Monitor program for IBM PC compatibles in 512B
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Juhani Krekelä b434e826fe First commit 1 year ago
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CC0 First commit 1 year ago
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anattos.asm First commit 1 year ago


AnattOS is a 512 byte memory editor with convenience features for hand programming machine code.


256 bytes of memory are show in a 16 by 16 grid. Each line of 16 bytes is checksummed with Fletcher-16, and the checksum is displayed after the line. The address under the cursor is displayed below the memory dump.

If the byte under the cursor begins an instruction where the opcode and mod-r/m bytes' fields have the standard meanings, the fields' meanings are decoded and shown below the address. Note that the case of mod=0 r/m=6 is not special cased, and will display bp for the r/m field.

Arrow keys can be used to navigate the memory, and r to call into the address under the cursor. When returning to AnattOS the code should restore segment registers, direction flag, and stack pointer to the values they had upon entry.


AnattOS is only able to examine first 64KiB of RAM.