Skip to article frontmatterSkip to article content
Site not loading correctly?

This may be due to an incorrect BASE_URL configuration. See the MyST Documentation for reference.

Peripherals and expansion

Zorro autoconfig (zorro.rs)

The ZorroChain implements the Zorro II/III autoconfig protocol -- nibble-encoded config ROMs in the $E80000 window, base-address assignment, shut-up, chain advance, and power-on reset. Boards are described by data (BoardSpec) rather than a trait; the built-in fast and Z3 RAM options and user [[zorro]] metadata boards all build the same specs. The user-facing guide, including the metadata file format and the autoconfig walk-through, is Writing Zorro board plugins.

Fat Gary and Ramsey (gary.rs, ramsey.rs)

The A3000 and A4000 profiles fit the big-box motherboard pair: Fat Gary, the bus controller, and Ramsey, the memory controller. Both answer in the $DE0000 page Gary decodes, with an address decode cruder than a register map suggests: only the byte lane and two address bits matter (lanes 0-2 are Gary’s, lane 3 is Ramsey’s), and the whole layout repeats every $100 to the end of the page, so every register is mirrored many times over -- the Ramsey version register Kickstart reads at $DE0043 answers equally at $DE0047 or $DE0143. Diagnostic tools reading addresses that look like nothing in particular are reading a mirror.

Gary’s three registers are single read/write bits in bit 7: TIMEOUT ($DE0000, whether an unanswered bus cycle produces BERR or DSACK), TOENB ($DE0001, timeout enable), and COLDBOOT ($DE0002, the power-up flag the OS clears on warm reboot). None of them change emulated behaviour -- bus timeouts are not modelled; an unanswered cycle floats -- but the read/write COLDBOOT bit is what identification tools use to detect a Fat Gary, and without one they never go looking for the Ramsey behind it.

Ramsey drives the motherboard fast RAM ([memory] motherboard): a 32-bit local bank ending at $08000000 and growing downward, so a full 16 MiB reaches $07000000. Its two byte-wide registers sit on lane 3: the control register at $DE0003 (refresh rate, page/burst/skip modes, DRAM geometry) and the read-only version register at $DE0043 -- $0D for the A3000’s Ramsey-04, $0F for the A4000’s Ramsey-07, a distinction that matters because the two parts disagree about control bit 4 (Ramsey-04 DRAM width versus Ramsey-07 cycle-skip mode). Refresh and the speed modes have no observable effect in an emulator that never loses a DRAM cell, but the bits store and read back because Kickstart and the diagnostic tools write a mode and spin until they read it back, and the geometry bits are seeded to describe DRAM parts matching the fitted RAM size so sizing probes agree with the RAM that answers. Only the register file lives in ramsey.rs; the RAM bank itself is memory::Memory::mb_ram.

Beyond Ramsey’s four banks the big-box memory map reserves $04000000-$06FFFFFF for motherboard RAM expansion; on the A4000 profile the bank keeps growing downward through it, up to 64 MiB at $04000000, still sized by Kickstart’s top-down probe (the control register keeps describing the fully populated 1Mx4 geometry -- it has no way to say more). The complementary [memory] accelerator bank models CPU-slot local RAM: it starts at $08000000 and grows upward through the coprocessor-slot space, up to 128 MiB at $10000000 where Zorro III space begins, gated only on a 32-bit CPU (memory::Memory::accel_ram).

Gayle IDE (gayle.rs)

A600/A1200 machines get the Gayle gate array: the ID register at $DE1000, the IDE task file at $DA0000 (byte registers on the odd word half, 4-byte stride), and the IDE interrupt and status bits. Drives are raw flat HDF images with an RDB inside, opened read/write; PIO transfers complete synchronously within the access. One hardware subtlety worth knowing: Gayle byte-swaps the IDE bus, so IDENTIFY data words are low-byte-first while sector data passes through untouched -- Kickstart 3.1 expects exactly this. The absent-slave behaviour follows the WinUAE-verified model so device scans terminate correctly. PCMCIA reports an empty slot (the status/config registers exist so card.resource behaves); credit-card device emulation is a non-goal.

Either drive slot may instead be an ATAPI CD-ROM (a .cue/.iso/.chd image): ata.rs’s task-file engine drives the PACKET (0xA0) command, handing 12-byte CDBs to the same bus-agnostic SCSI-2 CD-ROM command engine (scsi/cd.rs’s ScsiCdRom) the [scsi] host adapters use, so the read family, TOC/sub-channel queries, mode pages, and CD-DA playback all behave identically over ATAPI PACKET or a WD33C93 SCSI bus.

A4000 motherboard IDE (ide_a4000.rs)

The A4000 profile decodes the same ATA task file (ata.rs) at $DD2020 with no gate array in front of it -- the layout Kickstart’s own scsi.device probes, with the Gayle-style 4-byte register stride, the control block one A12 page up at $DD3038, and an interrupt status byte at $DD3020 whose bit 7 is the drive’s INTRQ. Unlike Gayle there is no interrupt-change latch: INTRQ feeds INT2 directly and the driver drops it by reading the status register. Drives come from the same [ide] section as Gayle machines, ATAPI CD-ROMs included -- same ata.rs engine, same PACKET protocol.

SCSI controllers (a2091.rs, a4091.rs, sdmac.rs, scsi.rs)

The [scsi] option attaches one of three host adapters, selected by its controller key: the Zorro II A2091 (the default), the Zorro III A4091, or the A3000’s motherboard Super DMAC. All three drive the same SCSI-2 target layer in scsi.rs.

A2091 (a2091.rs)

The A2091 is a Zorro II device board pairing the Commodore DMAC (rev 02 modeled) with a WD33C93A SBIC, plus the board’s autoboot ROM whose scsi.device drives them. The autoconfig identity comes from the DMAC -- Commodore West Chester (514), product 3, ERTF_DIAGVALID with er_InitDiagVec pointing at $2000 -- while the ROM supplies the DiagArea and the driver; the ROM image therefore is a required configuration input (rom/rom_odd, split even/odd EPROM dumps interleaved U13-first).

Board window layout: ISTR $40, CNTR $42, WTC $80/$82, ACR $84/$86 (low bit forced even), DAWR $8E, the WD33C93 SASR/auxiliary status at $90/$91 and data port at $92/$93, the ST_DMA/SP_DMA/CINT/ FLUSH strobes at $E0/$E2/$E4/$E8 (read- or write-triggered), and the boot ROM repeating from $2000 to the end of the 64K window. Unpopulated decode below the ROM reads as floating bus ($FF): the boot ROM’s drive probe ANDs the A590 XT-interface bytes at $A1/$A3/$A5/$A7 and only takes the SCSI-only path when they all read $FF -- zeros wedge it polling a phantom XT drive.

The WD33C93A model covers both ways drivers run the bus, verified against the real 7.0 boot ROM booting a Workbench install end-to-end:

Data phases run through the DMAC handshake (a word per DMAC cycle into chip, slow, or Zorro RAM with the 24-bit ACR auto-incrementing) or through the PIO data register with DBR. Like the Gayle model, transfers complete within the access; completion interrupts are delivered after a short emulated delay, and INT2 is the level CNTR_INTEN && ISTR & (INTS|E_INT) fed to Paula’s PORTS latch each tick. DMAC bus-master cycles are not yet arbitrated against the CPU (TODO in a2091.rs).

A4091 (a4091.rs)

The A4091 is a Zorro III SCSI-2 controller carrying an NCR 53C710 and a nibble-wide autoboot ROM. Within its 16M window, $000000-$7FFFFF is the boot ROM presented nibble-wide (expansion.library reassembles the DiagArea with DAC_NIBBLEWIDE, and the ROM’s own relocator copies the driver the same way), $800000 is the 53C710 register file (only the low 6 address bits decode, so it mirrors across the window -- the driver relies on the +$40 shadow as a cache write-allocate workaround), and $8C0003 reads the DIP-switch byte (host ID, termination, negotiation enables). A DSP write starts the 53C710’s SCRIPTS processor, whose phase engine executes the driver’s SCRIPTS programs against the disk targets. The autoconfig identity is Commodore product 84 with er_InitDiagVec $0200.

A3000 Super DMAC (sdmac.rs)

The SDMAC is the SCSI DMA controller on the A3000 motherboard, not a Zorro board: a register file at $DD0000 (repeating at $DD0100 -- the “ALT” shadow that write-through tools use to defeat CPU write buffering) that owns the DMA FIFO and interrupt plumbing and maps a WD33C93’s register file into a select latch and data port. It is the same layering as the A2091 -- two front-ends onto the one Wd33c93 core -- differing in the register map, the ISTR bits, and a 32-bit DMA address counter (physically in Ramsey) instead of the Zorro II DMAC’s 24-bit one. Kickstart’s built-in scsi.device drives the pair directly, so there is no boot ROM to configure.

Shared drive backend

All IDE and SCSI drives share the harddrive.rs sector backend: raw HDF images, bare partition hardfiles wrapped in a synthesized RDB (bootable DHn named after the unit), gzip-compressed hardfiles (.hdz, sniffed by gzip magic and unpacked by gzip.rs into memory at open time because deflate has no random access, which is what makes their writes session-only), and host directories built into in-memory FFS or OFS volumes by dirfs.rs (FFS by default; filesystem = "ofs" on the drive picks OFS, the one every Kickstart from 1.2 onward can read with no guest-side setup -- FFS needs a handler loaded from disk or an RDB FileSystemHeader chain, neither of which Copperline bundles). The volume label defaults to the directory name, or a name override configured on the drive. The SCSI-2 target layer in scsi.rs answers INQUIRY, MODE SENSE pages 3/4, READ CAPACITY, READ/WRITE(6)/(10), REQUEST SENSE, and the no-op housekeeping commands, with sense state kept per target.

The drive controllers latch read/write activity, which the bus drains to light the status-bar HDD LED; the LED holds for a short minimum period so brief accesses stay visible. Gayle, the A4000 IDE, the A2091, the SDMAC, and the lide-compatible board (below) report activity today; the A4091 shows the LED but does not latch activity into it yet.

lide.device-compatible Zorro II IDE (ide_zorro.rs)

[lide] attaches a Zorro II IDE board compatible with LIV2’s actively-maintained open-source lide.device, in three AutoConfig personalities selected by board: RIPPLE (mfg 0x144A/product 7, two ATA channels), RIDE (mfg 0x144A/product 9, one channel, sharing RIPPLE’s ROM image and register layout), and AT-Bus 2008 (mfg 0x082C/product 6, one channel, the register model shared by that board’s whole clone family). All three reuse the front-end-agnostic ATA core in ata.rs (the same one Gayle and the A4000 IDE port use) and the shared drive backend above; the new work is entirely in the board’s own address decode, since none of the three personalities resemble Gayle’s 4-byte task file. Drive slots may be ATA hard disks or, since ata.rs gained ATAPI PACKET support, .cue/.iso/.chd CD-ROM images.

Register decode. Each ATA channel occupies a 4K block of the board window, with register index (offset >> 9) & 7 -- ATA A0-A2 are wired to CPU A9-A11, so a register answers throughout its 512-byte slot, which is what lets the driver bulk-transfer a sector with movem.l. Every register but the 16-bit data port sits on the upper byte lane (even addresses, D15-D8); the odd lane floats. RIPPLE’s two channels sit at window offset $1000/control $5000 (channel 0) and $2000/$6000 (channel 1) -- two chip selects per physical connector, task file and control block, per the RTL’s own decode; RIDE and AT-Bus 2008 have one channel at $1000, control block at $2000 (so $2C00 is the alternate-status register the driver’s channel-autodetect polls against $1E00). A channel with no drives attached at all floats every register, not only status: AtaBus::read_reg only special-cases status/alt-status for “no drive selected”, so the front-end checks AtaBus::any_drive_attached itself -- without it, an empty channel’s device/head register reads a hard zero, which real lide.device reads as “a device answered” and polls forever waiting for it to respond. (Found and fixed by booting a downloaded lide.rom under RIPPLE with only channel 0 populated -- see ide_zorro.rs’s tests and module docs.)

ROM window and banking. The flash is byte-wide, so a 32K bank fills 64K of window at even addresses (stride 2; the odd lane on AT-Bus 2008, whose er_InitDiagVec is 1 rather than 8 for exactly this reason). Before the first write anywhere in the window, ROM covers the whole window (bank selected by address bit 16 -- bank 1 being the optional CD filesystem); that first write latches ide_enabled, after which ROM remains only in the upper 64K (RIPPLE also keeps it in the low 64K wherever address bits 12 and 13 agree, which is exactly where the register blocks above are not). The bank register is written anywhere in $8000-$FFFF: RIPPLE has two banks and it is write-only; RIDE has four and reads back with otherram_en/maprom_en on the next nibble down. AT-Bus 2008 has no latch and no banking: its image sits on the odd lane across the whole window, always. None of the three boards wire an interrupt line -- lide.device is a purely polling driver.

ROM is always user-supplied (rom, optionally rom_bank2): LIV2’s GitHub releases ship lide.rom (RIPPLE/RIDE), lide-atbus.rom, and cdfs.rom, all 32768 bytes; Copperline never bundles or distributes them. Omitting rom is hardware-only mode: no DiagArea, no autoboot, diag_vec absent from the BoardSpec, but drives still answer once a disk-loaded driver finds them.

All three personalities have booted a real lide.rom/lide-atbus.rom release end-to-end to a real Workbench (Kickstart 1.3 and 3.1, --cpu 68020): AutoConfig, the DiagArea, lide.device loading as a resident module, finding an attached drive, and mounting a boot node from a real RDB image.

AT-Bus 2008’s ROM and register blocks share address space by byte lane (ROM odd, registers even, per above), including inside the control block at $2000: the board’s read dispatch used to match the control block first regardless of lane, so odd-lane reads there -- exactly where the boot ROM’s chainloader fetches its relocatable driver payload -- floated as an unpopulated register instead of reaching ROM. lide.device never loaded and the machine never got past the “insert disk” screen; RIPPLE and RIDE were unaffected, since their ROM sits on the even lane, clear of any register. Fixed by checking the ROM lane ahead of the register-block dispatch in IdeZorro::read() (see ide_zorro.rs’s tests).

Host filesystem service (filesys.rs)

[[filesys]] mounts export host directories as live AmigaDOS volumes (HOSTFS0: ... up to 8 mounts), with no disk image in between -- distinct from the dirfs.rs path above, which snapshots a directory into an in-memory FFS or OFS volume behind a virtual drive. The guest side is a tiny handler (see guest/services/) mapped into the Copperline services board with a mount table and a hand-built DiagArea. DiagPoint only patches a Romtag into the retained diag copy; Kickstart’s cold-start resident scan calls its rt_Init once DOS-list surgery is actually safe (doing it straight out of raw DiagPoint context corrupts Kickstart 1.3’s own boot), and rt_Init builds one DeviceNode per mount and AddBootNodes it (at the mount’s configured boot priority), so DOS mounts the devices at boot. The handler probes the library versions at runtime and falls back to the 1.3-era calls on Kickstart 1.3: AddDosNode for a non-boot mount, and a hand-built BootNode Enqueue()d on eb_MountList (mirroring the V34-era A590/A2091 boot ROM recipe) for a bootable one, so bootpri boots the machine from a hostfs volume on 1.3 exactly as it does on 2.0+. V34’s own boot-time handler startup carries BCPL process parameters rather than a V36 ACTION_STARTUP (dp_Arg3 is NULL; the handler locates its unit through dp_Arg2’s FileSysStartupMsg instead). The handler forwards every DosPacket to the host through a doorbell register in the board’s MMIO window: writing the packet APTR to REG_DOSPKT services the packet synchronously inside the register write, so dp_Res1/dp_Res2 and the result registers are filled before the next guest instruction runs. All ACTION_* semantics -- reads, writes, create/rename/delete, directory walks, protection, comments, datestamps -- are implemented host-side against the real filesystem, with results written straight into guest memory.

Each mount unit owns its own bank of longword registers in the window (layout shared with the guest via guest/services/copperline_board.h): REG_MSGPORT publishes the handler process’s MsgPort while the unit is live, and REG_RESULT/REG_ARG tell the handler what to do with the packet it just rang in (reply it, AddDosEntry a host-built volume DosList node, or exit on ACTION_DIE). One handler process runs per unit against its own bank, so mounts never synchronize with each other. A single global DIAG_DOORBELL strobe carries the expansion-init work, which runs before any handler process exists. That init strobe is also where [machine] rom_scsi_device_disable takes effect: the board’s DiagPoint culls the ROM’s scsi.device resident tag (romtags.rs), which is why setting the flag instantiates the services board even with no [[filesys]] mounts configured.

These longword registers are written with a single move.l in the guest ROM/handler, but on a 68000/68010 that compiles to two word-sized bus cycles (high word, then low word -- a real 16-bit-bus artifact the CPU core reproduces). The board fires each doorbell (DIAG_DOORBELL, REG_DOSPKT, REG_MSGPORT) on whichever write actually completes the value -- a single 4-byte access on a 32-bit bus, or the low word of a split pair on a 16-bit one -- reading the result back out of the already- latched window image rather than trusting the write that triggered it.

Amiga attributes a host filesystem cannot hold live in UAE-style .uaem sidecar files (read when present, written back on change, hidden from guest listings); the delete-protection bit is honoured on ACTION_DELETE_OBJECT. Filenames map between host UTF-8 and guest Latin-1, hiding names with no Latin-1 spelling; host symlinks are followed (the guest cannot create one, so a symlink is the host user deliberately grafting a tree into the mount), while path escapes that a guest could construct on its own (.., embedded separators) are blocked. A readonly mount refuses writes with the standard write-protection error.

A2065 Ethernet (a2065.rs, net/)

The [a2065] option fits a Commodore A2065: a Zorro II board carrying an Am7990 LANCE and 32 KiB of on-board RAM, driven by the AmigaOS SANA-II a2065.device. Unlike the DMAC boards the LANCE never masters the Amiga bus: its init block, descriptor rings, and packet buffers all live in the board’s own RAM, which the CPU reaches through the board window, so the board is self-contained and owns a host NetBackend (net/) for real frames. The LANCE engine models the Am7990 programming surface a real driver exercises: TX and RX buffer chaining (STP..ENP spans across descriptors), the stored FCS trailer (MCNT counts it; drivers read the payload as MCNT - 4), the init-block MODE gates (DTX/DRX and the LOOP internal-loopback self-test SANA-II drivers run at power-up), and MISS on an RX ring overrun.

The nat backend (net/nat/, net-nat build feature) is a slirp-style userspace NAT: a dedicated a2065-nat thread owns a smoltcp interface that terminates ARP and the guest’s TCP on the virtual gateway (10.0.2.2, DNS forwarder 10.0.2.3, guest 10.0.2.15/24), splices each TCP flow onto a non-blocking host socket, NATs UDP per flow, resolves DNS through the host’s own resolver, and answers BOOTP/DHCP and ICMP echo at frame level. Frames cross to the emulated NIC over bounded channels that drop on overflow, so the emulator thread never blocks on the host network. Networking is inherently non-deterministic, so a fitted NIC breaks byte-identical replay while traffic flows; save states record only the chosen backend and bring up a fresh one on load (flows die; the guest’s TCP retransmits). The board and backend story, including the WASM plugin net capability, is covered in Writing Zorro board plugins.

The bridge backend (net/bridge/, net-bridge build feature) uses the same bounded worker boundary but carries unmodified Ethernet frames to a selected physical adapter: AF_PACKET on Linux, system libpcap/BPF on macOS, and runtime-loaded Npcap on Windows. A platform filter and a second software guard admit only the guest station address and multicast/broadcast, while guest-source capture echo is discarded. The LANCE’s init-block PADR updates that filter. Linux’s companion process owns only CAP_NET_RAW, validates an interface request, and passes a bound descriptor with SCM_RIGHTS; it never handles a frame. Backend construction is fallible so bridge errors abort machine startup or state restoration rather than changing connectivity.

HostSocket (hostsocket.rs, crates/hostsocket-plugin/, guest/hostsocket/)

The [hostsocket] option fits the bundled HostSocket board: guest-facing bsdsocket.library backed by a smoltcp TCP/IP stack on the host, so socket applications run with no guest network stack at all. It is deliberately not a native device like the A2065 but a WASM plugin board hosted by wasmboard.rs, with its module and guest stub ROM embedded in the binary (hostsocket.rs holds the bytes and expands the config section into an ordinary plugin-board entry whose module path is a sentinel the plugin host and save-state restore resolve). The plugin boundary is what makes the board save-state-clean: the entire TCP/IP stack -- smoltcp interface, socket set, fd table, DNS state -- lives in the module’s linear memory, which snapshots and restores byte-for-byte like Amiga RAM; a native port would have to hand-serialize live smoltcp state, which smoltcp does not support. The guest side (guest/hostsocket/) installs the library via an rt_Init-deferred Romtag (safe on real Kickstart 1.3/3.1 and AROS) and stages each LVO through a Forbid-bracketed register-window RPC, with a wake-queue interrupt path for blocking calls -- the same host-does-the-work pattern as the services board’s hostfs handler. The board reuses the shared NetBackends above through the plugin net capability; loopback is deterministic, nat/bridge are not. gethostbyname() defaults to the plugin ABI’s resolve capability under net = "nat"/"bridge" (resolve_start/resolve_poll in wasmboard.rs, register_host_fns), resolving via the host’s own OS resolver on a short-lived background thread -- the same getaddrinfo-on-a-thread shape the NAT DNS forwarder above already uses, reused directly (net::nat::dns::resolve_a) rather than reimplemented -- so it works out of the box under net = "bridge" with no dns_server hand-configured to match the LAN. [hostsocket] resolver = "dns" opts back into the board speaking DNS itself over that same net traffic, to target a specific server instead of the host’s own resolver. The library’s own LVO table covers the real bsdsocket_lib.sfd order from socket() all the way to the table’s real end at LVO -858 (confirmed against Olaf Barthel’s own authoritative .sfd, not just the -30..-300 range Phase 4 originally shipped, and not just the AmiTCP-4.0-compatible subset through ObtainServerSocket at -696) -- inet_aton/inet_ntop/ inet_pton, In_LocalAddr/In_CanForward, the setservent/setprotoent/ setnetent iterator families, and Roadshow’s own resolver-family extension (getaddrinfo/getnameinfo/gai_strerror/freeaddrinfo, plus the reentrant gethostbyname_r/gethostbyaddr_r) all get real bodies too, while the LVOs with no equivalent in this project’s model (raw packet capture, host routing tables, live interface reconfiguration, direct BSD mbuf-chain manipulation, Roadshow’s own internal global-data-access functions) stay _hs_stub rather than jumping off the end of the table (see guest/hostsocket/entry.s’s own jump-table comment for the full accounting).

CDTV (cdtv.rs, cdrom.rs)

The CDTV model pairs the DMAC (which autoconfigs ahead of the Zorro chain, as on the real machine -- the CDTV firmware requires the DMAC to be the first configured board) with a Matshita drive speaking its fixed-length command/response protocol: seek, read, play (LSN/MSF/track), status, SubQ, and TOC queries, with responses delivered byte-by-byte with STEN pulses. Data sectors DMA onto the system bus at the 24-bit ACR address -- chip, slow, or Zorro board RAM, like the A2091’s DMAC; Kickstart allocates the CD buffers in fast RAM when a board is fitted -- paced at single speed and raising the DMAC interrupt on completion. The 256 KiB extended ROM sits at $F00000.

CD32 Akiko (akiko.rs)

Akiko sits at $B80000 with its $C0CACAFE ID: the chunky-to-planar converter, the I2C lines to the 24C08 NVRAM EEPROM (persisted to the [cd] nvram file), and the CD command/response rings talking to a Chinon drive model (stop, pause, seek/play/read, LED, SubQ, status). Data sectors stream as 2352-byte raw frames at 75 (or 150 at 2x) sectors/second; CD audio mixes into the host output, and both light the blue CD LED. The 512 KiB extended ROM sits at $E00000, and the CD32 pad protocol drives port 2.

cdrom.rs parses BIN/CUE cue sheets (single- or multi-file; MODE1/2048, MODE1/2352, and AUDIO tracks) for both machines.

RTC (rtc.rs)

An MSM6242-compatible register view at $DC0000, present on machines configured with rtc = true. Reads reflect host time; guest writes only affect the emulated latch/control state, never the host clock.

The part is four bits wide and wired to the low byte lane alone, so it answers on odd addresses while the even lane floats with the bus -- with or without a chip in the socket, since nothing else drives it either. The register select is A2-A5, so A1 does not reach the decode and each register answers at both of its odd bytes (register 0 at +1 and +3, register 1 at +5 and +7, ...); AmigaOS uses $DC0000 + N * 4 + 3 by convention, not because the part is deaf at +1. Writes take the same lanes as reads. With rtc = false the page still answers the cycle, and the odd lane reads back $40 (measured on real A500 hardware) rather than floating. That distinction matters: every OS clock probe -- AROS battclock.resource, 1.3’s SetClock, 2.0+'s battclock.resource -- decides a clock is present by writing a control nibble and reading it back, so a lane floating to the last value on the data bus eventually echoes the write and hands the guest an imaginary clock, and then an imaginary date.

Input (gamepad.rs, window input paths)

Host keyboard events translate to Amiga raw codes and feed a 6500/1 keyboard-MCU model (chipset/keyboard.rs) that clocks each event into CIA-A bit by bit over the emulated KCLK/KDAT lines: 60 us bit cells, the KDAT handshake after every byte (the MCU samples the line within microseconds and accepts any deliberate pulse, so software that reads the keyboard with a brief handshake -- e.g. Pinball Dreams at ~13.5 us -- works, not just the boot ROM’s longer pulse), lost-sync recovery (lone sync bits, F9,retransmission),theF9, retransmission), the FD/FEpower−upstream,theFE power-up stream, the 78/KCLK-low reset protocol behind Ctrl+Amiga+Amiga, Caps Lock’s keyboard-owned LED toggle, a 10-event type-ahead buffer with $FA overflow, and ghost suppression on the real A500 key matrix (the seven qualifiers are on dedicated lines and never ghost). The protocol was cross-checked against real-hardware-validated replacement keyboard firmware. Mouse deltas feed the JOY0DAT quadrature counters. Gamepads are read through raw gilrs events against the per-UUID calibration described in The window, status bar, and menus; on CD32 machines the pad output is serialized through the CD32 pad protocol instead of the plain digital joystick lines.

The window layer has one host-source policy for the emulated port-2 joystick/CD32 pad: gamepad (the default) or keyboard. Keyboard mode skips gamepad polling for port-2 input; gamepad mode disables keyboard joystick capture so the mapped keys take the normal Amiga keyboard path. (The old auto-detect mode has been removed; "auto" in a config parses as a backward-compatibility alias for gamepad.) Both sources ultimately call the same InputState::set_joystick_port2 and set_cd32_buttons_port2 helpers, so JOY1DAT, /FIR1, POT1Y/POTGOR, and the CD32 serial bits remain hardware-derived.

Keyboard joystick emulation is deliberately a host input source, not a guest-keyboard behaviour. When active, the winit key handler consumes the mapped host keys before rawkey translation: cursor keys drive directions, Right Ctrl/Right Alt drive fire, and the CD32 extras are C/X/D/S/Return/Z/A. Each alias is tracked independently before resolving to a single joystick state, so releasing one fire alias does not clear fire while another alias is still held. Releases for keys already captured as joystick controls are also swallowed if the source mode changes before key-up, preventing stray Amiga rawkey releases.

Audio output (audio.rs)

AudioSink abstracts the host boundary: a cpal live sink, a WAV-file sink (--audio-wav), and a null sink (--noaudio). Paula renders in emulated time; the live sink resamples and buffers against wall-clock. The CPAL_* lead/prebuffer/stale-drop targets in audio.rs are fixed rather than adaptive (currently a 131072-frame ring, a ~150 ms prebuffer equal to the ~150 ms steady lead, and a ~300 ms stale-drop threshold at 44.1 kHz). Playback starts only after the first audible frames have filled that prebuffer, so silent boot/load periods do not queue seconds of zeros. If the cpal callback later drains the queue completely, it stops playback, outputs silence, and waits for the same prebuffer depth before restarting. While an already-started queue is merely below target, the sink reports the missing buffer depth as extra live-audio lead so the real-time pacer runs ahead and restores the cushion without forcing a host-side silence gap first.

The live queue is host presentation state, not Paula state. A save-state or reverse-debug timeline jump keeps the restored Paula/CD/floppy mixer state but discards queued cpal frames from the abandoned timeline, then rebuilds the live prebuffer from the restored emulated audio stream. Offline WAV capture is not affected by any of this buffering policy.

Two profiling knobs cover the audio/pacing boundary, both emitting one info line per second:

Default live-audio warnings are emitted from the producer side at the same one-second cadence, and only when an underrun, overrun, or stale-frame counter is nonzero.

Serial (serial.rs)

Paula’s SERDAT transmit path lands on a SerialSink. The default StdoutSink prints to the host terminal -- this is how DiagROM’s diagnostic stream and the timing-test/ results are captured in terminals and CI logs. TcpSerialSink bridges the port to a listening TCP socket ([serial] mode = "tcp", one client at a time) or dials out to a remote endpoint (mode = "tcp-connect" with connect = "host:port" -- the BBS-client wiring), and PtySerialSink bridges to a host pseudo-terminal pair (mode = "pty", Unix only); all are bidirectional, so an AUX: shell on the Amiga side gives a remote AmigaDOS console. The browser build swaps in a channel-backed sink that the page bridges to a WebSocket.

A SerialSink that can produce input must override has_pending_input alongside read_byte/read_word: Paula’s per-tick UART step takes an idle fast path that skips the receiver entirely while it reports false -- the TCP and pty sinks poll a counter there, never a syscall.

CCP serial observability is a host-side tap beside SerialSink, not another serial device. When a control connection subscribes, each successfully completed transmit word is copied into a 4,096-entry VecDeque; the normal sink receives the same word immediately. Overflow evicts and counts the oldest observation, so a debugger cannot back-pressure Paula. The tap is skipped by serde and carried across state loads with the live serial/audio sinks; disconnecting or unsubscribing removes it.

MIDI serial bridge (midi/)

[serial] mode = "midi" (or --midi-out/--midi-in) bridges Paula’s serial port to host MIDI, behind the optional midi cargo feature -- a plain build compiles none of it and the mode falls back with a clear message. The whole thing hangs off one SerialSink, MidiSerialSink, so the emulator core is unchanged from any other serial target.

The load-bearing detail is that byte timing survives to the wire. Paula stamps each transmitted byte with the emulated colour clock it left on (SerialTimeAnchor); MidiSerialSink maps that to a host Instant and asks the backend to schedule the message for that instant rather than send it now, so a frame’s worth of bytes flushed together still leaves at the original spacing. Two host-agnostic pieces sit above the backend: a MidiFramer reassembles the single-byte serial stream into whole MIDI messages (a receiver rejects lone data bytes), tracking running status and SysEx and passing interleaved real-time bytes straight through; and Active Sensing (0xFE) is forwarded by default -- a real Amiga passes it down the wire -- and only dropped under COPPERLINE_MIDI_STRIP_ACTIVE_SENSE=1. Input arrives on a lock-free SPSC ring the receiver drains on its idle fast path, so the poll never locks.

The host connection lives behind the MidiBackend trait, chosen by cfg(target_os): macOS drives CoreMIDI (coremidi.rs), Linux the ALSA sequencer (alsa.rs), and Windows WinMM (winmm.rs); any other target gets stub.rs, which enumerates nothing and refuses to open. Each backend links its platform library directly with no wrapper crate, and each maps the scheduled send onto that platform’s timed-delivery primitive: a CoreMIDI packet timestamp, an ALSA real-time queue event, or -- since WinMM carries no timestamp -- a scheduler thread that fires each message when it comes due. A new backend implements send/set_output/set_input/current_output/current_input plus free enumerate/open; nothing else changes. The raw FFI is layout-sensitive -- CoreMIDI packs its packet list to 4 bytes, the ALSA snd_seq_event_t scheduling helpers are header-only inlines whose field writes are replicated by hand, and WinMM’s MIDIHDR is packed -- so the mirrors are pinned with compile-time layout assertions and want checking against live MIDI, not just review.

Two debug knobs help tell a dead path from a routing one: COPPERLINE_MIDI_DEBUG=1 reports per-second tx/rx byte counts and the first bytes sent (no tx while a song plays means the guest is not driving serial, i.e. the fault is upstream of the bridge); =2 decodes every message in each direction. COPPERLINE_MIDI_IMMEDIATE=1 bypasses scheduling and sends each message for immediate delivery, to separate a timing problem from a connection one.

Parallel port peripherals (parallel.rs, sampler.rs)

The Centronics port’s peripheral boundary is the ParallelPort trait. CIA-A port B ($BFE101) carries the eight data pins and CIA-A’s PC output is the active-low printer strobe: the bus forwards each strobe with the physical pin levels, and a peripheral that accepts the byte returns true, which the bus turns into the printer’s active-low /ACK edge on CIA-A FLAG. An input peripheral instead drives the data pins itself on every CIA-A port-B read. The status lines BUSY, POUT, and SEL are CIA-B port A pins 0-2, peripheral-driven inputs with motherboard pull-ups. The default null peripheral is an unplugged cable: it neither acknowledges nor drives any pin, and the pulled-up status lines read all high.

[parallel] device = "printer" captures strobed bytes to the configured output file (FileParallelPort), holding the status lines at ready-online levels (SEL high, BUSY and POUT low) -- without those, parallel.device polls BUSY forever and never sends a byte. device = "sampler" fits the classic mono 8-bit parallel-port digitizer (AMAS/DSS-class, modelled on the open-amiga-sampler schematics): a host capture stream fills a ring in real time and each port-B read returns the sample for the elapsed emulated time, so recordings line up however fast or slow the Amiga polls. Samples are 8-bit offset-binary (128 = silence), host left and right are summed to the mono input, and the preamp gain is clamped to +/-24 dB. COPPERLINE_SAMPLER_DEBUG=1 logs the captured input level about once a second -- a CLI VU meter for checking the host microphone is feeding the port.

Internals
CPU integration
Internals
Save states (savestate.rs)