[help] Assembly and bB custom kernel

[Leonardo Santiago]

 

For about a month I have been studying a little bit of Assembly through the great material gathered on the Random Terrain website. (https://www.randomterrain.com/atari-2600-memories.html#assembly_language)

 

Although I managed to create my own kernel, several parts of it I still don't understand. And instead of spending effort with such deep learning, I researched if it was possible to simply create a kernel for batariBasic and continue programming in bB.

 

I found this post which presents a way to use a custom kernel.

 

With some modifications I got to this version below. It's a 2LK and I'm trying to use the same variables as bB to control the players, but this is the problem: I can't (I don't have enough knowledge) use the players pointer correctly. Could anyone clarify my ideas?

 

Player0Draw = $A4			; I'm not using the vars (0-47)
Player1Draw = $A5
BackgroundPtr = $A6 ; $A7


.customdrawscreen


custom_eat_overscan
	;bB code runs during overscan. We wait for overscan to finish so the
	;frame timing doesn't get screwed up.
	lda INTIM
	bmi custom_eat_overscan

custom_do_vertical_sync
	;just a standard vsync
        lda #2
        sta WSYNC ;one line with VSYNC
        sta VSYNC ;enable VSYNC
        sta WSYNC ;one line with VSYNC
        sta WSYNC ;one line with VSYNC
        lda #0
        sta WSYNC ;one line with VSYNC
        sta VSYNC ;turn off VSYNC

custom_setup_vblank_timing
	;use bB timing variables so it should work with both PAL and NTSC
        ifnconst vblank_time
        lda #42+128
        else
        lda #vblank_time+128
        endif
        sta TIM64T

	; feel free to throw useful pre-kernel code in here, so long as it 
	; completes before vblank is over.

custom_eat_vblank
	;wait for vblank to complete
	lda INTIM
	bmi custom_eat_vblank
	lda #0
	sta WSYNC
	sta VBLANK

custom_setup_visible_timing
	;my preference is to use TIM64T to ensure a full screen is drawn.
	lda #230
	sta TIM64T





;------------------------------------------------------------------------------

    ; Desenha a parte superior da tela
    ; 192 - 22 scanlines = 192 - (11*2) = 170
        lda #$02        ; Cor cinza no PF
        sta COLUPF      ; COR no PF 

        lda #1          ; 
        sta CTRLPF      ; Liga o REFLECT 

        ldx #11
UpperSection:
        sta WSYNC

        lda customPFPattern,x
        sta PF0 
        sta PF1
        sta PF2    

        lda customPFColor,x
        sta COLUBK          

        sta WSYNC
        dex
        bne UpperSection

        stx PF0
        stx PF1
        stx PF2


        ; y position
        lda #80
        adc player0height
        sbc player0y
        sta Player0Draw

        

;------------------------------------------------------------------------------
;-- AREA DE JOGO
;------------------------------------------------------------------------------
    ; Desenha a área de jogo
    ; 170 - 160 scanlines = 170 - (80*2) = 10 (base ... not implemented)

        ldy #80             ; Carrega o y com o tamanho da área de jogo

KernelLoop:                 ;   15 - todal de 15 ciclos, vindos do bne KernelLoop
    ; Continuação da segunda linha do 2LK
    ; precalcula os dados usados na primeiralinha do 2LK

        lda player0height   ; 2 17 - altura do Player0 - IMPORTANTE!! este valor deve ser altura-1
        dcp Player0Draw     ; 5 22 - Decrementa Player0Draw e compara com a altura
        bcs DoDrawGrp0      ; 2 24 - (3 25) se o Carry estiver setado, player0 está na scanline atual
        lda #0              ; 2 27 -    caso contrário, desliga o player0
        .byte $2C           ; 4 31 - $2C = BIT with absolute addressing, trick that
                            ;        causes the lda (HumanPtr),y to be skipped
DoDrawGrp0:                 ;   25 - 25 ciclos do pior caso na linha bcs DoDrawGrp0
        lda (player0pointer),y  ; 5 30 - carrega o formato do player0 <<----------------------------- It's not working

        sta WSYNC           ; 3 33 - Aguarda o fim da scanline


    ;-------------------------------------------------
    ; começo da primeira linha do 2LK

        sta GRP0                ; 3  3 - @ 0-22, desenha o player0 efetivamente (entre os ciclos 0 e 22)

        lda (BackgroundPtr),y   ; 5  8 - Atualizo a linha do BG
        sta COLUBK              ; 3 11 - guardo o valor do BG no resitrador COLUPF

        lda (player0color),y ; 5 16 - Pega a cor do Player0 
        sta COLUP0              ; 3 19 - seta a cor do Player0 

        ; todo esse código acima precisa estar entre o ciclo 0 e 22
        ; para adicionar mais alguma coisa neste scanline, é preciso liberar algo acima
        ; sobraram apenas 3 ciclos ... é possível ainda colocar algum padrão de PF em PF1 e PF2

    ;--------------------------------------------------
    ; pre calcula os dados necessáriso para a segunda linha do 2LK
  
      ;  lda player1height      ; 2 21 - altura do Player0 - IMPORTANTE!! este valor deve ser altura-1
      ;  dcp player1y         ; 5 26 - Decrementa Player1Draw e compara com a altura
      ;  bcs DoDrawGrp1          ; 2 28 - (3 18) se o Carry estiver setado, player1 está na scanline atual
      ;  lda #0                  ; 2 31 - caso contrário, use 0 para desligar o player1
      ;  .byte $2C               ; 4 35 - $2C = BIT with absolute addressing, trick that
                                ;        causes the lda (BoxPtr),y to be skipped
DoDrawGrp1:                     ;   28 - 28 ciclos vindo do bcs DoDrawGRP1
      ;  lda (player1pointer),y      ; 5 32 - Carrega a aparencia do player1
        sta WSYNC               ; 3 35 - Aguarda o inicio de uma nova scanline

    ;---------------------------------------
    ; inicio da segunda linha do 2LK
      ;  sta GRP1                ; 3  3 - @0-22, desenha o player1 efetivamente (entre os ciclos 0 e 22)

      ;  lda (player1color),y ; 5  8 - Pega a cor do Player1 
      ;  sta COLUP1              ; 3 11 - seta a cor do Player1 

        ; todo o codigo acima precisa estar entre os ciclos 0 e 22.
        ; ainda há 11 ciclos sobrando, talvez um playfield ou ball, ou missile
        ; possa entrar aqui neste ponto.

        dey                     ; 2 13 - decrementa o y
        bne KernelLoop          ; 2 15 - se não for igual a zero, pula plá pra cima


;------------------------------------------------------------------------------
;------------------------------------------------------------------------------
;------------------------------------------------------------------------------


	sty COLUBK

custom_eat_visible
	;wait for the visible display to complete
	lda INTIM
	bne custom_eat_visible

custom_setup_overscan_timing
	        ifnconst overscan_time
        lda #35+128
        else
        lda #overscan_time+128-3-1
        endif
        sta TIM64T
        lda #%11000010
        sta WSYNC
        sta VBLANK

	;bB macro to return from a bank-switch gosub or from a regular gosub.
        RETURN


customPFPattern
    .byte %11011001
    .byte %11111111
    .byte %11011001
    .byte %11001001
    .byte %11011111
    .byte %11011001
    .byte %11011001
    .byte %11001001
    .byte %01001001
    .byte %01001001
    .byte %01001001
    .byte %01001001
    .byte %11001001
    .byte %00001000
    .byte %00001000
    .byte %11001001
    .byte %11011001

customPFColor:
    .byte $00, $AA, $00, $AA, $00, $AA, $00, $AA, $00, $AA, $00, $AA, $00

 

Thanks in advance.

 

 

Edited April 16, 2021 by Leonardo Santiago