7f56f90613
This was recomended by dicander and duunqnd because A =$ABAC looks like one address and not 2 zero-page addresses.
83 lines
1.6 KiB
ArmAsm
Executable file
83 lines
1.6 KiB
ArmAsm
Executable file
;;; -*- Mode: asm; indent-tabs-mode: t; tab-width: 8 -*-
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;;Screen print. Draws a pixel at a specified position.
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;; Destroys A X Y
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.proc pixel_draw; Draws a pixel at [Y = FB , X = FC, FD]. Y = 0 - 320, X= 0 - 200
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.include "mem.inc"
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Bitmap = $4000
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Bitmap_end = $5F3F
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;; X = X_pos (mod 8)
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LDA >X_pos ; X (mod 8)
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AND #%00000111
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TAX
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;;Store pixel in byte_to_paint
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LDA #%10000000
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INX
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@shift_btp: ;; check out SMB instruction here! //Hugo
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DEX
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BEQ end__;X=0 end this
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CLC
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ROR A
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jmp @shift_btp
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end__:
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STA byte_to_paint
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;;FIND THE POSITION IN MEMORY TO WRITE PIXEL
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;; + + + + + > X
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;; +
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;; +
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;;\/
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;; Y
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;;
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;;pos = x_offset
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LDA #%11111000
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AND >X_pos
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STA btp_mem_pos
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LDA <X_pos
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STA btp_mem_pos +1
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;;The y_pos adds offset because chunk offsets + inside chunk offset.
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;; Adding inside chunk offset
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LDA #%00000111 ; A = y (mod 8)
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AND Y_pos ;; offset to add
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TAY
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LDA #$00
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STA $4B
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;;y =8 translates to 320 bytes.
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CLC
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LDA #%11111000 ; A = y - [y (mod 8)]
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AND Y_pos
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STA C
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STA B
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LDA #$00
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STA C+1
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STA B+1
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;;We need to calculate C*40. 40 = 2*2*2*(2^2 +1)
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;; _*2^2
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Mult_16 C, C+1
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Mult_16 C, C+1
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;; + _*1
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Add_16 C, C+1, B, B+1, !
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;; *2*2*2
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Mult_16 C, C + 1
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Mult_16 C, C + 1
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Mult_16 C, C + 1
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Add_16 btp_mem_pos, btp_mem_pos + 1, C, C + 1, !
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;;add offset for where bitmap is
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Add_16 btp_mem_pos, btp_mem_pos + 1, #<Bitmap, #>Bitmap, !
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;;Let draw some stuff
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LDA byte_to_paint ;; note that both bytes are used!
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ORA (>btp_mem_pos), Y
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STA (>btp_mem_pos), Y
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RTS
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.endproc
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