65 lines
1.2 KiB
ArmAsm
65 lines
1.2 KiB
ArmAsm
// #LAYOUT# STD * #TAKE
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// #LAYOUT# * KERNAL_0 #TAKE
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// #LAYOUT# * * #IGNORE
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// Detect video system (PAL/NTSC), use method by Graham, as it is short and reliable
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// see here: https://codebase64.org/doku.php?id=base:detect_pal_ntsc
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setup_pal_ntsc:
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lda VIC_RASTER
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!:
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cmp VIC_RASTER
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beq !-
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bmi setup_pal_ntsc
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// Result in A, if no interrupt happened during the test:
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// #$37 -> 312 rasterlines, PAL, VIC 6569
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// #$06 -> 263 rasterlines, NTSC, VIC 6567R8
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// #$05 -> 262 rasterlines, NTSC, VIC 6567R56A
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cmp #$07
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bcc setup_ntsc
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// FALLTROUGH
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setup_pal:
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lda #$01
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skip_2_bytes_trash_nvz
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// FALLTROUGH
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setup_ntsc:
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lda #$00
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// FALLTROUGH
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setup_pal_ntsc_end:
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sta TVSFLG
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// FALLTROUGH
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setup_irq_timer: // entry point needed by UP9600 and CIA1 burst mod support
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// Sets up IRQ timer in CIA1 to ~1/60th of a second,
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// depending on the detected video system
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// Retrieve video system (0 - NTSC, 1 - PAL), assume PAL for unknown values
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ldx TVSFLG
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beq !+
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ldx #$01
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!:
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// Setup interval for timer A in CIA1
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lda irq_timing_lo, x
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sta CIA1_TIMALO // $DC04
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lda irq_timing_hi, x
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sta CIA1_TIMAHI // $DC05
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rts
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