damonpalovaara/rust-simple-vm

Simple VM

A simple 16-bit virtual machine, written to learn Rust basics.

Technical Details

This machine has 8 registers:

• A, B, C and M are general purpose
• SP is the stack pointer
• BP is the base pointer for function frames
• PC is the program counter
• FLAGS contains 16 status bits, these are currently undefined and always 0

Registers are 16-bits. Memory is accessed with 16-bit addresses, meaning there is are 65536 bytes of addressable memory.

Instructions

Instructions are 16-bits and have the following bit format:

[ O O O O O O O O | A A A A B B B B ]

Here, O is the operation (eg PUSH or ADD). A and B are arguments to that operation, and in some cases are combined into a single 8-bit value.

Operation	A	B	Description
Nop	-	-	Do nothing
Push	8bit literal	Join with A	Push literal to stack
PopRegister	Register	-	Pop value to register
AddStack	-	-	Pop 2 values, push their sum
AddRegister	Register	Register	A = A + B