LithosAnanake/FABRIC-3.md

# FABRIC-3.md — bare metal boot

**Status:** Living working document, opened 2026-09-04 as the successor to `FABRIC-2.md`
(now closed/archival — see its own header). Topic for this document, per direct instruction:
**bare metal boot** — getting LithosAnanke to actually boot on real hardware, not just QEMU.
`FABRIC-2.md` §I.6 (Milestone 8) already named this as the one item that pass couldn't close
from a coding session at all, for exactly this reason — it needs a real machine and a human
physically present. This document is where that work, and everything downstream of it, gets
tracked.

**How to use this document going forward.** New findings, new punch-list items, and new
decisions for bare-metal-boot work get added here, not to `FABRIC-2.md`. Same discipline every
prior document in this series used: write the decision and its reasoning down before building,
close items with a dated note citing real evidence, never silently drop a stale claim.

---

## I.1 — Task 1: merge `v2.0.1` into `master`, verify build/function equivalence

**Written up before executing**, per direct instruction and this series' own standing
discipline.

**Why this is task 1.** `FABRIC-2.md`'s entire 7-step closure pass (§I.1–§I.5, §I.7, plus
today's FABRIC-series rename) happened on the `v2.0.1` branch, not `master`. Before any real
bare-metal-boot work starts, that work needs to land where `.claude/CLAUDE.md` says the
project's sole production line actually lives: `master`. Doing this first, cleanly, before
starting new work avoids ever having two divergent lines to reconcile later.

**Investigated before writing this up, not assumed:**
- `git merge-base --is-ancestor master v2.0.1` — **true**. `master` (local HEAD `d2a0305`) is
  a strict ancestor of `v2.0.1` (HEAD `b031b80`) — `v2.0.1` is exactly `master` plus 47 commits
  forward, no divergent history on either side. This means the "merge" is a pure **fast-forward**,
  not a real three-way merge — nothing to resolve, no conflict possible.
- `origin/master` carries exactly one commit beyond local `master` (`58c59e8`, "Initial
  commit") that local `master` hadn't fetched yet — confirmed already contained in `v2.0.1`'s
  own history (`git merge-base --is-ancestor 58c59e8 v2.0.1` — true), so it introduces no
  discrepancy either.
- `master`'s own tree still has the *old* `FABRIC.md`/`FABRIC-2.md`/`FABRIC-3.md` naming
  (unrenamed) — expected, since today's rename commit (`b031b80`) only exists on `v2.0.1` so
  far. The fast-forward brings the rename to `master` along with everything else; nothing
  separate needs doing for it.

**Plan:**
1. Fast-forward `master` to `v2.0.1`'s tip (`git checkout master && git merge --ff-only v2.0.1`)
   — refuses loudly instead of silently doing a real merge if the ancestor relationship somehow
   isn't what the investigation above found, so this step re-verifies its own precondition.
2. Push `master` to `origin`.
3. **Verify build/function equivalence on a genuinely clean tree**, not by inference: `git clean`
   (after confirming nothing untracked-but-wanted is present), then the full acceptance sequence
   `.claude/CLAUDE.md` already mandates for any kernel change — `clean qemu` on all three
   architectures, in the foreground, one at a time, each reaching `ok>` and shutting down
   cleanly. Since the tree is byte-identical to `v2.0.1`'s post-fast-forward, this is expected
   to reproduce exactly what `v2.0.1`'s own last acceptance pass already showed — the point of
   re-running it here is to confirm that expectation holds on `master` itself, not to assume it
   from the fast-forward alone.
4. Return to `v2.0.1` as the working branch afterward (`.claude/CLAUDE.md`'s own rule: always
   return to the correct working branch after any out-of-branch work), unless told otherwise.

**DONE 2026-09-04, exactly as planned:**
1. Committed the write-up above on `v2.0.1` first (`72c14cb`), pushed. This became `v2.0.1`'s
   new tip.
2. `git checkout master && git merge --ff-only v2.0.1` — **Fast-forward**, `d2a0305..72c14cb`,
   confirming the investigated ancestor relationship held exactly as expected; no conflict, no
   merge commit.
3. `git push origin master` — `origin/master` moved `58c59e8..72c14cb`.
4. **Verified on a genuinely clean `master` tree**, not inferred from the fast-forward:
   - Hosted build (`make clean && make`): clean compile, zero warnings, same as `v2.0.1`.
   - Full 3-arch kernel acceptance (`clean qemu`, amd64/aarch64/riscv64, each in the foreground):
     all three reached `(zuse) ok>`/`ok>` and shut down cleanly, zero build errors, zero
     unexpected warnings — identical outcome to `v2.0.1`'s own last acceptance pass, confirmed
     directly rather than assumed. Logs: `logs/20260904-113208/amd64/`,
     `logs/20260904-113320/aarch64/`, `logs/20260904-113552/riscv64/`.
5. `master` and `v2.0.1` are now identical (`72c14cb` on both, `origin` and local). Returned to
   `v2.0.1` as the working branch per plan step 4.

**Task 1 closed.** `master` genuinely is the production line again, current through today's
FABRIC-series rename and the full `FABRIC-2.md` §I closure. Bare-metal-boot work (this
document's actual topic) starts from here.

## I.2 — Task 2: version correction — the `v2.0.1` bump and `v2.0.0` tag were premature

**Direct instruction, 2026-09-04**: the `LITHOS_VERSION` bump to `2.0.1` (and the branch name
that followed it) got ahead of the real state — per `Makefile.starkernel`'s own versioning
policy (`v2.0.0` = QEMU release, even major/LTS; `v2.0.1` = the SER5 hardware-track *line*,
RDRAND backend + thumbdrive image goal), claiming `2.0.1` implies hardware-track progress that
was never actually verified on real hardware — that verification is precisely `FABRIC-3.md`'s
whole open topic (§I.6 in the closed `FABRIC-2.md`). The current `master` HEAD is, correctly,
still a `v2.0.0`-class QEMU-only release. "Nothing harmful" — a version-label correction, not a
functional rollback.

**Found and fixed while correcting this, not left half-done:**
- A real gap in the FABRIC-series rename from earlier today: `Makefile.starkernel`,
  `Kconfig.kernel`, `scripts/bleach_zuse_img.sh`, four `proof/*.thy` files, and
  `src/starkernel/arch/amd64/isr.S` all still had stale `FABRIC.md`/`FABRIC-2.md`/`FABRIC-3.md`
  citations — the original sweep's file-list only matched `--include=*.md/*.c/*.h/*.4th`, which
  silently skipped every file without one of those four extensions. Found by re-grepping with
  the extensions excluded instead of included. Fixed with the same safe placeholder-substitution
  technique the original rename used (each file, one pass, ordered `FABRIC-3→2→1→0` placeholders
  then resolved) — verified no double-shifted or broken references remained afterward.
  `.claude/settings.local.json`'s own historical Bash-permission-grant log (literal past command
  strings naming the file as it was called *at the time*) was deliberately left alone — rewriting
  it would falsify an audit trail, not fix a stale citation.
- `ClaudeEXPORT/memories.json`/`conversations.json` also still reference the old names — left
  untouched on purpose, same reasoning as the memory note on that archive: it's a frozen export,
  mining material, not live documentation to keep in sync.

**Changes:**
1. `Makefile.starkernel`: `LITHOS_VERSION ?= 2.0.1` → `2.0.0`.
2. The rename-gap fix above (7 files).
3. Verified 3-arch boot (`clean qemu`, amd64/aarch64/riscv64, each in the foreground): all three
   show `LithosAnanke v2.0.0` in the boot banner (confirmed directly in each serial log, not
   assumed from the Makefile edit alone), zero build errors, zero unexpected warnings, clean
   shutdown.
4. Moved the existing `v2.0.0` git tag (previously at `2efd7fe`, the original QEMU-release
   milestone commit — that commit and its own message stay fully intact in history, only the
   tag pointer moves) to the current `master`/`v2.0.1`-branch HEAD, per explicit instruction —
   the prior tag placement was itself part of the same "got ahead of myself" correction, not a
   separate decision. No remote tag existed yet (`git ls-remote --tags origin` was empty for
   `v2.0.0`), so no destructive remote operation was needed, only a local move-and-push.
5. **Follow-up, same day**: `v2.0.1` (the working branch this and Task 1 happened on) deleted,
   local and `origin` — confirmed a strict ancestor of `master`'s new HEAD first, so nothing
   was lost. `master` is the repo's only branch from here on.

---

## II. Three architectures, three different hardware scopes

Per direct instruction, 2026-09-04. The real-hardware targets are **not** symmetric across
architectures — each gets its own section below because the actual scope of "done" is
different for each:

- **amd64 — genericity is the goal, not just the SER5.** The Beelink SER5 is the machine in
  hand and the development/reference target, but the real requirement is broader: this needs
  to boot on *any* x86_64 machine — laptop, desktop, tower, or mini PC — not just one vendor's
  quirks. SER5-only success is necessary but not sufficient; anything that works only because
  of an SER5-specific assumption (a particular ACPI table shape, a specific UEFI
  implementation's quirks) is a bug against this goal, not a deferred nice-to-have.
- **aarch64 — Raspberry Pi 5, and only the Raspberry Pi 5.** No genericity requirement across
  aarch64 boards — this is the one and only target for this architecture.
- **riscv64 — Milk-V Mars, and only the Milk-V Mars.** Same as aarch64: one specific board,
  not a generic riscv64-SBC goal.

**How to use sections III–V below.** Same discipline as everything else in this series: plan
before building, one section at a time, iterating — not all three architectures in parallel,
and not front-loading a complete plan before any real hardware is in front of us. Each section
starts with what's already true (existing repo infrastructure, already-decided policy) and
what's still genuinely unknown, not assumed.

## III. amd64 — generic x86_64 bare metal (reference hardware: Beelink SER5)

**Already true, not to be re-derived:**
- `ROADMAP.md`'s "Board-by-board hardware rollout" already names this `v2.2.0`'s gate: the
  generic GPT/FAT32 thumbdrive image (`make -f Makefile.starkernel ARCH=amd64 thumbdrive`,
  already built — `Makefile.starkernel:1018`) flashes to and boots on the real SER5 via its
  real UEFI, reaching POST + `ok>`, with the amd64 RDRAND entropy backend
  (`src/starkernel/rng/rng.c`, already built and part of `master`) serving live entropy.
- `iso-usb` (`Makefile.starkernel:1060`) is the alternate, novice-friendly path (UEFI
  isohybrid ISO for tools like GNOME Disks "Restore Disk Image...") — same underlying image,
  different flashing UX.
- `FABRIC-2.md` §I.6's own 8-step physical-boot sequence (build ISO, identify the target
  device, flash it, physically boot, decide an observation method, confirm POST, confirm
  `ok>`, document) is the closest thing to an existing plan — but it predates the genericity
  requirement and was written with no hardware in hand yet.

**Decided in conversation, 2026-09-04:**
- **Observation: HDMI (interactive) + serial (logged transcript), both.** The kernel's own
  VT100 framebuffer console (`console.c`/`vt100.c`/`framebuffer.c`) already gives a real
  interactive display over HDMI — no new code needed there. Serial capture, if the SER5
  exposes a UART header, uses the Raspberry Pi's own GPIO UART as the USB-serial bridge
  (already available hardware, not a purchase blocker) — this needs the SER5's own UART pins
  physically identified first (not yet confirmed it has an accessible header at all).
- **Genericity is verified by standards-compliance, not a second machine** — no second x86_64
  box is available right now. The bar is: nothing in the boot path may depend on an
  SER5-specific assumption (a particular ACPI table shape, a specific UEFI implementation's
  quirk) — argued by code audit against real UEFI/ACPI standards, not by testing on a second
  board, until one becomes available. This is a real constraint on the punch list below (item
  6), not a deferred nice-to-have.
- **Secure Boot: already disabled on this SER5.** No signed-loader work needed for this pass —
  "Secure Boot disabled in firmware setup" is the supported path, documented as such rather
  than built around.

**Punch list, this cadence's actual next steps:**
1. Build the generic thumbdrive image: `make -f Makefile.starkernel ARCH=amd64 thumbdrive`.
2. Flash it to a USB stick (`dd`, per the target's own existing usage message).
3. Physically inspect the SER5 for an exposed UART header/pins; if present, wire the
   Raspberry Pi's GPIO UART to it as the serial bridge. If absent, HDMI-only for this pass —
   not a blocker, just a scope note for step 7's log.
4. Connect HDMI + keyboard to the SER5.
5. Boot the SER5 from the flashed stick (firmware boot-order menu as needed — Secure Boot
   already disabled, confirmed above, so no signing prompt expected).
6. **Code audit pass** (can happen before or in parallel with 1–5, doesn't need the hardware
   in hand): review the amd64 boot path (`src/starkernel/boot/uefi_loader.c`,
   `arch/amd64/*.c`) for anything that assumes SER5-specific hardware rather than standard
   UEFI/ACPI — this is what "genericity" actually rests on per the decision above, not the
   SER5 boot succeeding alone.
7. Capture the boot: confirm POST reaches the same `1012/0/0` result QEMU shows, confirm
   `ok>`/`zuse)ok>`, confirm `rng: backend = rdrand` (live entropy, not the QEMU-only
   `virtio-rng` path), save the serial transcript (if wired) the same way `logs/` already
   keeps QEMU's.
8. Mint a Zuse identity on a second thumbdrive on the real SER5, confirm it re-attaches —
   the same real-hardware round-trip `ROADMAP.md`'s `v2.2.0` gate already names.
9. Update this section with results — pass/fail per step, any SER5-specific or genuinely
   generic-UEFI finding either way, before moving to aarch64.

## IV. aarch64 — Raspberry Pi 5

**Already true:** `ROADMAP.md` names this `v2.4.0`'s gate: boots on the real board, aarch64
peripheral-RNG backend live, Zuse mint/attach on real media. The peripheral-RNG backend itself
is **not yet built** — today's `rng_get_bytes()` (`src/starkernel/rng/rng.c`) only has a
`virtio-rng` path, real on QEMU, meaningless on real Pi 5 hardware (no virtio device there).

**Genuinely open, not yet decided:**
- Same observation-method question as amd64 (no QEMU serial socket on real hardware) —
  possibly shared tooling/approach across both boards once decided once.
- **A pinned GPIO VM, theory-stage** — see `FABRIC-4.md` §2. Raised in conversation, not yet
  scoped; downstream of §IV.1's own native-boot-flow work (a GPIO VM needs GPIO addresses
  from the DTB the same way the rest of this bring-up does).

### IV.1 — Boot-chain decision: UEFI vs. native, researched 2026-09-04

**Researched, not assumed** (web search, current as of this session):

**UEFI option investigated and found weak.** A real UEFI+ACPI firmware for Pi 5 exists —
[`rpi5-uefi`](https://github.com/worproject/rpi5-uefi) (TF-A + EDK2, SBBR-compliant). But:
it's **archived as of 2025-02-04**, support ended because newer Pi EEPROM firmware broke
compatibility with it; its own README says ACPI support is "under development and limited to
a few devices"; RP1 Ethernet/GPIO/PWM/EEPROM don't work under it. This kernel's whole
aarch64 boot path (`boot/uefi_loader.c`, `BootInfo->acpi_table`) assumes UEFI+ACPI the same
way amd64 and the QEMU aarch64 target do — but that assumption may not hold on a real,
current-firmware Pi 5 at all.

**Native boot flow — the real alternative, researched concretely:**
- Boot partition needs `bcm2712-rpi-5-b.dtb`, `config.txt`, and the kernel image itself —
  Pi 5 firmware defaults to loading `kernel_2712.img`, falling back to `kernel8.img` if that's
  absent.
- `config.txt` needs `os_check=0` for a non-Linux image, or the firmware assumes Linux and
  loads from `0x200000` instead of the classic Pi bare-metal load address `0x80000`.
- Entry protocol: `x0` = 32-bit DTB pointer (upper 32 bits of the 64-bit register
  unspecified — must mask before use), `x1`–`x3` reserved/zero. **No UEFI PE loader, no ACPI
  at all** — a completely different entry shape from `boot/uefi_loader.c`.
- Framebuffer: the VideoCore **mailbox property interface** (channel 8) — a real, different
  mechanism from UEFI GOP, no precedent anywhere in this codebase today.

**Decision, per direct instruction 2026-09-04: native boot flow.** Not UEFI. The archived,
partially-working UEFI project is too fragile a foundation to build a real-hardware release
on top of.

**What this actually means for the codebase, named honestly rather than estimated small:**
- A **new, non-UEFI entry path** for aarch64 real hardware — this kernel's boot sequence
  currently assumes `uefi_loader.c`'s PE-loader shape unconditionally on aarch64; a Pi 5
  native boot needs its own entry point (linked at `0x80000`, receiving `x0` = DTB pointer
  directly, no `BootInfo` from UEFI at all).
- A **DTB-driven `BootInfo` equivalent** replacing ACPI-sourced data for this path — memory
  map, peripheral addresses (UART, etc.) all come from the devicetree instead.
- **One real, genuine piece of reusable groundwork**: `starkernel/hal/fdt.c`/`fdt.h`, the
  minimal FDT reader already built for riscv64's `timebase-frequency` lookup
  (`arch/riscv64/timer.c`), is directly extensible for this — parsing `bcm2712-rpi-5-b.dtb`
  for peripheral addresses is the same kind of lookup, not a new mechanism.
- A **new mailbox-property-interface framebuffer driver** — genuinely new code, no existing
  precedent in this codebase, needed before the VT100 console framework
  (`console.c`/`vt100.c`/`framebuffer.c`) has anything to draw onto for this board.
- This is a real architectural fork for aarch64, not a small per-board addition — QEMU
  aarch64 keeps its existing UEFI+ACPI path unchanged; Pi 5 real hardware gets a second,
  parallel entry path. **Not yet scoped into a punch list** — that's the next step, once this
  fork's own shape (how much of `kernel_main.c`'s post-entry sequence can stay shared between
  the two paths vs. needs its own branch) is thought through.

### IV.2 — Peripheral RNG: unresolved, not just under-researched

`ROADMAP.md` names an "aarch64 peripheral-RNG backend" as part of `v2.4.0`'s gate. Researched
directly rather than assumed still-TODO: Broadcom's `iproc-rng200` block (real, on Pi 4/BCM2711
as `brcm,bcm2711-rng200`) has **no `bcm2712` compatible-string entry anywhere in current
mainline Linux** (checked the actual driver's `of_device_id` table directly). The RP1
companion chip's own published peripheral list (GPIO/USB/Ethernet/DMA/ADC/PLLs/SRAM/
UARTs/SPIs) doesn't mention an RNG either. Two real possibilities, not yet distinguished:
BCM2712 still has the RNG200 block but Linux hasn't wired it into a devicetree binding yet, or
it genuinely isn't exposed to the ARM cores this generation. No public register address exists
to target right now — this needs either a Broadcom datasheet (if one becomes available) or
direct hardware probing once the board is in hand (scan the known BCM2711 RNG200 offset region
on the BCM2712 memory map and see if anything responds — risky without a datasheet confirming
it's safe to touch, so likely a "board in hand, careful probe" task, not a today task).

## V. riscv64 — Milk-V Mars

**Already true:** `ROADMAP.md` names this (generically, "Milk-V") as part of `v2.5.0`'s gate:
boots on the real board, the Zkr (RNDR) entropy backend live. Same gap as aarch64:
`rng_get_bytes()` has no riscv64 hardware-RNG path today, only `virtio-rng`.

### V.1 — Boot chain: resolved, researched 2026-09-04

**Resolved, not left open.** The Mars is a documented mainline U-Boot board target in its own
right ([U-Boot docs — Milk-V Mars](https://docs.u-boot.org/en/latest/board/starfive/milk-v_mars.html)),
and it uses **the exact same U-Boot binaries as the StarFive VisionFive 2** — same SoC
(StarFive JH7110), board identity detected at SPL time, devicetree patched accordingly, no
separate Mars-specific firmware. This directly answers §V's own previously-open question:
**U-Boot + OpenSBI + devicetree, not UEFI** — same fork this kernel already decided for
aarch64 (§IV.1), now confirmed for riscv64 too.

**Boot chain, concretely:**
1. BootROM (ZSBL), StarFive's on-chip loader at `0x2A000000`, selects boot media by GPIO pins.
2. U-Boot SPL (FSBL) — initializes DRAM, configures PLLs.
3. OpenSBI (`fw_dynamic.bin`) — M-mode runtime services.
4. U-Boot main, S-mode, depends on OpenSBI.
5. Boot media: QSPI flash (recommended) or UART XMODEM (recovery). SD/eMMC boot modes are
   deprecated in current U-Boot.

**Entry protocol, from real VisionFive 2 bare-metal work (same SoC, directly applicable per
§VI's own cross-reference):**
- Entry point `0x40000000`.
- Core identification via the `mhartid` CSR — the SiFive S7 monitor core is hart 0, the four
  U74 application cores are harts 1–4 (matches the QEMU riscv64 target's own hart numbering
  convention already assumed elsewhere in this codebase — worth double-checking, not
  assuming, once real hardware is in hand).
- UART at `0x10000000`, 115200 baud, already initialized by firmware before handoff.
- Custom bare-metal images package via `vf2-imager` (invokes U-Boot's `mkimage`) into a FIT
  image — same tooling should apply to the Mars, unconfirmed until tried.
- **Not yet found**: what registers carry the DTB pointer/hart ID at the actual kernel entry
  point under this specific chain (the source consulted covered the image-packaging tooling,
  not the OpenSBI→kernel handoff register convention) — riscv64's standard Linux boot
  convention (`a0`=hart ID, `a1`=DTB pointer, S-mode entry) is the reasonable default
  assumption, matching what U-Boot/OpenSBI conventionally hand off, but not yet confirmed
  against this chain specifically.

**What this means for the codebase** — same shape of fork as aarch64 (§IV.1): a non-UEFI
entry path, a DTB-driven `BootInfo` equivalent (the existing `starkernel/hal/fdt.c` reader
extends here too, same as for the Pi 5), no ACPI. **Not yet scoped into a punch list.**

### V.2 — Peripheral RNG and Zkr: still genuinely open

- Zkr/RNDR instruction availability on the Mars's actual CPU (riscv64 Scalar Crypto extension
  support varies by implementation) — not yet confirmed; the VisionFive 2 bare-metal research
  above didn't surface this either, would need its own targeted look (or a real-hardware
  probe of `misa`/the Zkr extension discovery mechanism).
- Same observation-method question as the other two boards.
- **Whether the Mars needs the same pinned-GPIO-VM treatment as the Pi 5** — explicitly
  **not decided either way**, per direct instruction ("same for Milk-V (? not sure here)").
  See `FABRIC-4.md` §2. The Mars does have its own 40-pin GPIO header (§VI), so the open
  question is the VM architecture around it, not whether the hardware exists.

---

## VI. Hardware identification reference

Per-board SoC/CPU facts, consolidated here so later sections don't have to re-derive them.
Researched 2026-09-04 (web search, sources cited); anything not directly confirmed against
the actual unit in hand is flagged as such rather than assumed.

### amd64 — Beelink SER5 (reference/development machine)

- **CPU: AMD Ryzen 7 family.** Beelink has shipped the "SER5" name with several different
  Ryzen 7 SKUs over its product life (5700U, 5800H, 7735HS all confirmed to exist under this
  branding) — **exact SKU on this unit not yet confirmed**; check `dmesg`/BIOS/the physical
  unit when convenient (`cat /proc/cpuinfo` or the BIOS splash screen under Linux/before
  LithosAnanke boots, since LithosAnanke itself has no CPU-identification word yet). Not
  load-bearing for this document's own genericity requirement (§III) — the boot path must not
  depend on which SKU this is, by design — but worth pinning down for this reference's own
  accuracy.
- **Architecture generation**: Zen2 (5700U/5800H) or Zen3 (7735HS) depending on the SKU above
  — matters for any future CPU-feature-detection work (e.g. RDRAND is present on all of
  these; that part's already confirmed live via `rng: backend = rdrand`, §III).
- Sources: [Gentoo wiki — SER5 5560U](https://wiki.gentoo.org/wiki/Beelink_SER5_AMD_Ryzen_5_5560U_Mini_PC),
  [Starry Hope — SER5](https://www.starryhope.com/minipcs/models/beelink-ser5-mini-pc/),
  [Starry Hope — SER5 Pro](https://www.starryhope.com/minipcs/models/beelink-ser5-pro-mini-pc/),
  [Minixpc — SER5 Max](https://minixpc.com/blogs/news/beelink-ser5-max-review-powered-by-amd-ryzen7-5800h-processor).

### aarch64 — Raspberry Pi 5 (sole target)

- **SoC: Broadcom BCM2712.**
- **CPU**: quad-core 64-bit Arm Cortex-A76, 2.4 GHz, 512 KB per-core L2 cache, 2 MB shared L3.
- **GPU**: VideoCore VII, 12-core, 800 MHz, OpenGL ES 3.1 + Vulkan 1.2 (not relevant to
  LithosAnanke's own framebuffer work — that goes through the mailbox property interface,
  §IV.1 — but recorded here for completeness).
- **RAM**: LPDDR4X-4267, board variants at 1/2/4/8/16 GB, 32-bit memory interface, ~17 GB/s
  bandwidth.
- **I/O**: RP1 companion chip (PCIe 2.0 x4-attached) handles GPIO, USB 2.0/3.0, Gigabit
  Ethernet, CSI/DSI, analog video — confirmed separately (§IV.2) to have no RNG peripheral in
  its own published peripheral list.
- **Cortex-A76 and `FEAT_RNG` (ARMv8.5 `RNDR`/`RNDRRS`)**: not confirmed present — A76 is not
  among the cores that typically implement this feature (more common on newer cores like
  Cortex-X2/A710); if this matters for any future entropy-source decision, verify via `ID_AA64ISAR0_EL1`
  directly on the real board rather than assuming either way.
- Sources: [CNX Software — Pi 5 launch](https://www.cnx-software.com/2023/09/28/raspberry-pi-5-sbc-broadcom-bcm2712-quad-core-cortex-a76-soc/),
  [Raspberry Pi — Processors doc](https://www.raspberrypi.com/documentation/computers/processors.html),
  [sbcwiki — BCM2712](https://sbcwiki.com/docs/soc-manufacturers/broadcom/bcm2712/boards/rasperrypi-5/).

### riscv64 — Milk-V Mars (sole target)

- **SoC: StarFive JH7110**, 28 nm.
- **CPU**: 4× SiFive U74-MC application cores (RV64GC) + 1× SiFive S7 monitor core, up to
  1.5 GHz.
- **RAM**: up to 8 GB LPDDR4; storage via eMMC slot + microSD slot.
- **I/O**: 3× USB 3.0, 1× USB 2.0, HDMI 2.0 (4K), Gigabit Ethernet with PoE support, M.2 E-Key
  (WiFi/BT), 4-lane + 2-lane MIPI CSI, 40-pin GPIO header.
- **Physical**: designed to Raspberry Pi 3B dimensions — cases/heatsinks/fans for that form
  factor are compatible.
- **Multimedia**: H.264/H.265 4K@60fps decode, H.265 1080p@30fps encode (not relevant to
  LithosAnanke's own bring-up, recorded for completeness).
- Same JH7110 SoC as the StarFive VisionFive 2 — any VisionFive 2 bring-up material found
  while researching §V's own boot-chain question is likely directly applicable here too, worth
  checking first before assuming Mars-specific research is needed from scratch.
- Sources: [milkv.io — Mars overview](https://milkv.io/docs/mars/overview),
  [milkv.io — Mars product page](https://milkv.io/mars),
  [TinyComputers.io — Mars review](https://tinycomputers.io/posts/milk-v-mars-review.html).

### Noted for later, not yet in scope — BeagleBone Black

Added to this reference per direct instruction 2026-09-04, **recorded only — no work scoped
around it yet.** Genuinely different from the three targets above: the BeagleBone Black's
SoC is a **32-bit ARM** part, not aarch64 — a fourth architecture this kernel has no support
for at all today (amd64/aarch64/riscv64 only), not another board under an existing one.

- **SoC: TI Sitara AM335x.**
- **CPU**: single-core ARM Cortex-A8, 1 GHz, armv7-a (32-bit) — up to ~2000 MIPS.
- **RAM**: 512 MB DDR3L. Storage: 4 GB eMMC (default boot source) + microSD (secondary/
  overridable to primary).
- **Other on-die units**: PowerVR SGX530 3D GPU; 2× PRU (Programmable Realtime Unit) 32-bit
  200 MHz microcontrollers — real-time I/O coprocessors, no equivalent on any of the three
  boards above; crypto accelerators.
- **Boot modes**: eMMC, microSD, serial, USB.
- Sources: [element14 — BBB product page](https://www.element14.com/community/docs/DOC-84108/l/beaglebone-black-development-board-with-1ghz-am335x-arm%C3%A3%C3%A2-cortex-a8-processor),
  [TI.com — BEAGL-BONE-BLACK](https://www.ti.com/tool/BEAGL-BONE-BLACK).