Hello everyone and welcome to my blog.
This week we continued to learn and practice assembly language math operations using 6502 processor.
Last week we managed to understand how to turn screen into coordinates, use these coordinates for drawing and how to use keyboard to control drawing. This week we tried to create a bouncing object. With help of some example code and logic provided by our teacher we were able to build a bouncing object.
First we created an object, then we made it move and bounce off the side 45 degrees. We managed to separate the movement of the object into Y and X. Then we would increment or decrement if the object reached one or another side. Of course, we were far from the end but it was just the beginning.
Our logic was far from correct, the screen would not clear so we copied some clearing logic from "Etch-a-Sketch" example code and implemented it in our game. We also made our code slow down a little bit so it was easy to follow. Next, we started to work on the paddle. We had to create some logic to create the paddle itself and to make logic for bouncing of the object from the paddle. After that we have done some more improvements and clearing.
Working on this project increased my knowledge of assembly, although I still feel a little bit confused when working with it. Maybe I will be able to practice it a little bit more in my free time to deeper my understanding of the subject. Overall, my experience was interesting and valuable, I understood how some things work behind in the processor.
The complete code for the pong game looks like this:
; zero-page variable locations
define ROW $20 ; current row
define COL $21 ; current column
define DELTAX $30 ; current Delta X
define DELTAY $31 ; current Delta Y
define BOUNCEX $35 ; checks if X has bounced
define BOUNCEY $36 ; checks if Y has bounced
define VELX $38
define VELY $39
define POINTER $10 ; ptr start of row
define POINTER_H $11
define PADDLEL $40
define paddleR $41
define SCORE $24
define HIT $23
; constants
define DOT $01 ; dot colour
define PADDLE $07 ; black colour
ldy #$00 ; put help text on screen
print: lda help,y
beq setup
sta $f000,y
iny
bne print
setup: lda #$0f ; set initial ROW,COL
sta ROW
lda #$00
sta COL
lda #$20
sta VELX
lda #$20
sta VELY
lda #$0B
sta PADDLEL
lda #$15
sta PADDLER
lda #$00
sta SCORE
draw: lda ROW ; ensure ROW is in range 031
and #$1f
sta ROW
lda COL ; ensure COL is in range 031
and #$1f
sta COL
ldy ROW ; load POINTER with start-of-row
lda table_low,y
sta POINTER
lda table_high,y
sta POINTER_H
ldy COL ; store CURSOR at POINTER plus COL
lda #DOT
sta (POINTER),y
drawPaddle:
ldy #$1f ; load POINTER with start-of-row
lda table_low,y
sta POINTER
lda table_high,y
sta POINTER_H
ldy PADDLEL ; store CURSOR at POINTER plus COL
lda #PADDLE
paddleLoop:
sta (POINTER),y
iny
cpy PADDLER
bne paddleLoop
colidR: lda COL
cmp #$1F
bne colidL
sta BOUNCEY
colidL: lda COL
cmp #$00
bne colidD
sta BOUNCEY
colidD: lda ROW
cmp #$1F
bne colidU
CLC
jmp gameover
colidU: lda ROW
cmp #$00
bne colidP
sta BOUNCEX
colidP: CLC
lda ROW
cmp #$1E
bne incScore
lda COL
cmp PADDLEL
bcc incScore
cmp PADDLER
bcs incScore
sta BOUNCEX
inc HIT
lda $fe ;randomize vel when hitting paddle
cmp #$80 ;ensure vel isn't too high
bcc velx
adc #$81
velx:
sta VELX
lda $fe
sta VELY
incScore:
CLC
lda ROW
cmp #$1D
bne delaya
lda HIT
cmp #$00
beq delaya
lda #$00
sta HIT
SED
CLC
lda SCORE
adc #$01
sta SCORE
CLD
delaya: ldy #$00 ; Delay processor to slow down game
ldx #$00
delay: iny
cpy #$FF
bne delay
ldy #$00
inx
cpx #$06
bne delay
ballX: lda VELX
adc DELTAX
sta DELTAX
bcc ballY
ldy ROW ; load POINTER with start-of-row
lda table_low,y
sta POINTER
lda table_high,y
sta POINTER_H
ldy COL ; store CURSOR at POINTER plus COL
lda #00
sta (POINTER),y
CLC
lda BOUNCEX
cmp #$00
bne decROW
incROW: inc ROW
CLC
bcc ballY
decROW: dec ROW
ballY:
lda VELY
adc DELTAY
sta DELTAY
bcc getkey
ldy ROW ; load POINTER with start-of-row
lda table_low,y
sta POINTER
lda table_high,y
sta POINTER_H
ldy COL ; store CURSOR at POINTER plus COL
lda #00
sta (POINTER),y
CLC
lda BOUNCEY
cmp #$00
bne decCOL
incCOL: inc COL
CLC
bcc getkey
decCOL: dec COL
getkey: lda $ff ; get a keystroke
ldx #$00 ; clear out the key buffer
stx $ff
cmp #$83 ; check key == LEFT
bne checkR
ldy PADDLEL
cpy #$00
beq checkR
ldy #$1f ; load POINTER with start-of-row
lda table_low,y
sta POINTER
lda table_high,y
sta POINTER_H
ldy PADDLER ; store CURSOR at POINTER plus COL
dey
lda #00
sta (POINTER),y
dec PADDLEL
dec PADDLER
jmp done
checkR: cmp #$81 ; check key == RIGHT
bne done
ldy PADDLER
cpy #$20
beq done
ldy #$1f ; load POINTER with start-of-row
lda table_low,y
sta POINTER
lda table_high,y
sta POINTER_H
ldy PADDLEL ; store CURSOR at POINTER plus COL
lda #00
sta (POINTER),y
inc PADDLEL
inc PADDLER
done:
ldy #$0
scorePrint:
lda score,y
beq scoreNum
sta $f0F0,y
iny
bne scorePrint
scoreNum:
lda SCORE
and #$F0
LSR
LSR
LSR
LSR
TAY
lda number,y
sta $f0f8
lda SCORE
and #$0F
TAY
lda number,y
sta $f0f9
lda SCORE
clc ; repeat
jmp draw
gameover:
brk
clear: lda table_low ; clear the screen
sta POINTER
lda table_high
sta POINTER_H
ldy #$00
tya
c_loop: sta (POINTER),y
iny
bne c_loop
inc POINTER_H
ldx POINTER_H
cpx #$06
bne c_loop
jmp setup
; these two tables contain the high and low bytes
; of the addresses of the start of each row
table_high:
dcb $02,$02,$02,$02,$02,$02,$02,$02
dcb $03,$03,$03,$03,$03,$03,$03,$03
dcb $04,$04,$04,$04,$04,$04,$04,$04
dcb $05,$05,$05,$05,$05,$05,$05,$05,
table_low:
dcb $00,$20,$40,$60,$80,$a0,$c0,$e0
dcb $00,$20,$40,$60,$80,$a0,$c0,$e0
dcb $00,$20,$40,$60,$80,$a0,$c0,$e0
dcb $00,$20,$40,$60,$80,$a0,$c0,$e0
; help message on character screen
help:
dcb "A","r","r","o","w",32,"k","e","y","s"
dcb 32,"C","o","n","t","r","o","l",32,"p","a","d"
dcb "d","l","e"
dcb 00
score:
dcb "S","C","O","R","E",":",32
dcb 00
number:
dcb "0","1","2","3","4","5","6","7"
dcb "8","9","A","B","C","D","E","F"
dcb 00
This week we continued to learn and practice assembly language math operations using 6502 processor.
Last week we managed to understand how to turn screen into coordinates, use these coordinates for drawing and how to use keyboard to control drawing. This week we tried to create a bouncing object. With help of some example code and logic provided by our teacher we were able to build a bouncing object.
First we created an object, then we made it move and bounce off the side 45 degrees. We managed to separate the movement of the object into Y and X. Then we would increment or decrement if the object reached one or another side. Of course, we were far from the end but it was just the beginning.
Our logic was far from correct, the screen would not clear so we copied some clearing logic from "Etch-a-Sketch" example code and implemented it in our game. We also made our code slow down a little bit so it was easy to follow. Next, we started to work on the paddle. We had to create some logic to create the paddle itself and to make logic for bouncing of the object from the paddle. After that we have done some more improvements and clearing.
Working on this project increased my knowledge of assembly, although I still feel a little bit confused when working with it. Maybe I will be able to practice it a little bit more in my free time to deeper my understanding of the subject. Overall, my experience was interesting and valuable, I understood how some things work behind in the processor.
The complete code for the pong game looks like this:
; zero-page variable locations
define ROW $20 ; current row
define COL $21 ; current column
define DELTAX $30 ; current Delta X
define DELTAY $31 ; current Delta Y
define BOUNCEX $35 ; checks if X has bounced
define BOUNCEY $36 ; checks if Y has bounced
define VELX $38
define VELY $39
define POINTER $10 ; ptr start of row
define POINTER_H $11
define PADDLEL $40
define paddleR $41
define SCORE $24
define HIT $23
; constants
define DOT $01 ; dot colour
define PADDLE $07 ; black colour
ldy #$00 ; put help text on screen
print: lda help,y
beq setup
sta $f000,y
iny
bne print
setup: lda #$0f ; set initial ROW,COL
sta ROW
lda #$00
sta COL
lda #$20
sta VELX
lda #$20
sta VELY
lda #$0B
sta PADDLEL
lda #$15
sta PADDLER
lda #$00
sta SCORE
draw: lda ROW ; ensure ROW is in range 031
and #$1f
sta ROW
lda COL ; ensure COL is in range 031
and #$1f
sta COL
ldy ROW ; load POINTER with start-of-row
lda table_low,y
sta POINTER
lda table_high,y
sta POINTER_H
ldy COL ; store CURSOR at POINTER plus COL
lda #DOT
sta (POINTER),y
drawPaddle:
ldy #$1f ; load POINTER with start-of-row
lda table_low,y
sta POINTER
lda table_high,y
sta POINTER_H
ldy PADDLEL ; store CURSOR at POINTER plus COL
lda #PADDLE
paddleLoop:
sta (POINTER),y
iny
cpy PADDLER
bne paddleLoop
colidR: lda COL
cmp #$1F
bne colidL
sta BOUNCEY
colidL: lda COL
cmp #$00
bne colidD
sta BOUNCEY
colidD: lda ROW
cmp #$1F
bne colidU
CLC
jmp gameover
colidU: lda ROW
cmp #$00
bne colidP
sta BOUNCEX
colidP: CLC
lda ROW
cmp #$1E
bne incScore
lda COL
cmp PADDLEL
bcc incScore
cmp PADDLER
bcs incScore
sta BOUNCEX
inc HIT
lda $fe ;randomize vel when hitting paddle
cmp #$80 ;ensure vel isn't too high
bcc velx
adc #$81
velx:
sta VELX
lda $fe
sta VELY
incScore:
CLC
lda ROW
cmp #$1D
bne delaya
lda HIT
cmp #$00
beq delaya
lda #$00
sta HIT
SED
CLC
lda SCORE
adc #$01
sta SCORE
CLD
delaya: ldy #$00 ; Delay processor to slow down game
ldx #$00
delay: iny
cpy #$FF
bne delay
ldy #$00
inx
cpx #$06
bne delay
ballX: lda VELX
adc DELTAX
sta DELTAX
bcc ballY
ldy ROW ; load POINTER with start-of-row
lda table_low,y
sta POINTER
lda table_high,y
sta POINTER_H
ldy COL ; store CURSOR at POINTER plus COL
lda #00
sta (POINTER),y
CLC
lda BOUNCEX
cmp #$00
bne decROW
incROW: inc ROW
CLC
bcc ballY
decROW: dec ROW
ballY:
lda VELY
adc DELTAY
sta DELTAY
bcc getkey
ldy ROW ; load POINTER with start-of-row
lda table_low,y
sta POINTER
lda table_high,y
sta POINTER_H
ldy COL ; store CURSOR at POINTER plus COL
lda #00
sta (POINTER),y
CLC
lda BOUNCEY
cmp #$00
bne decCOL
incCOL: inc COL
CLC
bcc getkey
decCOL: dec COL
getkey: lda $ff ; get a keystroke
ldx #$00 ; clear out the key buffer
stx $ff
cmp #$83 ; check key == LEFT
bne checkR
ldy PADDLEL
cpy #$00
beq checkR
ldy #$1f ; load POINTER with start-of-row
lda table_low,y
sta POINTER
lda table_high,y
sta POINTER_H
ldy PADDLER ; store CURSOR at POINTER plus COL
dey
lda #00
sta (POINTER),y
dec PADDLEL
dec PADDLER
jmp done
checkR: cmp #$81 ; check key == RIGHT
bne done
ldy PADDLER
cpy #$20
beq done
ldy #$1f ; load POINTER with start-of-row
lda table_low,y
sta POINTER
lda table_high,y
sta POINTER_H
ldy PADDLEL ; store CURSOR at POINTER plus COL
lda #00
sta (POINTER),y
inc PADDLEL
inc PADDLER
done:
ldy #$0
scorePrint:
lda score,y
beq scoreNum
sta $f0F0,y
iny
bne scorePrint
scoreNum:
lda SCORE
and #$F0
LSR
LSR
LSR
LSR
TAY
lda number,y
sta $f0f8
lda SCORE
and #$0F
TAY
lda number,y
sta $f0f9
lda SCORE
clc ; repeat
jmp draw
gameover:
brk
clear: lda table_low ; clear the screen
sta POINTER
lda table_high
sta POINTER_H
ldy #$00
tya
c_loop: sta (POINTER),y
iny
bne c_loop
inc POINTER_H
ldx POINTER_H
cpx #$06
bne c_loop
jmp setup
; these two tables contain the high and low bytes
; of the addresses of the start of each row
table_high:
dcb $02,$02,$02,$02,$02,$02,$02,$02
dcb $03,$03,$03,$03,$03,$03,$03,$03
dcb $04,$04,$04,$04,$04,$04,$04,$04
dcb $05,$05,$05,$05,$05,$05,$05,$05,
table_low:
dcb $00,$20,$40,$60,$80,$a0,$c0,$e0
dcb $00,$20,$40,$60,$80,$a0,$c0,$e0
dcb $00,$20,$40,$60,$80,$a0,$c0,$e0
dcb $00,$20,$40,$60,$80,$a0,$c0,$e0
; help message on character screen
help:
dcb "A","r","r","o","w",32,"k","e","y","s"
dcb 32,"C","o","n","t","r","o","l",32,"p","a","d"
dcb "d","l","e"
dcb 00
score:
dcb "S","C","O","R","E",":",32
dcb 00
number:
dcb "0","1","2","3","4","5","6","7"
dcb "8","9","A","B","C","D","E","F"
dcb 00
Comments
Post a Comment