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https://github.com/freem/asm6f

A fork of loopy's ASM6, a 6502 assembler.
https://github.com/freem/asm6f

6502 assembler famicom nes

Last synced: 3 months ago
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A fork of loopy's ASM6, a 6502 assembler.

Host: GitHub
URL: https://github.com/freem/asm6f
Owner: freem
Created: 2013-12-13T05:40:13.000Z (about 11 years ago)
Default Branch: master
Last Pushed: 2023-08-23T03:08:13.000Z (over 1 year ago)
Last Synced: 2024-09-30T06:01:50.237Z (3 months ago)
Topics: 6502, assembler, famicom, nes
Language: C
Homepage:
Size: 309 KB
Stars: 94
Watchers: 6
Forks: 23
Open Issues: 15
Metadata Files:
- Readme: readme-original.txt

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README

--------------------------------------------------------------
ASM6 (v1.6)
A 6502 assembler by loopy (loopy at mm.st)
--------------------------------------------------------------

Yes, it's another 6502 assembler. I built it to do NES development, but you
can probably use it for just about anything. Why use this instead of one of
the other zillion assemblers out there? I don't know, but choice is good,
right? :) I wrote it because I thought most others were either too finicky,
had weird syntax, took too much work to set up, or too bug-ridden to be useful.

This is free software. You may use, modify, and / or redistribute any part
of this software in any fashion.

--------------------------------------------------------------
Command line
--------------------------------------------------------------

Usage:

asm6 [-options] sourcefile [outputfile] [listfile]

Options:

-? Show some help
-l Create listing
-L Create verbose listing (expand REPT, MACRO)
-d: Define a symbol and make it equal to 1
-q Quiet mode (suppress all output unless there's an error)
Default output is .bin
Default listing is .lst

--------------------------------------------------------------
Syntax
--------------------------------------------------------------

Comments begin with a semicolon (;). A colon (:) following a label is
optional.

examples:

lda #$00 ;hi there
label1: jmp label2
label2 beq label1

--------------------------------------------------------------
Numbers and expressions
--------------------------------------------------------------

Hexadecimal numbers begin with '$' or end with 'h'. Binary numbers begin
with '%' or end with 'b'. Characters and strings are surrounded by
single or double quotes. The characters (' " \) within quotes must be
preceded by a backslash (\).

examples:

12345
'12345'
$ABCD
0ABCDh
%01010101
01010101b

Supported operators (listed by precedence):

( )
(unary) + - ~ ! < >
* / %
+ -
<< >>
< > <= >=
= == != <>
&
^
|
&&
||

'=' and '<>' are equivalent to C's '==' and '!=' operators. The unary '<'
and '>' operators give the lower and upper byte of a 16-bit word (respectively).
All other operators function like their C equivalents.

--------------------------------------------------------------
Labels
--------------------------------------------------------------

Labels are case sensitive. The special '$' label holds the current program
address. Labels beginning with '@' are local labels. They have limited scope,
visible only between non-local labels. Names of local labels may be reused.

label1:
@tmp1:
@tmp2:
label2:
@tmp1:
@tmp2:

Labels beginning with one or more '+' or '-' characters are nameless labels,
especially useful for forward and reverse branches.

example:

-- ldx #0
- lda $2002 ;loop (wait for vblank)
bne -
- lda $2002 ;nameless labels are easy to reuse..
bne -

cpx #69
beq + ;forward branch..
cpx #96
beq +here ;use more characters to make more unique

jmp -- ;multiple --'s handy for nested loops
+ ldx #0
+here nop

--------------------------------------------------------------
Assembler directives (in no particular order)
--------------------------------------------------------------

All directives are case insensitive and can also be preceded by a period (.)

EQU

For literal string replacement, similar to #define in C.

one EQU 1
plus EQU +
DB one plus one ;DB 1 + 1

Unlike EQU, statements with '=' are evaluated to a number first.
Also unlike EQU, symbols created with '=' can be reused.

i=1
j EQU i+1
k=i+1 ;k=1+1
i=j+1 ;i=i+1+1
i=k+1 ;i=2+1

INCLUDE (also INCSRC)

Assemble another source file as if it were part of the current
source.

INCLUDE whatever.asm

INCBIN (also BIN)

Add the contents of a file to the assembly output.

moredata: INCBIN whatever.bin

An optional file offset and size can be specified.

INCBIN foo.bin, $400 ;read foo.bin from $400 to EOF
INCBIN foo.bin, $200, $2000 ;read $2000 bytes, starting from $200

DB, DW (also BYTE/WORD, DCB/DCW, DC.B/DC.W)

Emit byte(s) or word(s). Multiple arguments are separated by
commas. Strings can be "shifted" by adding a value to them (see
example).

DB $01,$02,$04,$08
DB "ABCDE"+1 ;equivalent to DB "BCDEF"
DB "ABCDE"-"A"+32 ;equivalent to DB 32,33,34,35,36

DL, DH

Similar to DB, outputting only the LSB or MSB of a value.

DL a,b,c,d ;equivalent to DB a, >b, >c, >d

HEX

Compact way of laying out a table of hex values. Only raw hex values
are allowed, no expressions. Spaces can be used to separate numbers.

HEX 456789ABCDEF ;equivalent to DB $45,$67,$89,$AB,$CD,$EF
HEX 0 1 23 4567 ;equivalent to DB $00,$01,$23,$45,$67

DSB, DSW (also DS.B/DS.W)

Define storage (bytes or words). The size argument may be followed
by a fill value (default filler is 0).

DSB 4 ;equivalent to DB 0,0,0,0
DSB 8,1 ;equivalent to DB 1,1,1,1,1,1,1,1
DSW 4,$ABCD ;equivalent to DW $ABCD,$ABCD,$ABCD,$ABCD

PAD

Fill memory from the current address to a specified address. A fill
value may also be specified.

PAD $FFFA ;equivalent to DSB $FFFA-$
PAD $FFFA,$EA ;equivalent to DSB $FFFA-$,$EA

ORG

Set the starting address if it hasn't been assigned yet, otherwise
ORG functions like PAD.

ORG $E000 ;start assembling at $E000
.
.
.
ORG $FFFA,$80 ;equivalent to PAD $FFFA,$80

ALIGN

Fill memory from the current address to an N byte boundary. A fill
value may also be specified.

ALIGN 256,$EA

FILLVALUE

Change the default filler for PAD, ALIGN, etc.

FILLVALUE $FF

BASE

Set the program address. This is useful for relocatable code,
multiple code banks, etc. The same can also be accomplished by
assigning the '$' symbol directly (i.e. '$=9999').

oldaddr=$
BASE $6000
stuff:
.
.
.
BASE oldaddr+$-stuff

IF / ELSEIF / ELSE / ENDIF

Process a block of code if an expression is true (nonzero).

IF j>0
DB i/j
ELSE
DB 0
ENDIF

IFDEF / IFNDEF

Process a block of code if a symbol has been defined / not defined.

IFDEF _DEBUG_
.
.
.
ENDIF

MACRO / ENDM

MACRO name args...

Define a macro. Macro arguments are comma separated.
Labels defined inside macros are local (visible only to that macro).

MACRO setAXY x,y,z
LDA #x
LDX #y
LDY #z
ENDM

setAXY $12,$34,$56
;expands to LDA #$12
; LDX #$34
; LDY #$56

REPT / ENDR

Repeat a block of code a specified number of times.
Labels defined inside REPT are local.

i=0
REPT 256
DB i
i=i+1
ENDR

ENUM / ENDE

Reassign PC and suppress assembly output. Useful for defining
variables in RAM.

ENUM $200
foo: db 0
foo2: db 0
ENDE

ERROR

Stop assembly and display a message.

IF x>100
ERROR "X is out of range :("
ENDIF

--------------------------------------------------------------