53 lines
1.8 KiB
Text
53 lines
1.8 KiB
Text
# Internals: The Retro Image
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The actual RETRO language is stored as a memory image for Nga.
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## Format
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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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## Header
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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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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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then the RETRO version number.
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| Offset | Contains |
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| ------ | --------------------------- |
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| 0 | lit call nop nop |
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| 1 | Pointer to main entry point |
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| 2 | Dictionary |
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| 3 | Heap |
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| 4 | RETRO version |
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The actual code starts after this header.
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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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`201906`.
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## Layout
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Assuming an Nga built with 524287 cells of memory:
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| RANGE | CONTAINS |
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| --------------- | ---------------------------- |
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| 0 - 1024 | RETRO Core kernel |
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| 1025 - 1535 | token input buffer |
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| 1536 + | start of heap space |
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| ............... | free memory for your use |
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| 506879 | buffer for string evaluate |
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| 507904 | temporary strings (32 * 512) |
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| 524287 | end of memory |
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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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