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@ogamespec ogamespec released this 01 Sep 11:16
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Breakasm

As simple and dumb assembler as possible, to generate code.

To run:

Breakasm test.asm test.prg

PRG file is always 64 Kbytes (the size of 6502 address space). The current assembly pointer (ORG) can be set anywhere in the PRG.

Syntax

The source text is split into lines of the following format:

[LABEL:] COMMAND [OPERAND1, OPERAND2, OPERAND3] ; Comments

The label (LABEL) is optional. The command (COMMAND) contains 6502 instruction or one of the assebmler directives. The operands depend on the command.

Embedded Directives

Directive Description
ORG Set the current PRG assembly position.
DEFINE Define a simple constant
BYTE Output a byte or string
WORD Output uint16_t in little-endian order. You can use both numbers as well as labels and addresses.
END Finish the assembling
PROCESSOR Defines type of processor for informational purposes

Example Source Code

Not to write too much, I will just show you an example of the source code. Do it the same way and it should work.

; Test program

LABEL1:

    PROCESSOR 6502
;    ORG     $100

    DEFINE  KONST   #5

    LDX     KONST

AGAIN:
    NOP
    LDA     SOMEDATA, X         ; Load some data
    JSR     ADDSOME             ; Call sub
    STA     $12, X
    CLC
    BCC     AGAIN               ; Test branch logic

ADDSOME:                        ; Test ALU
    ADC     KONST
    PHP                         ; Test flags in/out
    PLP
    RTS

    ASL     A

SOMEDATA:
    BYTE    12, $FF, "Hello, world" 
    WORD    AGAIN

END

Support for NES and mappers

Dragging some NES and mapper prisserans into a generalized assembler is a bad idea.

Build multiple PRG files and compile a .nes file from them yourself if you need to.

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