34 lines
2.2 KiB
Markdown
34 lines
2.2 KiB
Markdown
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# The processor
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This processor is a stack-based, big-endian custom processor. Its purpose is to execute [bytecode][bin_file] independently of the actual platform. Its stack-based design is kinda inspied by the Java VM, but don't quote me on that.
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## The stack
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This processor is equipped with a 256-slot stack, capable of holding both floating-point decimal numbers and integral numbers with 32-bit precision.
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The stack is the destination to all result values from instructions and the source of input values if not explicitly supplied from registers.
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There are 5 different operations possible on the stack:
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1. Push: Adds an element to the top of the stack
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2. Pop: Removes and retrieves the element currently on top of the stack
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3. Dup: Duplicates the element currently on top of the stack, effectively `push`-ing it twice
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4. Swap: Swaps the two highest elements currently on the stack
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5. Top: Returns the number of elements currently in the stack
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## The registers
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This processor is equipped with 256 registers, `#00` through `#ff` and `#00` holds the program counter, or `PC`.
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Just like the stack, each register can hold a 32-bit number which can be either a floating-point decimal number or an integral number.
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Their purpose is to store information to be used in instructions instead of having to deal with stack push and pop.
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## The MMU
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This processor is equipped with a Memory Management Unit, or `MMU`.
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This MMU is used each time the processor tries to access memory, be it instruction data, sprites, files, VRAM, etc.
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Contrary to standard memory managers, this MMU uses segmented memory instead of paginated memory to save as much RAM as possible on the host system.
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The MMU defines three access permissions on each segment, and attempting to use them while they are absent will result in an interrupt being thrown.
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1. Readable
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2. Writable
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3. Executable
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Segments in this MMU may refer to actual RAM, the stack, VRAM or even files.
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The MMU handles segments in two different ways: if the data is in actual host RAM, then the segment is `present` and if it isn't, then the segment is `absent` and accessed through getters and setters.
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[bin_file]: ./bin_file.md
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