rs-vm

Registers

Every register is followed in memory. Exemple: acc is after ip ect.

Order of register is as following: ip, acc, ax, bx, cx, dx, ex, fx, gx, hx, sp, fp.

Special registers

• ip: instruction pointer (16bits) don't touch please
• acc: accumulator, stored results of mathematical operations (add, sub, mul ...)
• sp: stack pointer (handle subroutines)
• fp: frame pointer (pointer inside stack frame)

Normal registers

• a:
  • ax: main register (16bits) can be separated in two 8bits register
  • ah: 8bits register, upper byte of ax
  • al: 8bits register, lower byte of ax
• b: same handling as a with registers bh, bl and bx
• c: same handling as a with registers ch, cl and cx
• d: same handling as a with registers dh, dl and dx
• ex : 16bits register
• fx : 16bits register
• gx : 16bits register
• hx : 16bits register

Instruction

• mov x y (move x in y):
  • x = register, memory (as u8 or u16), literal, register pointer (as u8 or u16), literal + register (as an offset)
  • y = register, memory (as u8 or u16), register pointer (as u8 or u16)
• add x y (add x and y in register acc):
  • x = register
  • y = literal, register
  • x + y > 65535 -> flag Carry == 0100
• sub x y (sub x and y in register acc):
  • x = literal, register
  • y = literal, register
  • x - y < 0 -> flag Carry == 0100
  • x and y can't be both literal
• mult x y (mul x and y in register acc):
  • x = register
  • y = literal, register
  • x * y > 65535 -> flag Carry == 0100
• cmp x y (update flag by comparing x and y):
  • x = register
  • y = literal, register
  • x == y -> flag Zero == 0001
  • x > y -> flag Pos == 0000
  • x < y -> flag Neg == 0010
• inc reg (increment value in reg)
• dec rec (decrement value in reg)
• jmp label (jmp to label unconditionnaly):
  • jmp = jne (jmp if flag Zero is not set)
  • jmp = jeq (jmp if flag Zero is set)
  • jmp = jgt (jmp if flag Zero is not set AND flag Neg is not set)
  • jmp = jge (jmp if flag Neg is not set)
  • jmp = jlt (jmp if flag Neg is set)
  • jmp = jle (jmp if flag Neg is set OR if flag Zero is set)
• psh val (push val on stack):
  • val = register, register pointer (as u8 or u16), literal, memory (as u8 or u16)
• pop val (pop stack in val):
  • val = register, register pointer (as u8 or u16), memory (as u8 or u16)
• cal val (call subroutine, setting up stackframe):
  • val = label or register
• ret (return from subroutine, restoring stackframe)
• xor x y (xor x and y and store result in x):
  • x = register
  • y = literal or register
• end (end of program)

Memory map

0x3000-0x4000 -> screen