heap space |</tt>
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<tt class='indentedcode'>| ............... | free memory for your use |</tt>
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<tt class='indentedcode'>| 506879 | buffer for string evaluate |</tt>
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<tt class='indentedcode'>| 507904 | temporary strings (32 * 512) |</tt>
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<tt class='indentedcode'>| 524287 | end of memory |</tt>
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<br/><br/>
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The buffers at the end of memory will resize when specific
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variables related to them are altered.
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</p>
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</body></html>
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