This chapter documents the Backend for the TR3200 cpu.

@section Legal

    This module is written in 2014 by Luis Panadero Guarde@~no and
    is covered by the vasm copyright without modifications.


@section General

This backend accepts TR3200 instructions as described in the
@uref{https://github.com/trillek-team/trillek-computer, TR3200 specification}

The target address type is 32 bits.

Default alignment for sections is 4 bytes. Instructions alignment is 4 bytes.
Data is aligned to its natural alignment by default, i.e. 2 byte wide data
alignment is 2 bytes and 4 byte wide data alignment is 4 byte.

The backend uses TR3200 syntax! This means the left operands are always the
destination and the right operand is the source (except for single operand
instructions). Register names have to be prefixed by a '@code{%}'
(@code{%bp}, @code{%r0}, etc.)
This means that it should accept WaveAsm assembly files if oldstyle syntax module
is being used. The instructions are lowercase, @option{-dotdir} option is being used
and directives are not in the first column.

@section Extensions

Predefined register symbols in this backend:

@itemize @minus
@item register by number: @code{r0 r1 r2 r3 r4 r5 r6 r7 r8 r9 r10 r11 r12 r13 r14 r15}
@item special registers by name: @code{bp sp y ia flags}
@end itemize

@section Known Problems

    Some known problems of this module at the moment:

@itemize @minus

@item This module need to be fully checked, but has been tested building a full
      program that could be found here : @uref{https://github.com/Zardoz89/trillek-firmware}

@item Instruction relocations are missing.

@end itemize


@section Error Messages

This module has the following error messages:

@itemize @minus
@item 2001: illegal operand
@item 2002: illegal qualifier <%s>
@item 2003: data size not supported
@end itemize

@section Example

It follows a little example to illustrate TR3200 assembly using
the oldstyle syntax module (option @option{-dotdir} required):

@example
const   .equ 0xBEBACAFE           ; A constant
an_addr .equ 0x100                ; Other constant

; ROM code
      .org 0x100000
      .text
_start                            ; Label with or without a ending ":"
      mov %sp, 0x1000             ; Set the initial stack

      mov %r0, 0
      mov %r1, 0xA5
      mov %r2, 0
      storeb %r0, an_addr, %r1

      add %r0, %r2, %bp
      add %r0, %r2, 0
      add %r0, %r0, 10
      add %r0, %r0, 10h
      add %r0, %r0, 0x100010
      add %r0, %r0, (256 + 100)   ; vasm parses math expressions

      mov %r2, 0
      mov %r3, 0x10200

      loadb %r6, 0x100200
      loadb %r1, %r2, 0x100200
      loadb %r1, %r2, %r3
      loadb %r4, var1

      push %r0
      .repeat 2                 ; directives to repeat stuff!
      push const
      .endrepeat

      .repeat 2
      pop %r5
      .endrepeat
      pop %r0

      rcall foo                 ; Relative call/jump!
      sleep

foo:      ; Subrutine
      ifneq %r5, 0
        mul %r5, %r5, 2
      sub %r5, %r5, 1

      ret

; ROM data
      .org 0x100500
var1  .db 0x20                  ; A byte size variable
      .even                     ; Enforce to align to even address
var3  .dw 0x1020                ; A word size variable
var4  .dd 0x0A0B0C20            ; A double word size variable
str1  .asciiz "Hello world!"    ; ASCII string with null termination
str2  .string "Hello world!"    ; ASCII string with null termination
      .fill 5, 0xFF             ; Fill 5 bytes with 0xFF
      .reserve 5                ; Reserves space for 5 byte

@end example
