64 lines
2.2 KiB
Plaintext
64 lines
2.2 KiB
Plaintext
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# MOM , Minimal Object Machine
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This layer sits between the language layer (vool) and the risc machine layer.
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It is meant to make the transition (between vool and risc) easier to understand.
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Previous efforts were doing the transition without an intermediate layer. But while
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this was possible, it was more difficult than need be, and so we go to the old saying
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than everything in computing can be fixed by another layer :-)
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## Recap
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A little recap of why the transition was too steep will naturally reveal the design of MOM.
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### Structure
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Vool has a tree structure. Risc is a linked list, so essentially flat.
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### Memory model
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Vool has no memory, it has objects and they just are. Risc on the other hand has only registers
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and memory. Data can only move to/from/between registers, ie not from memory to memory.
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While Risc knows about objects, it deals in machine words.
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### Execution model
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Vool's implicit execution model would be interpretation, ie tree traversal. Vool has high level
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control structures, including send, and no goto, it is a language after all.
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Risc is close to a cpu, it has a current instruction (pc), registers (8) and a register based
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instruction set. Risc has word comparisons and a jump. Call is not used as the stack is not
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used (stacks are messy, not oo)
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## Design
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The *essential* step from vool to risc, is the one from a language to a machine. From statements
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that hang in the air, to an instruction set.
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So to put a layer in the middle of those two, MOM will be:
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### Tree based
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So almost 1-1 from vool (leave that transformation for next step, which is part of the
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simplification. Flattening needs state to be carried around and so we can do without that)
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### Use object memory
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object to object transfer
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no registers
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### Instruction based
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So a machine than language. No control structures, but compare and jump instructions.
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No send or call, just objects and jump.
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Machine capabilities (instructions) for basic operations. Use of macros for higher level.
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## Outlook
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The next transformation from mom to the Risc layer will naturally include the transformation of:
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- tree to list
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- mom instructions to risc instructions (which is 1 to n so relatively simple)
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- memory to memory transfer, to memory register memory transfers.
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