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126 lines
3.5 KiB
ArmAsm
126 lines
3.5 KiB
ArmAsm
;
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; 1998-08-06, Ullrich von Bassewitz
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; 2020-10-09, Greg King
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;
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; void cputcxy (unsigned char x, unsigned char y, char c);
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; void cputc (char c);
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;
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.export _cputcxy, _cputc, cputdirect, putchar
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.export newline, plot
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.import gotoxy
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.import PLOT
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.scope KERNAL
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.include "cbm_kernal.inc"
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.endscope
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.include "vic20.inc"
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; VIC-20 KERNAL routines (such as PLOT) do not always leave the color RAM
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; pointer CRAM_PTR pointing at the color RAM location matching the screen
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; RAM pointer SCREEN_PTR. Instead they update it when they need it to be
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; correct by calling UPDCRAMPTR.
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;
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; We make things more efficient by having conio always update CRAM_PTR when
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; we move the screen pointer to avoid extra calls to ensure it's updated
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; before doing screen output. (Among other things, We replace the ROM
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; version of PLOT with our own in libsrc/vic20/kplot.s to ensure this
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; precondition.)
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;
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; However, this means that CRAM_PTR may be (and is, after a cold boot)
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; incorrect for us at program startup, causing cputc() not to work. We fix
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; this with a constructor that ensures CRAM_PTR matches SCREEN_PTR.
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;
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UPDCRAMPTR := KERNAL::UPDCRAMPTR ; .constructor doesn't understand namespaces
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.constructor UPDCRAMPTR
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_cputcxy:
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pha ; Save C
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jsr gotoxy ; Set cursor, drop x and y
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pla ; Restore C
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; Plot a character -- also used as an internal function
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_cputc: cmp #$0D ; Is it CBM '\n'?
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beq newline ; Recalculate pointers
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cmp #$0A ; Is it CBM '\r'?
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beq cr
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; Printable char. of some sort
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; Convert it from PetSCII into a screen-code
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cmp #$FF ; BASIC token?
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bne convert
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lda #$DE ; Pi symbol
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convert:
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tay
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lsr a ; Divide by 256/8
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lsr a
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lsr a
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lsr a
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lsr a
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tax ; .X = %00000xxx
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tya
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eor pet_to_screen,x
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cputdirect:
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jsr putchar ; Write the character to the screen
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; Advance the cursor position
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advance:
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iny
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cpy #XSIZE
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bne L3
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jsr newline ; Wrap around
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cr: ldy #$00 ; Do carriage-return
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L3: sty CURS_X
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rts
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; Move down by one full screen-line. Note: this routine doesn't scroll.
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;
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; (Both screen RAM and color RAM are aligned to page boundaries.
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; Therefore, the lower bytes of their addresses have the same values.
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; Shorten the code by taking advantage of that fact.)
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newline:
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clc
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lda #XSIZE
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adc SCREEN_PTR
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sta SCREEN_PTR
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sta CRAM_PTR
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bcc L5
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inc SCREEN_PTR+1
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inc CRAM_PTR+1
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L5: inc CURS_Y
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rts
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; Set cursor position, calculate RAM pointers
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plot: ldy CURS_X
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ldx CURS_Y
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clc
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jmp PLOT ; Set the new cursor
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; Write one character to the screen without doing anything else,
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; return the X position in .Y
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putchar:
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ora RVS ; Set revers bit
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ldy CURS_X
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sta (SCREEN_PTR),y ; Set char.
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lda CHARCOLOR
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sta (CRAM_PTR),y ; Set color
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rts
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.rodata
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pet_to_screen:
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.byte %10000000,%00000000,%01000000,%00100000 ; PetSCII -> screen-code
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.byte %01000000,%11000000,%10000000,%10000000
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