Super Mario Bros. graphics and sound (doppelganger's SMBDIS via Xkeeper0/smb1)

Each frame the NMI handler waits for the sprite 0 flag to clear, spins until the sprite 0 hit, waits a short loop for horizontal blank, and only then writes the level's scroll, so the status bar above the hit stays still. smb1-av/sprite-0-split

About: Super Mario Bros. Status bar split

Cited by: Status bar split

The game sets sprite 0 to OAM bytes $18, $FF, $23, $58, so tile $FF sits at Y $18 and X $58 behind the background in sprite palette 3. smb1-av/sprite-0-placement

About: Super Mario Bros. Status bar split

{
 "y": 24,
 "tile": 255,
 "attributes": 35,
 "x": 88
}

The OAM bytes are Y, tile, attributes, X (nesdev-ppu-oam). Attribute $23 sets bit 5 (behind the background) and palette bits 3. Which status-bar tile the hit lands on was not checked; a probe should name it.

Cited by: Status bar split

Every unpaused frame SpriteShuffler adds one of three amounts, $58, $48, or $38 in turn, to each object's OAM offset at or above $28, wrapping within $28-$FF, so the objects' sprites change OAM slots each frame and a ninth sprite on a line drops out on different frames. smb1-av/sprite-shuffle

About: Super Mario Bros. Sprite flicker

{
 "amounts": [
  88,
  72,
  56
 ],
 "floor": 40,
 "phases": 3
}

The claim that a dropped sprite moves between frames follows from the PPU's in-order search (nesdev-ppu-oam); the atlas has not measured which sprites flicker in play.

Cited by: Sprite flicker

Every 8th frame ColorRotation rewrites background palette 3 at $3F0C, putting the next of six colors, $27, $27, $27, $17, $07, $17, in its second entry, so the question blocks and coins shimmer on a 48-frame loop. smb1-av/color-rotation

About: Super Mario Bros. Palette cycling

{
 "palette": "$3F0C",
 "entry": 1,
 "colors": [
  39,
  39,
  39,
  23,
  7,
  23
 ],
 "framesPerStep": 8,
 "loopFrames": 48
}

BlankPalette is a VRAM buffer header (address $3F0C, 4 bytes); the area-type row of Palette3Data fills it and the cycled color overwrites entry 1. Which tiles use palette 3 is a T0 reading from play, not checked in the level data.

Cited by: CHR bank switching, Palette cycling

The cartridge header declares two 16 KB PRG ROM pages and one 8 KB CHR ROM page, so the game's tile set never changes. smb1-av/chr-fixed

About: Super Mario Bros. CHR bank switching

{
 "prgPages": 2,
 "chrPages": 1,
 "chrKB": 8
}

Byte 6 = 1 with byte 7 = 0 is mapper 0 (NROM) with vertical mirroring in the iNES format; the atlas has no pinned iNES reference yet, so the mapper number rests on that reading.

Cited by: Super Mario Bros.

The NMI handler calls the sound engine once a frame; its music handler steps square 2, square 1, the triangle, and the noise channel in turn, and each channel counts its note length down by 1 per frame and reads its next byte at 0. smb1-av/music-loop

About: Super Mario Bros. Music driver

{
 "order": [
  "square2",
  "square1",
  "triangle",
  "noise"
 ],
 "tick": "frame"
}

Cited by: Music driver

A song's header picks an 8-entry row of MusicLengthLookupTbl, and a length code of 0-7 indexes it in frames; the overworld theme's row is 54, 3, 9, 6, 18, 27, 36, 12, a quarter note of 18 frames, and the hurry-up version adds 8 to the row offset for 36, 2, 6, 4, 12, 18, 24, 8. smb1-av/note-lengths

About: Super Mario Bros. Music driver

{
 "overworld": [
  54,
  3,
  9,
  6,
  18,
  27,
  36,
  12
 ],
 "hurry": [
  36,
  2,
  6,
  4,
  12,
  18,
  24,
  8
 ],
 "table": [
  5,
  10,
  20,
  40,
  80,
  30,
  60,
  2,
  4,
  8,
  16,
  32,
  64,
  24,
  48,
  12,
  3,
  6,
  12,
  24,
  48,
  18,
  36,
  8,
  54,
  3,
  9,
  6,
  18,
  27,
  36,
  12,
  36,
  2,
  6,
  4,
  12,
  18,
  24,
  8,
  18,
  1,
  3,
  2,
  6,
  9,
  12,
  4
 ]
}

Every overworld part's header starts with $18. Reading 18 frames as a quarter note gives about 200 beats a minute at 60.1 frames a second; the note-value reading is the atlas's, not the disassembly's.

Cited by: Music driver

A note byte is an offset into FreqRegLookupTbl, a table of 51 two-byte timer periods that the driver writes to the channel's timer registers; a recreation turns period $t$ into $f_{CPU}/(16(t+1))$ Hz on a square channel and half that on the triangle. smb1-av/period-table

About: Super Mario Bros. Music driver

[
 136,
 47,
 0,
 678,
 640,
 604,
 570,
 538,
 479,
 452,
 427,
 403,
 380,
 359,
 339,
 320,
 302,
 285,
 269,
 254,
 239,
 226,
 213,
 201,
 190,
 179,
 169,
 160,
 151,
 142,
 134,
 119,
 126,
 113,
 84,
 100,
 95,
 89,
 80,
 71,
 67,
 59,
 53,
 42,
 35,
 1141,
 855,
 761,
 719,
 508,
 106
]

Pairs are stored high byte first. Period 254 gives 438.7 Hz on a square channel and 508 gives 219.8 Hz, so the table sits close to A = 440 Hz equal temperament.

Cited by: Music driver

A new area-music square note sets duty and volume byte $82 and an envelope index of 8; each frame the driver writes AreaMusicEnvData[index] to the channel and counts the index down, so the note plays at 50% duty with volumes 0, 8, 7, 6, 5, 5, 4, 4 and then 0 until the next note. smb1-av/square-envelope

About: Super Mario Bros. Music driver

{
 "duty": 0.5,
 "volumes": [
  0,
  8,
  7,
  6,
  5,
  5,
  4,
  4,
  0
 ],
 "table": [
  144,
  148,
  148,
  149,
  149,
  150,
  151,
  152
 ]
}

On the note's first frame the index is still 8 when it is read (the DEC is to memory, after LDY), so it reads one byte past the 8-byte table, the first byte of WaterEventMusEnvData, $90: volume 0 for one frame. Bits 7-6 of $9x are duty 2 (50%) and bit 4 is constant volume (nesdev-apu-pulse). Water music uses WaterEventMusEnvData and an index of $28 instead. A Mesen probe of $4004 would confirm the per-frame trace.

Cited by: Music driver

The noise channel plays three drum sounds, all at constant volume 12 ($400C = $1C), a short beat at period index 3, a strong beat at period index 12, and a long beat at period index 3 with a longer length-counter load ($58 instead of $18). smb1-av/noise-beats

About: Super Mario Bros. Music driver

{
 "short": [
  28,
  3,
  24
 ],
 "strong": [
  28,
  12,
  24
 ],
 "long": [
  28,
  3,
  88
 ],
 "silent": [
  16
 ]
}

Period indexes 3 and 12 are 32 and 762 CPU cycles on NTSC (nes-hardware/noise). The underground and castle songs skip the noise routine.

Cited by: Music driver

During the overworld and underwater songs the sound engine raises a counter by 1 a frame up to $30 and writes it to the DMC's output level at $4011; other songs count it back down to 0, and the game plays no samples. smb1-av/dac-level

About: Super Mario Bros. DPCM samples

{
 "max": 48,
 "step": 1
}

Area music bits 0 and 1 are the ground and water songs (AreaMusicBuffer). The audible effect of the raised level on the other channels is not sourced here; the NESdev APU Mixer page would be the anchor. "No samples": the disassembly never writes the sample address or length registers ($4012, $4013); its only other DMC write resets $4011 at power-on (src/prg.asm line 31).

Cited by: DPCM samples