assembler.md

The Assembler

The CPU will begin execution at address 0. There is no special 'main' label - the first thing you write will be the first thing executed.

Instructions and registers are case-insensitive.

Numeric literals

Both decimal and ternary are supported with no prefix.

Comments

Use a semicolon ; to ignore everything following it on that line.

Labels

Use .label on its own line to define a label, which represents the address of the instruction or value following the label.

To use a label's address as an operand, just write its name. You can also write .label[offset].

.main
  JAL .load200
  ; ...

.load200
  MOV a0, 200
  JMP ra

Data

You can declare a place for a single tryte of data by putting $name on its own line. $name[n] declares n trytes of data and can be accessed with $name[offset].

Data is placed at exactly the position it appears in the sourcecode. Make sure you JMP past any data declarations to avoid running data as code.

$player_position[2]

.get_player_pos
  LDA r0, $player_position[0]   ; x
  LDA r1, $player_position[1]   ; y
  JMP ra

Memory-mapped symbols are made available with this syntax also.

Pseudoinstructions

Syntax	Description
NOP	Does nothing
PSH x, y, z, ...	Pushes the given registers to the stack
POP x, y, z, ...	Pops the given registers from the stack in reverse order

Calling convention

This is just a suggestion - there is no obligation to follow it in your code.

Unlike MIPS, subroutines have no obligation to PSH registers they mutate. If you want a register's value saved, PSH it before calling and POP afterwards. However, remember that if a subroutine is calling into another it must PSH ra and POP ra.

Input and ouput should be done through the rX registers, sequentially. It is useful to write a function signature like a, b -> c, d to represent the inputs r0 "a" / r1 "b" and the outputs r0 "c" / r1 "d".

MOV r0, 1
MOV r1, 2
JAL .sum2

; a, b -> sum
.sum2
  ADD r0, r1
	MOV r0, r2
  JMP ra