Virtual Machine

Basic virtual machine based on Von Neumann architecture. Implemented specific assembler that compiles code into binary file that could be executed by virtual machine.

Usage

vnvm assembler <code.asm> [out.bin] - build binary file from assembler code vnvm exec <filename.bin> - execute binary file

Assembler

List of assembler comands:

Commands take variables, constants or functions' names as arguments. In commands with two arguments (except load) first argument has only one byte to code address of variable and second argument has two bytes to code address. So first variable should be defined as global, otherwise an error is likely to appear.

• push <src> - push src to programm stack
• pop <dst> - pop the top of programm stack and write it to dst
• call <function> - push instruction pointer of next line to programm stack and call function
• exec <function> - just call function without pushing anything to stack
• copy <src> <dst> - copy from src to dst
• load <src> <dst> - copy from src to dst, however here src has larger address that dst
• add <src> <dst> - add src to dst and write result to dst
• sub <src> <dst> - substract src from dst and write result to dst
• isequal <var1> <var2> - push the result of var1 == var2 to programm stack
• if <flag> - if flag is true (equals 1), then execute next line, else skip next line
• return - pop the top of programm stack and return to the address written in popped top
• exit - exit programm, the return code is written to instruction pointer
• print <var> - print integer variable var on new line
• printconst <const> - print string constant const on new line
• scan <var> - read integer variable var from input

Code structure:

var {
    var 0
    another_var 17
    ...
}
const {
    string Here's a string
    hello_world Hello, World!
    ...
}
def {
    function {
        static {
            static_var 10
            ...
        }
        <commands>
        ...
        push &static_var
        add var &static_var
        ...
        return
    }
    ...
    main {
        static {
            static_var 15
            ...
        }
        <commands>
        ...
        exit
    }
}

• var { ... } - definition of global integer variables, template for each line is <name> <value>
• const { ... } - definition of global string constants, template for each line is <name> <string>
• def { ... } - definition of functions, including main, which is an entry point of programm
  • <function_name> { ... } - definition of function function_name
    • static { ... } - definition of static integer variables, template for each line is <name> <value>
    • the rest part of function is its code, static variables should be used in code with & before name