Struct Action53M28 

pub struct Action53M28 { /* private fields */ }

Mapper 28 (Action 53 homebrew multicart).

Implemented from the NESdev wiki “Action 53 mapper” page (vendored at nesdev_wiki/output/Action_53_mapper.md) and pinned to Damian Yerrick’s test28 ROM (tests/roms/nes-test-roms/other/test28.nes).

Four registers are selected through $5000-$5FFF (bit 7 = supervisor, bit 0 = register) and written through $8000-$FFFF, with no bus conflicts:

• $00 CHR bank: bits 0-1 pick one of four 8 KiB banks of the 32 KiB CHR RAM.
• $01 inner PRG bank: bits 0-3.
• $80 mode: bits 0-1 mirroring (0/1 = 1-screen lower/upper, 2 = vertical, 3 = horizontal), bits 2-3 PRG mode, bits 4-5 outer bank size (32/64/128/256 KiB).
• $81 outer PRG bank: all 8 bits.

While mirroring is 1-screen, D4 of a write to $00 or $01 replaces mirroring bit 0 (AxROM’s single-screen select); in V/H it is ignored.

PRG resolution follows the wiki’s 12-row table: the “o” bits of the 16 KiB bank number come from the top of the outer register and the “i” bits from the bottom of the inner register, the number of inner bits growing with the outer bank size. The fixed half of the UNROM-style modes ($8000 in mode 2, $C000 in mode 3) is resolved as if the size were 32 KiB, so all outer bits pass straight through. Power-on maps the last 16 KiB at $C000; reset leaves the mapper untouched.

Until v2.9.3 this board shifted the outer bank left instead of masking its low bits, masked the inner bank to one bit, fixed the wrong half in modes 2 and 3, ignored the CHR bank register and the D4 mirroring write, and powered on at bank 1 in $C000 – so test28 failed its first check. The review thread on #97 reported the banking half.

Implementations

impl Action53M28

pub fn new( prg_rom: Box<[u8]>, _chr_rom: &[u8], _mirroring: Mirroring, ) -> Result<Self, MapperError>

Construct a new mapper 28 board.

Errors

Returns MapperError::Invalid when PRG is not a non-zero multiple of 16 KiB.

Trait Implementations

impl Mapper for Action53M28

fn caps(&self) -> MapperCaps

v2.8.0 Phase 4 — the mapper’s per-CPU-cycle capability flags.

fn cpu_read(&mut self, addr: u16) -> u8

Read a byte from the CPU address space $4020-$FFFF.

fn cpu_write(&mut self, addr: u16, value: u8)

Write a byte to the CPU address space $4020-$FFFF.

fn ppu_read(&mut self, addr: u16) -> u8

Read a byte from the PPU address space $0000-$3FFF (pattern table

fn ppu_write(&mut self, addr: u16, value: u8)

Write a byte to the PPU address space $0000-$3FFF.

fn current_mirroring(&self) -> Mirroring

Returns the mapper’s current effective mirroring layout.

fn save_state(&self) -> Vec<u8>

Encode the mapper’s mutable state into a tagged save-state blob.

fn load_state(&mut self, data: &[u8]) -> Result<(), MapperError>

Decode a previously Mapper::save_state blob back into the mapper.

fn cpu_read_unmapped(&self, addr: u16) -> bool

Returns true when addr is not wired to mapper-resident memory — i.e. when cpu_read(addr) returns junk and the bus should fall through to the open-bus latch instead of overwriting it. The CPU databus is left floating in this case, so the most recently driven byte stays visible to the next read.

fn notify_floating_read(&mut self, _addr: u16, _value: u8)

A CPU read the mapper declined (Self::cpu_read_unmapped) has just completed, and value is what floated on the bus.

fn notify_ppu_register_write(&mut self, _addr: u16, _value: u8)

The CPU wrote value to the PPU register window ($2000-$3FFF), at the undecoded address addr.

fn nametable_unfolded(&self) -> bool

Whether PPU $3000-$3EFF is independent RAM on this cartridge rather than a mirror of $2000-$2EFF.

fn cpu_read_driven_mask(&self, _addr: u16) -> u8

Which data bits a mapped read in the register window ($4020-$5FFF) actually drives; the rest float and keep the bus’s open-bus value.

fn ppu_read_sprite(&mut self, addr: u16) -> u8

Read a byte from the PPU pattern-table window ($0000-$1FFF) on behalf of a sprite tile fetch. MMC5 in 8x16 sprite mode uses a separate set of CHR bank registers ($5120-$5127) for sprite fetches; other mappers default to forwarding to Mapper::ppu_read.

fn chr_phys(&self, _addr: u16) -> Option<u32>

HD-pack tile identity: the ABSOLUTE post-banking offset into CHR-ROM for a pattern-space address $0000-$1FFF (Some(offset)), or None for CHR-RAM (content-hashed instead). tile_index = offset / 16 is the key Mesen uses for CHR-ROM <tile> replacements. Default None so an unported mapper falls back to the content-hash path (no worse than before); the common CHR-ROM mappers override it by exposing their internal CHR mapping.

fn chr_reads_are_pure(&self) -> bool

v3.1.0 (T-SPRITE-LIMIT) — whether Self::ppu_read and Self::ppu_read_sprite on $0000-$1FFF change nothing but return a byte. true (the default) lets the PPU’s “disable sprite limit” option make extra, display-only pattern reads on this board.

fn set_mmc3_revision_override( &mut self, _revision: Option<Mmc3Revision>, ) -> bool

v3.1.0 (T-MMC3-NEC-OVERRIDE, ACC-13) — force an MMC3’s IRQ revision (Some), or return to the one its header selected (None). Returns whether this board is an MMC3 that applied it; every other board ignores it (the default). Lets an iNES 1.0 dump, which cannot name its MMC3 revision, run under the alternate (Nec) behaviour.

fn nametable_fetch(&mut self, _addr: u16) -> Option<u8>

Optionally synthesize a nametable byte for addr ($2000-$3EFF).

fn nametable_write(&mut self, _addr: u16, _value: u8) -> bool

Optionally absorb a nametable write for addr ($2000-$3EFF) directly into mapper-resident storage.

fn peek_ex_attribute(&mut self, _v: u16) -> Option<ExAttribute>

Optionally provide per-tile extended attribute + CHR-bank override for the BG tile currently being fetched.

fn bg_split_state( &mut self, _scanline_y: u16, _coarse_x: u16, ) -> Option<BgSplitState>

Optionally redirect a BG fetch group into a vertical split-screen “alt region”.

fn nametable_address(&self, addr: u16) -> u16

Resolve a nametable address in $2000-$3EFF to a CIRAM offset in 0..0x800. The PPU owns the 2 KiB CIRAM and uses this hook to apply per-mapper mirroring without giving the mapper direct access to the console-side VRAM.

fn notify_a12(&mut self, _level: bool)

Notify of a PPU A12 line transition. Default no-op; MMC3 / MMC5 override this for IRQ counter clocking.

fn notify_a12_at_sub_dot(&mut self, level: bool, _sub_dot: u8)

Notify of a PPU A12 line transition with the current sub-dot of the host CPU cycle (0 / 1 = M2-low half; 2 = M2-high half). Default impl falls through to Self::notify_a12 so existing mappers compile unchanged; MMC3 overrides this for the M2-phase-aware IRQ-output propagation delay required by mmc3_test_2/4-scanline_timing sub-test #3 (C1 step B4 successor).

fn notify_cpu_cycle(&mut self)

Notify of a CPU cycle. Default no-op; VRC2/4/6, FME-7, Namco 163 override this for IRQ counter clocking.

fn reset(&mut self)

The console’s RESET button (a soft reset, not a power cycle).

fn notify_frame_event(&mut self, _events: MapperFrameEvents)

Notify the mapper of the APU frame-counter events fired on the current CPU cycle (quarter-frame envelope clock, half-frame length clock). Only on-cart audio extensions that re-use the 2A03 frame counter cadence need to handle this (MMC5 audio’s two pulse channels). Default no-op.

fn notify_scanline_start(&mut self)

Notify the mapper that the PPU is starting a new rendered scanline.

fn notify_vblank(&mut self)

Notify the mapper that the PPU has entered vertical blank.

fn enable_vs_dual_wram(&mut self)

v2.0.0 beta.5 (Vs. DualSystem): provision the board’s shared 2 KiB work RAM at $6000-$7FFF (mirrored across the 8 KiB window — MAME vsnes.cpp: map(0x6000, 0x67ff).mirror(0x1800).ram()). Only the Vs. System board (mapper 99) implements this — the DualSystem cabinets carry a 2 KiB RAM shared between the two consoles, absent on UniSystem carts (whose $6000 window stays open bus, byte-identically). Called by the VsDualSystem wrapper at construction on both consoles: each console holds its own COPY, and the wrapper converges the copies by draining the write log (below) after every stepped instruction — MAME’s fully-shared .share("nvram") model at soft-lockstep granularity. Default no-op.

fn set_vs_dual_sub(&mut self)

v2.0.0 beta.5 (Vs. DualSystem): mark this mapper instance as the cabinet’s SUB console — it banks the second 32 KiB PRG half and the upper CHR pages (the two CPUs run DIFFERENT programs; MAME balonfgt loads distinct sub-region ROMs, Mesen2 uses prgOuter = IsVsMainConsole() ? 0 : 4). Applied by the VsDualSystem wrapper at construction, like the bus’s sub identity. Default no-op.

fn drain_vs_dual_wram_writes(&mut self, dst: &mut Vec<(u16, u8)>)

v2.0.0 beta.5 (Vs. DualSystem): drain this console’s shared-WRAM write log — every (offset, value) the CPU wrote to the window since the last drain, in order — by APPENDING into dst (never clearing it first). The wrapper replays them into the partner’s copy (Self::apply_vs_dual_wram_write), which is what makes the RAM behave as ONE simultaneously-shared memory (MAME’s model; nesdev also documents a $4016-bit-1 access mux, but MAME — where the four DualSystem games verifiably run — shares the RAM unconditionally, and Balloon Fight’s boot handshake requires the partner to see writes made while the mux would deny it access).

fn take_vs_dual_wram_writes(&mut self) -> Vec<(u16, u8)>

Convenience wrapper around Self::drain_vs_dual_wram_writes for callers that don’t already hold a reusable buffer (diagnostics, tests) — NOT used by the hot pump_comms path, which owns and reuses its own scratch buffer instead.

fn apply_vs_dual_wram_write(&mut self, offset: u16, value: u8)

v2.0.0 beta.5 (Vs. DualSystem): replay one partner-console write into this console’s copy of the shared WRAM (see Self::take_vs_dual_wram_writes). Does NOT re-log the write (no echo loop). Default no-op.

fn take_vs_dual_wram(&mut self) -> Option<Box<[u8]>>

v2.0.0 beta.5 (Vs. DualSystem): take the console’s shared-WRAM copy (used by the wrapper’s snapshot-restore normalization — the two copies are re-converged from one buffer after a restore). Returns None on boards without the dual WRAM. Default None.

fn set_vs_dual_wram(&mut self, wram: Box<[u8]>)

v2.0.0 beta.5 (Vs. DualSystem): install a shared-WRAM copy (the other half of the restore normalization). Default no-op.

fn irq_pending(&self) -> bool

Returns true if the mapper is currently asserting an IRQ.

fn irq_acknowledge(&mut self)

Acknowledge a pending IRQ. Default no-op; mappers that latch IRQ state override this.

fn mix_audio(&mut self) -> i32

Return one signed audio sample for mappers with on-cart audio (VRC6/7, MMC5, Sunsoft 5B, Namco 163, FDS). Default returns silence.

fn has_hardwired_mirroring(&self) -> bool

Whether this mapper’s nametable mirroring is hardwired by the cartridge (solder pads / the iNES header bit) rather than controlled by the mapper’s own registers at runtime.

fn disk_side_count(&self) -> usize

Number of disk sides in the inserted image (0 for non-FDS mappers).

fn inserted_disk_side(&self) -> Option<usize>

The currently inserted disk side index, or None when ejected (or for non-FDS mappers).

fn set_disk_side(&mut self, _side: Option<usize>)

Insert disk side i (Some) or eject the disk (None). No-op for non-FDS mappers; an out-of-range index is ignored by the FDS device.

fn sram(&self) -> &[u8]

Returns a reference to the mapper’s internal SRAM/PRG-RAM. By default, returns an empty slice if unsupported.

fn sram_mut(&mut self) -> &mut [u8]

Returns a mutable reference to the mapper’s internal SRAM/PRG-RAM. By default, returns an empty mutable slice if unsupported.

fn save_data(&self) -> &[u8]

The cartridge’s non-volatile data: what a battery save persists and a power cycle keeps. For almost every board that is its battery-backed RAM, Self::sram, and the default says so.

fn save_data_mut(&mut self) -> &mut [u8]

Mutable Self::save_data, for loading a save.

fn clear_save_data(&mut self)

Return the save data to the state of a cartridge that has never been saved to. That is zeroed RAM by default. On a flash board it is the PRG image as loaded, since a zero-filled flash would be a ROM with no program in it. A power-on movie calls this (power_on_for_movie).

fn enable_fds_trace(&mut self)

Start recording the diagnostic FDS read-stream trace (off by default; observation-only). No-op for non-FDS mappers. See crate::FdsTraceRec.

fn take_fds_trace(&mut self) -> Vec<FdsTraceRec>

Drain the accumulated FDS read-stream trace records (empty for non-FDS mappers / when tracing was never enabled).

fn disk_image_bytes(&self) -> Vec<u8>

Re-serialize the (possibly-modified) disk image to its byte layout for host persistence. Returns an empty vector for non-FDS mappers.

fn disk_is_dirty(&self) -> bool

Whether the disk image has unsaved writes. Always false for non-FDS mappers.

fn clear_disk_dirty(&mut self)

Clear the disk dirty flag (a host calls this after persisting). No-op for non-FDS mappers.

fn set_disk_write_protected(&mut self, _protected: bool)

Mark the inserted disk read-only (true) or writable (false). No-op for non-FDS mappers.

fn nsf_song_count(&self) -> u8

Number of selectable songs (0 for a non-NSF mapper).

fn nsf_current_song(&self) -> u8

The currently-selected 0-based song (0 for a non-NSF mapper).

fn nsf_set_song(&mut self, _song: u8) -> bool

Select a 0-based song. Returns true if this is an NSF mapper (so the caller knows to re-run the reset that re-vectors into the driver’s init). Default no-op returning false.

fn debug_info(&self) -> MapperDebugInfo

Surface read-only debug info for the UI. Override per mapper to expose bank registers, IRQ counters, etc. Default returns a minimal entry naming the mapper id.