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Correctly implemented write protection

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Luxferre
2022-08-13 11:49:03 +03:00
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commit 79c0001293
2 changed files with 11 additions and 3 deletions
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README.md
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@@ -54,7 +54,7 @@ Address range|Size (bytes)|Purpose
... |varies |General purpose data (GPD) area
...-0x7dff |varies |Command buffer area
To preserve runtime integrity, Equi implementations are allowed to (but not required to) restrict all writes to the addresses below the GPD area start. Note that command buffer area must not be write-restricted, i.e. Equi programs can be self-modifying. Also, when reading 16-bit from the area below GPD start, only the values at offsets 0x0000 (stack size), 0x0008 (CLT start address), 0x000a (GPD area start address), 0x000c (command buffer start address) and 0x000e (command buffer size) are guaranteed to be populated by the runtime in big-endian, all others will appear in the host endian byte order so the program must not rely on their values in any way.
To preserve runtime integrity, Equi implementations are allowed to (but not required to) restrict all writes to the addresses below the GPD area start. Note that command buffer area must not be write-restricted, i.e. Equi programs can be self-modifying. Also, when reading 16-bit from the area below GPD start, only the values at offsets 0x0000 (stack size), 0x0008 (CLT start address), 0x000c (command buffer start address) and 0x000e (command buffer size) are guaranteed to be populated by the runtime in big-endian, all others will appear in the host endian byte order so the program must not rely on their values in any way. For GPD area start address, better use `G` instruction exclusively.
Equi is strictly case-sensitive: all uppercase basic Latin letters, as well as a number of special characters, are reserved for machine instructions, and all custom words must be defined in lowercase only (additionally, `_` character is allowed in the identifiers). Within comments (see below), any characters can be used.