diff --git a/Amiga-Graphics:-Fragments-of-Facts.md b/Amiga-Graphics:-Fragments-of-Facts.md index 9c562f1..e4d8767 100644 --- a/Amiga-Graphics:-Fragments-of-Facts.md +++ b/Amiga-Graphics:-Fragments-of-Facts.md @@ -1,9 +1,9 @@ Relative to the internal counters: -* NTSC: 262 lines, or 262/263 in interlaced mode; lines are alternately 227 and 228 cycles long; -* PAL: 312 lines, or 312/313 in interlaced mode; lines are 227 cycles long. +* NTSC: 262 lines, or 262/263 in interlaced mode; lines are alternately 227 and 228 slots long; +* PAL: 312 lines, or 312/313 in interlaced mode; lines are 227 slots long. -Each cycle being two processor clock ticks, or one NTSC-rate colour cycle — i.e. one chip RAM access window. +Each 'slot' being two processor clock ticks, or one NTSC-rate colour cycle — i.e. one chip RAM access window. Fixed slot per-line cycle access breakdown: @@ -18,9 +18,33 @@ Bitmap data fetch start time is programmable but may not begin earlier than slot ## DMA Priority -1. Bitplane fetching +1. Bitplane fetching (or disk/sprite/refresh, per line region) 2. Copper 3. Blitter 4. CPU -The Blitter will yield every fourth slot if BLTPRI in DMACON is clear. \ No newline at end of file +The Blitter will yield every fourth slot if BLTPRI in DMACON is clear. + +## Bitplane Fetches + +### Low-resolution + +An eight-slot fetch pattern is followed: + +1. [unused] +2. bit plane 4 +3. bit plane 6 +4. bit plane 2 +5. [unused] +6. bit plane 3 +7. bit plane 5 +8. bit plane 1 + +### High-resolution + +Four-slot fetch pattern: + +1. bit plane 4 +2. bit plane 2 +3. bit plane 3 +4. bit plane 1 \ No newline at end of file