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crc b5e26d5284 documentation corrections, updates 
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2021-05-17 17:04:42 +00:00

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