2.0 KiB
SlotMachine
This layer sits between the language layer (sol) and the risc machine layer. It is meant to make the transition (between sol and risc) easier to understand.
Previous efforts were doing the transition without an intermediate layer. But while this was possible, it was more difficult than need be, and so we go to the old saying that everything in computing can be fixed by another layer :-)
Recap
A little recap of why the transition was too steep will naturally reveal the design of SlotMachine.
Structure
Sol has a tree structure. Risc is a linked list, so essentially flat.
Memory model
Sol has no memory, it has objects and they just are. Risc on the other hand has only registers and memory. Data can only move to/from/between registers, ie not from memory to memory. While Risc knows about objects, it deals in machine words.
Execution model
Sol's implicit execution model would be interpretation, ie tree traversal. Sol has high level control structures, including send, and no goto, it is a language after all.
Risc is close to a cpu, it has a current instruction (pc), registers (8) and a register based instruction set. Risc has word comparisons and a jump. Call is not used as the stack is not used (stacks are messy, not oo)
Design
The essential step from sol to risc, is the one from a language to a machine. From statements that hang in the air, to an instruction set. So to put a layer in the middle of those two, SlotMachine will be:
Linked list
But, very much like Risc, just higher level so it's easier to understand
Use object memory
object to object transfer
no registers (one could see the current message as the only register)
Instruction based
So SlotMachine is a machine layer, rather than a language. No control structures, but compare and jump instructions.
No send or call, just objects and jump.
Again in two steps, see below
Machine capabilities (instructions) for basic operations. Use of macros for higher level.