# re-bba-rb — on-console test suite (GameCube) A `.dol` you run from Swiss that drives the adapter in Serial Port 1 and reports pass/fail per test on the TV. ## Build Needs devkitPro's `gamecube-dev` group (devkitPPC + libogc). The devcontainer installs it — if `DEVKITPPC` is unset, **rebuild the container**, since the toolchain is added in `.devcontainer/Dockerfile`. ```bash make # -> gc_bba_test.dol ``` Copy the `.dol` to your SD card (SD Gecko / SD2SP2) and launch it from Swiss. ## Controls | Button | | |---|---| | D-pad up/down | move | | A | open a suite / rerun the selected test | | X | run the selected suite | | START | run everything | | Y | clear all results | | B | back | ## What it tests | Suite | Proves | |---|---| | Identity | device enumerates: `04 02 02 00`, HIPR, NWAYS | | Registers | PAR0–5, IMR writable and read back; IR is write-1-clear | | Reset/control | NCRA RESET self-clears, SR holds | | EXI integrity | 200 reads with no bit errors; which EXI clock indices work | | Ethernet | MAC readback, 60-byte ARP transmit (TI), frame receive (RWP/RI) | | SPRAM/DMA | ring descriptor is well-formed; reads ≥ 0x100 stream until CS | ## Things that will bite you **The device ID is a ONE-SHOT.** Address 0 returns `04 02 02 00` only until the first NCRA reset clears `id_phase` in the gateware; after that it reads back NCRA. That is correct — it matches the GC's own init order — but it means the Identity test can only pass once per *console power cycle*. Run it before the Reset suite. On a re-run the app reports SKIP with an explanation rather than a misleading failure. **TI is not proof of transmission.** It only means `TXFrameDrain` handed the frame to the W5100. A frame can set TI and never reach the wire. The TX test says so; to confirm the wire, capture on a PC or watch the RX test pick up a reply. **The RX test needs traffic.** It waits ~2 s for any frame. On an isolated link with nothing talking it will fail legitimately — give the PC an address on the same subnet (the ARP the TX test sends is aimed at `10.0.0.50`, so `sudo ip addr add 10.0.0.50/24 dev ` makes the PC answer it and both tests pass together). **Never over-clock a register read.** Asking for N bytes and clocking more leaves stale prefetched bytes queued and desynchronises the *next* transaction — a deterministic every-Nth-read corruption that looks like a signal-integrity fault. `bba_read()` clocks exactly `len`; don't "round up" for convenience. **TXDATA takes one byte per transaction.** The register file's effective address auto-increments per data byte, so a 4-byte write to 0x48 would spill into 0x49–0x4B. `bba_tx_bytes()` does it correctly. ## Build status Builds clean (no warnings) with devkitPPC 16.1.0 / GCC 16 in the devcontainer: `gc_bba_test.dol`, ~172 KB, entry `0x80003100`. `.gitignore` excludes the build products — run `make` to produce the `.dol`. ## Self-update over the BBA (Z button) Press **Z**, then on the host: ```bash sudo ./scripts/send-dol.py gc_bba_test/gc_bba_test.dol ``` The flow is deliberately **receive → temp file → verify → rotate → boot Swiss**: 1. The new build arrives over the adapter into a staging buffer. 2. It is written to `.tmp` and **read back and compared**. 3. Only then is it rotated in: the existing build becomes **`.prev.dol`** and the temp file becomes `.dol` (default `/gc_bba_test.dol`, override with `--dest`). 4. The app then boots **`/boot.dol`** — your known-good Swiss. **Ordering is the point.** If the transfer, the write or the verify fails, the build you are currently running is still on the card untouched, so you can just try again. And once an update succeeds, the previous build is kept as `.prev.dol` — so if the *new* one turns out to be broken, boot the previous one from Swiss and transfer again from there. One generation back is enough to never get stranded needing an SD card reader. The temp file deliberately has **no `.dol` extension**: Swiss lists `.dol` files, and a half-written image Swiss offers to boot is exactly what this avoids. The backup keeps `.dol` precisely because booting it is the point. **The received image is never launched.** The only thing this ever jumps into is Swiss, which was already known good. So a broken test build costs nothing: Swiss comes up, and you load whatever you like from there, including the previous build. That is what makes the update recoverable without a power cycle or digging the SD card out. If the SD write or the verify fails, nothing is launched at all — you stay in the menu with a working app. `sudo` is needed for `CAP_NET_RAW`. The GC's MAC is discovered from its first ACK, so neither side needs an address configured. ### Why it is not IP Frames carry a private ethertype (`0x88B5`, IEEE 802 local experimental 1) and a 12-byte header: no ARP, no IP stack, no checksums, and no libogc network driver competing for the EXI channel. It reuses exactly the two paths the test suite already proves on hardware — `bba_tx_bytes()` for TX and the SPRAM ring at RRP for RX — so each update doubles as a few hundred round trips of soak testing through that path. ### ⚠️ Quiet the link first — the ring has no overflow protection ```bash sudo ./scripts/gc-testlink.sh up # static IP, no DHCP, NM off ``` Nothing in the gateware consumes RRP, so `RXFrameAssembler` keeps writing and **laps the reader** — the real BBA has RBFI for this and this design does not. The poll loop costs ~5 EXI transactions per frame (~200 µs) while a 100 Mbit link delivers a 342-byte frame every ~30 µs, and the ring is only 15 pages (~3–11 frames). Under continuous traffic pages are overwritten before they are read, and the "descriptor" you then parse is really frame data from the frame that replaced it. That is where a descriptor of `00 00 00 01` comes from. It is **not** a dropped write — it is someone else's bytes. The biggest offender is usually the host's own DHCP client broadcasting on that interface (a 342-byte broadcast). `gc-testlink.sh up` sets a static address and takes the device out of NetworkManager, which stops it. Disabling IPv6 and mDNS on that interface helps further. `netboot_receive()` detects being lapped (writer more than two thirds of the ring ahead), resyncs and continues rather than parsing untrustworthy bytes, and reports the count on timeout — but detection is not prevention. A busy link will still cost retransmissions. ### Stop-and-wait is load-bearing The gateware does not consume RRP, so `RXFrameAssembler` can overwrite ring pages the GC has not read yet — there is no overflow protection. One block in flight means the ring never holds more than one unread frame. Do **not** turn this into a sliding window without adding RBFI-style protection first. ### SD interfaces `netboot_sd_write()` auto-detects, trying SD2SP2, then SD Gecko slot B, then slot A. Note the SD Gecko in **slot A shares EXI channel 0 with the BBA** (channel 0, device 2); libogc arbitrates, but SD2SP2 sits on its own channel and avoids the question. ### Why the copier lives in assembly at the top of MEM1 A DOL's sections load from 0x80003100 upward — exactly where this program's own `.text` sits. A copier compiled as an ordinary C function would **overwrite its own instructions partway through the copy** and hang. So: - `netboot_reserve()` carves the top of MEM1 and hands it to `SYS_SetArena1Hi()`, so neither libogc nor `malloc` will touch it. - `netboot_stub.S` is copied into that region and executed *there*. It must stay strictly position independent: no globals, no literal pool, no TOC references, no calls — otherwise it reads from the address it was *linked* at instead of the one it is *running* at. - `netboot_launch()` checks every section (and BSS) against the reserved region and **refuses** if any would land on it. ### Failure behaviour - 30 s with no frames, or 5 s mid-transfer, aborts back to the menu. - A duplicate block is re-ACKed rather than ignored, so a lost ACK recovers. - `netboot_receive()` re-asserts the NCRA SR bit first: an earlier test may have left receive disabled, and it would otherwise wait forever for frames the gateware is not storing. - A failed SD write or verify launches nothing. - The residual risk is confined to booting `/boot.dol`. If that is a healthy Swiss, this is the safe part; if it is missing or corrupt, you get a message and stay in the menu — the new build is already on the card either way.