MastroVM is a Virtual Machine (and fantasy CPU) that is made to be simple and easy to use.

• 128 KB of memory
• 16 Registers (a, b, c and so on)
• I/O Ports (keyboard only for now)
• TVO (Text Video Output)
• 256 Entries for stack
• 19 Instructions

Mastro has 19 instructions, here's all of them:

• mov [ADDR] VAL | [ADDR] REG | REG [ADDR] | REG VAL | REG REG
• push [ADDR] | VAL | REG
• pop REG
• jmp [ADDR]
• je [ADDR]
• jne [ADDR]
• jle [ADDR]
• jl [ADDR]
• jge [ADDR]
• jg [ADDR]
• cmp [ADDR] VAL | [ADDR] REG | REG [ADDR] | REG VAL | REG REG
• add [ADDR] VAL | [ADDR] REG | REG [ADDR] | REG VAL | REG REG
• dec [ADDR] VAL | [ADDR] REG | REG [ADDR] | REG VAL | REG REG
• mul [ADDR] VAL | [ADDR] REG | REG [ADDR] | REG VAL | REG REG
• div [ADDR] VAL | [ADDR] REG | REG [ADDR] | REG VAL | REG REG
• in REG VAL | REG REG
• out VAL VAL | REG VAL | VAL REG| REG REG
• call [ADDR]
• ret

As you can see in the mov instruction, we can't mov an address directly into another, that's because you have to use an intermediate register to do that, for example:

mov regA [0x0042]
mov [0x0040] regA

Same thing applies for cmp, add, dec, mul and div

In MastroVM you can't do something like

mov [sp - 4] 0x0042

This is because my CPU and Assembler doesn't support this type of arithmetic yet, here's what you can do instead:

dec sp 4
mov [sp] 0x0042
add sp 4

Whenever you call a subroutine in MastroVM, it will do the following things:

• Push current address to the stack
• Jmp to the address So remember to ALWAYS return a subroutine, or else, it will never... return!

call printChar
mov regA 0x42

.:
 jmp .

printChar:
 mov [0x3a2f] 0x64
 ret

Let's say you want to define a string to use it later, in Mastro, you would do it in the following way:

str wd "Hello World!"

mov regB str            ; Moves the address of str into regB
mov regC [regB]         ; Moves the first letter of str into regC
mov [0x3a2f] regC       ; Moves the contents of regC to TVO address
; This will print 'H' to the screen

Remember to ALWAYS define the string BEFORE you use it!

The memory layout in Mastro looks like this:

- Free Memory: from 0x0000 until 0x41ff (16 kb)
- TVO: 0x3a2f until 0x41ff (80 * 25 chars)
- Stack: from 0x41ff until 0x42ff (256 entries of 16 bits data)
- Rodata: from 0x42ff until 0x817f (16KB of rodata)
- ROM: from 0x817f until 0xffff (32 kb)

And the current ports are:

port[0] = Keyboard status (set if key pressed)
port[1] = Key that is being pressed
port[2] = cursor X
port[3] = cursor Y

• Going to put known bugs here.