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Préface et documents
Architecture
Spécifications résumées
Architecture, Memory Map
BIOS
Structure des ROMs
Structure des CDs
Registres RAM
Vidéo
Système vidéo
Les palettes
Le fix
Les sprites
Audio
Système audio
Communication Z80
YM2610: ADPCM et SSG
Les pistes CDDA
Developpement
L'ASM 68K
Outils
Devkit ASM
Erreurs courantes
Portage MVS / NGCD
Electronique
Electronique
Cartouche flash MVS
Problèmes de lecteur CD
Productions
Astrosmash
Unleashed
Knackiballs
Bootloader et cable NGCD

Test MVS #01

L'assembleur 68K

Superbes cours en ligne: http://atariste.free.fr/asm/assembleur.html

16 registres: d0-d7, a0-a7, tous de 4 octets (longwords).
a7: stack pointer
Taille des opérations: b (byte), w (word), l (long).
Address space de 24bits ($FFFFFF)
SR: Status register (16 bits), MSB: system byte, LSB: user byte.

Immediate addressing: move.b #1,d0

Register addressing: move.l d0,d1

Absolute addressing: mode d0,$100000 (en mémoire)

Pointer addressing:
movea.l #$FF0000,a0
move.w #1, (a0)

Pointer relative addressing: (offest de -$8000 à $7FFF)
movae.l #$FF0000,a0
move.w #1, (a0) ;store the number 1 at memory location $FF0000
move.w #1, 2(a0) ;store the number 1 at memory location $FF0002

PC Relative Addressing:
move.w #1, $100(pc) ;stores the value 1 at the memory location $100 bytes from the current instruction.

Pointer Addressing with Predecrement/Postincrement:
movea.l #$FF0000, a0
move.b #7, (a0)+ ;store 7 at $FF0000 and add 1 to a0, a0 now equals $FF0001
move.b #4, (a0)+ :store 4 at $FF0001 and add 1 to a0
move.w #3, (a0)+ ;store 3 at $FF0002 and add 2 to a0
move.l #9, (a0)+ ;store 9 at $FF0004, a0 is now equal to $FF0008
move.w #6, -(a0) ;store 7 at $FF0006

BEQ: Si Zero
BNE: Si pas Zero

Byte writes to any even address store the same data to the MSB and LSB:

Byte writes to any odd address are ignored.
Byte reads from any even address return the MSB of the 16-bit data from that register:

move.b $3C0002, d0 : Data read is $AB where word in VRAM is $ABCD

Byte reads from any odd address return the last value on the 68K data bus:

move.b $3C0003, d0 : Data read is $71
nop : Opcode is $4E71

For example, if we want to push D0.W (with this I mean D0, the lower 16 bits) we just MOVE.W D0,-(A7).
And to pop it back, just MOVE.W (A7)+,D0. Remember that when popping a word, the upper 16 bits in D0 is still there.

movem d0-d4/a0-a2,-(a7) and then movem (a7)+,d0-d4/a0-a2

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