127 lines
2.1 KiB
ArmAsm
127 lines
2.1 KiB
ArmAsm
// #LAYOUT# M65 KERNAL_1 #TAKE
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// #LAYOUT# * * #IGNORE
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// XXX deduplicate pointer manipulation
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M65_CLRSCR:
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// Clear additional attributes from the color code
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lda COLOR
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and #$0F
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sta COLOR
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// Disable the window mode
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lda #$00
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sta M64_SCRWINMODE
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// FALLTROUGH
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m65_clrscr_takeover:
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// Set the viewport to the beginning of screen memory - variables:
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// - M65_SCRVIEW, M65_COLVIEW
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// To clear the screen, two zeropage long pointers will be used, initialize them too
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// - M65_LPNT_SCR for screen memory
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// - M65_LPNT_KERN for colour memory (starts from $FF80000) // XXX preserve this on stack, restore afterwards
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sta M65_COLVIEW+0
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sta M65_COLVIEW+1
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sta M65_LPNT_KERN+0
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sta M65_LPNT_KERN+1
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lda #$F8
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sta M65_LPNT_KERN+2
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lda #$0F
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sta M65_LPNT_KERN+3
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lda M65_SCRSEG+0
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sta M65_SCRVIEW+0
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lda M65_SCRSEG+1
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sta M65_SCRVIEW+1
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lda M65_SCRBASE+0
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sta M65_LPNT_SCR+0
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lda M65_SCRBASE+1
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sta M65_LPNT_SCR+1
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lda M65_SCRSEG+0
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sta M65_LPNT_SCR+2
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lda M65_SCRSEG+1
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sta M65_LPNT_SCR+3
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// Clear the whole screen+color memory
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phz
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// FALLTROUGH
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m65_clrscr_loop:
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// Clear 80 characters
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ldz #$4F // 80 bytes
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!:
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lda #$20
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sta_lp (M65_LPNT_SCR),z
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lda COLOR
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sta_lp (M65_LPNT_KERN),z
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dez
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bpl !-
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// Move M65_LPNT_SCR and M65_LPNT_KERN 80 characters forward
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// XXX deduplicate with window clearing
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clc
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lda M65_LPNT_SCR+0
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adc #$50
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sta M65_LPNT_SCR+0
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bcc !+
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inc M65_LPNT_SCR+1
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!:
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clc
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lda M65_LPNT_KERN+0
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adc #$50
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sta M65_LPNT_KERN+0
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bcc !+
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inc M65_LPNT_KERN+1
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!:
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// Check if we have more rows to clear
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lda M65_LPNT_SCR+1
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cmp M65_SCRGUARD+1
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bne m65_clrscr_loop
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lda M65_LPNT_SCR+0
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cmp M65_SCRGUARD+0
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bne m65_clrscr_loop
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// Restore .Z register
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plz
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// Set screen+color base address in VIC IV
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// XXX deduplicate with mode setting routine
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lda #$00
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sta VIC_COLPTR+0
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sta VIC_COLPTR+1
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lda M65_SCRBASE+0
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sta VIC_SCRNPTR+0
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lda M65_SCRBASE+1
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sta VIC_SCRNPTR+1
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// Set screen variables
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// XXX provide proper implementation, together with HOME
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lda #$00
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sta M65__TXTROW
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sta M65__TXTCOL
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sta M65_TXTROW_OFF+0
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sta M65_TXTROW_OFF+1
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rts
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