ReadRegister returns the stored value of a register.

The display is drawn line-accurately: each scan line is rendered with the memory + ASIC state (mode, CLUT, border) as of the moment the beam passed it

Reset restores the paging state to the model's power-on defaults: port 7FFD = 0, port 1FFD = 0, port DFFD = 0, special paging disabled, page map back

Resolution returns the current resolution selector (0/1/2).

ResolvePage returns the physical 8K RAM page (0..) that a CPU read at addr currently maps to through the MMU / classic paging, or -1 if addr maps to R

SaveDisk serialises the disk in the given drive back to a file on host disk. Fails if no disk is currently mounted.

SaveMicrodrive writes the cartridge currently in drive `which` back to disk as a .mdr file. Returns an error if the drive is empty or the IF1 isn't en

Selected returns the currently-selected palette index (0..7).

SetAllReadHook installs a callback fired on EVERY Read (logical address + value), regardless of ROM/RAM/divMMC routing. Pass nil to remove. Used by --

SetByteLogger installs a per-byte callback fired on every SPI data byte clocked through the card. write=true means host -> card (WriteData), write=fal

SetIOBus attaches the port bus used for IO endpoints. Optional.

SetKempstonButton sets or clears a Kempston joystick button bit.

SetLogger installs a per-command callback for debugging. Pass nil to disable. The callback receives the 6-bit command index, the 32-bit argument, and

SetMicrodriveWriteProtect toggles the write-protect flag on the cartridge currently in drive `which`.

SetMultifaceActive pages the Next Multiface overlay in (true — done on the MF NMI, before it vectors to $0066) or out (false — done on RETN). The MF R

SetNextCopper installs the Spectrum Next Copper coprocessor. The compositor pass calls Step once per active scanline so MOVEs affecting palette / Laye

SetNextDAC installs the Spectrum Next four-channel DAC bank. Port writes are forwarded to it after the NextRegs / DMA priority checks; the bank intern

SetNextI2C installs the Spectrum Next i2c bus (RTC at $68). Ports $103B / $113B dispatch to it when present.

SetOverBorder sets NextReg $15 bit 1 ("sprites over border").

SetPagingTracer installs a per-write callback on the classic paging ports. Pass nil to disable.

SetPaletteOffset installs the NR$70 palette offset (bits 3:0).

SetPriority stores the 2-bit NR$44 priority (bits 1:0) for the entry.

SetRTC installs the RTC backing the M_GETDATE handler. When set, M_GETDATE returns the current host date packed into the guest's DE / HL / C registers

SetScrollX / SetScrollY set the tilemap pixel scroll offsets (NR$2F:$30 = X, 10-bit; NR$31 = Y, 8-bit per FPGA nr_30_tm_scrollx/nr_31). The tilemap wr

SetScrollY installs the 8-bit Layer 2 Y scroll (NR$17, layer2.vhd:156).

SetStubProtected toggles write-shadow protection on bank 1 offset $0009. When true, any guest write to that byte is silently dropped. Enable this when

SetTilemap attaches the tilemap layer (Layer 3). nil unhooks. Compositor uses the tilemap's "on_top" bit (NR$6B bit 0) to decide whether to paint it a

SortedKeys returns the PCs in the map in ascending numerical order. Used by both surfaces to render a stable list.

String returns the version with the product name, e.g. "zx_go v1.0 RC1".

SwitchModel changes the current Spectrum model and reconfigures memory

Sync flushes any buffered writes to stable storage. A no-op (nil) for read-only handles.

Transparency returns the currently-installed transparency index.

Tstates returns the T-state offset at which the active input block began recording. Used by the driver to seed CPU.tstates so memory contention timing

TypeRune injects the Spectrum SYMBOL-SHIFT combination for the typed character r (e.g. '.', ';', ':') as a brief overlay pulse, independent of the hos

WireDivMMCEntryPoints installs the NextReg $B8 / $BB handlers. These two registers gate which instruction-fetch PCs trigger the divMMC overlay paging-

WirePeripheral3 installs the NextReg $09 OnWrite handler. NextReg $09 is "Peripheral 3" per nextreg.txt; the only field with a side-effect outside the

WireTilemap installs the NextReg $6B / $6C / $6E / $6F OnWrite handlers that drive the Spectrum Next tilemap layer: $6B bit 7 enable, bit 6 mode (0=

Write writes buf to the file at the current cursor; for read-only or directory handles, returns an error.

WriteAddress latches the register selected for the next data write.

WriteDataPort writes one byte to the MDR data port. Every motor-on drive sees the write. Mirrors port_mdr_out at if1.c:803-839.

WriteSector overwrites the sector at (cyl, head, sector); fails if out of range or write-protected.

ZCTO returns the registered zero-count/timeout output (o_zc_to), asserted for one i_CLK cycle when the counter reaches zero (ctc_chan.vhd:183).

16-bit add with carry. Undocumented F3/F5 come from the HIGH byte of the result (bits 11 and 13), not the low byte.

16-bit arithmetic

Helper functions for IX operations

Helper functions for IY operations

allocCluster reserves a new cluster, sets its FAT entry to EOC, and returns the cluster number. Returns 0 if the disk is full.

applyKeepAliveDither adds a per-sample pseudo-random dither in [-amp, amp] to buf in place, advancing rng (a non-zero xorshift32 state). amp<=0 is a n

assertFilesEqual compares two parsed RZX files block-by-block. We don't use reflect.DeepEqual on the whole file because internal cursor state (current

bootNextToMenu cold-boots NextZXOS to its main menu, or skips the test if the Next ROMs / SD image are not installed (both are licensed, gitignored co

borderColourIndex extracts the 4-bit CLUT index from a BORDER value: low three bits plus bit 5 (mask 0x27).

buildRawSectorTrack wraps a flat block of sector bytes in a track byte stream using the supplied gap layout. Sector IDs start at baseSectorID and coun

--- tests ---------------------------------------------------------------

cmdGraph walks the History ring, filters entries by the supplied branch-source class, aggregates (caller → callee) edges, and returns the top-N most-f

cmdTraceNRDeltas arms a NextReg-transition tracer that logs ONLY writes that actually change the stored value (i.e. value-deltas). Distinct from `nr-t

--- FUSE-style per-cycle timing helpers --- These advance the T-state counter ONE machine cycle at a time and apply ULA memory contention at the cycl

countScreenPixels counts non-zero pixels in the screen area

cpuBank returns the 16K ROM bank currently mapped at $0000 on 128K-class machines. Mirrors cmd/zx_go/debugger.go's lookup so the cond.bank reference r

Helper to create plus2 and plus3 ROM files in addition to base ROMs

currentTstates returns the CPU's current T-state counter via the memory package's shared TStates pointer (set by the CPU at construction for memory co

defaultCrashConfig is what `--crash-detect` (with no per-heuristic flags) turns on. Conservative — pc-region and sp-high stay opt-in to avoid Next fal

divmmcFlagsFrom extracts the divMMC paging snapshot from a pager value via the same duck-typed interfaces get-divmmc uses. conmem is E3 bit 7. A nil p

Per-access memory contention for the ED block opcodes (LDI/LDD/LDIR/LDDR, CPI/CPD/CPIR/CPDR, INI/IND/INIR/INDR, OUTI/OUTD/OTIR/OTDR). The block memory

effectiveJoystick is effectiveJoystickFor applied to the live model.

emitFiller writes n copies of the gap filler byte. No clock marks set.

ensureFileExt appends ext to path (and renames the file on disk) when path doesn't already end in ext, case-insensitively. Used by the save dialogs so

findSignEnd returns the file's sign-end block payload, or nil.

flushRaster renders up to the current raster position; the video-write hook and display-affecting OUTs call it before mutating state.

--- helpers ---

generateSquareWaveFrame is the box-filter square-wave reconstruction shared by the beeper and the tape-loading sound: it integrates a 1-bit signal (to

importAndRunNex copies data onto the SD card and starts the loader macro. It runs on its own goroutine (the SD write can be large) with the emulator p

initialDataCRC returns the CRC accumulator state after the implied 3×A1 sync prefix and the data address mark (FB for normal data, F8 for deleted), ma

listSymbols returns every (addr, name) pair sorted by address. Used by the `sym` (no-arg) debugger command.

loadSZXRamPage loads a RAM page from SZX block

loadSZXZ80Regs loads Z80 CPU registers from SZX block

loadTapeFile mounts a .tap/.tzx tape image into the emulator's ULA tape player and starts it playing — the headless-mode equivalent of the GUI's "Open

lookupPhys returns the last-writer record for a physical pool cell.

memReader builds a readFunc from a sparse map of byte values. Anything not in the map reads as 0x00.

mixInt16 adds src into dst element-wise with int16 saturation. Used to fold the DAC frame into the beeper frame without wrap-around pops.

newAudioTestULA returns a bare ULA struct suitable for the audio generator tests. It has no real memory or audio system attached; the tests only use t

nexPressCombo presses a set of matrix keys together, holds, releases, then pauses — long enough for the NextZXOS 50 Hz key scan to register a distinct

nextTestROMs lays down the minimal ROM blobs memory.New(ModelNext) needs, so the test is self-contained (no dependency on the repo's roms/ tree or its

nr02NMIHarness wires a dispatcher + memory + CPU and returns both the dispatcher and the CPU so tests can observe PendingNMI.