Eight-Op Turing VM

Turing Complete VM with 8 Instructions

About

Eight operation 32-bit VM with 80k memory (32-bit boundaries, so essentially 20k) preinitialized to 0.

Ten Registers (0-9) that point to memory locations, all start at location 0.

Technically Turing Complete.

Operations

• INC Register# - Increments the value a register is pointing to by 1
• DEC Register# - Decrements the value a register is pointing to by 1
• NEXT Register# - Sets register pointer to next memory location
• PREV Register# - Sets register pointer to previous memory location
• PUTC Register# - Displays value of register to screen as an 8bit Char.
• GETC Register# - Stores single char from stdin to memory location
• CMP RegisterA# RegisterB# - Compares RegisterA to RegisterB, sets zero flag to true if they are equal
• JE LabelName - Jump to label if previous compare was equal
• LABEL LabelName - Not an operation, just sets memory location for jump command

Macros

The "compiler" supports 2 macros, which requires a period to pre-pended to the command:

• .PRELOAD 00,01,33,A,1,0x45 - Comma separated values to preload into memory starting at location 0.
  • Values with single characters are treated as CHAR
  • Values with more than one character are treated as INT, unless 'x' is found as the second char, then treated as HEX integer
• .CODE_SEGMENT - Tells compiler where the start of the code is. Implicitly defined as 0, but if using PRELOAD macro, it needs to be explicity defined.

Comments

Comments in code cannot be inline, they must be on a separate line starting with a semi-colon ';'

Sample Code

; This will display text to the screen
.PRELOAD !,H,e,l,l,o,32,W,o,r,l,d,!
.CODE_SEGMENT
; Set Register 0 to next location in memory, location of 'H'
NEXT 0
LABEL printMessage
PUTC 0
NEXT 0
; Compare Reg 1 and Reg 0, Register 1 is at location 0, which is '!'
CMP 1 0
; If they are equal, that means we are done printing the text
JE complete
; If we get here, we need to unconditionally jump, so cmp a register to itself.
CMP 1 1
JE printMessage
LABEL complete

Architecture

• Write code in simple, but irritating assembly-style language
• Feed into pseudo-compiler, which converts each command into 32-bit wide bytecode
• Opcodes are fed into the VM
• VM interprets and processes instructions. Program counter increments until out of instructions, after which the program ends.
• Any error is thrown as runtime exception and will dump a stack trace.