Document RG35XX Plus boot chain, reorganize device docs

Move device-specific content (hardware, software, libraries) from
TOOLCHAIN.md into new docs/rg35xx-plus.md. Add partition layout,
full boot chain trace (systemd → launcher.sh → loadapp.sh → dmenu_ln),
and sdlamp2 deployment instructions via dmenu_ln config toggle.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
Michael Smith 2026-02-13 15:18:59 +01:00
parent 4f6d1de8e2
commit a5b04fcd08
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SDLamp2 is a simple SDL2-based audio player written in C, designed for a child to use. It plays long m4a/mp3 files (fairy tale cassette rips) with a cassette-player-like UI: rewind, stop, play, fast-forward, next tape. Inspired by Winamp.
See `docs/sdlamp2-fsd.md` for the full functional specification and changelog.
See `docs/TOOLCHAIN.md` for target device details and the arm64 Docker build container.
See `docs/TOOLCHAIN.md` for the arm64 Docker build container.
See `docs/rg35xx-plus.md` for target device details, boot chain, and deployment.
## Build and Run

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# Cross-Compilation Toolchain
# Build Container
This document describes the target device and the arm64 Docker build container used to produce binaries for it.
## Target Device
### Hardware
- **Device:** Anbernic RG35XX Plus
- **SoC:** Allwinner H700 — quad-core ARM Cortex-A53 @ 1.5 GHz (AArch64 / ARMv8-A)
- **GPU:** Mali G31 MP2
- **RAM:** 1 GB LPDDR4
- **Display:** 640×480 IPS
### Software
- **OS:** Ubuntu 22.04 LTS (Jammy Jellyfish) — [modified stock firmware](https://github.com/cbepx-me/Anbernic-H700-RG-xx-StockOS-Modification)
- **Kernel:** Linux 4.9.170 aarch64 (proprietary, no source released by Anbernic)
- **Architecture:** aarch64 / arm64 (confirmed via `dpkg --print-architecture`)
- **glibc:** 2.35
### Libraries on Device
All required shared libraries are pre-installed. Most are at `/usr/lib/`, some at `/usr/lib/aarch64-linux-gnu/` (Debian multiarch path):
| Library | Soname | Notes |
|---------|--------|-------|
| SDL2 | `libSDL2-2.0.so.0.12.0` | SDL 2.0.12 |
| SDL2_image | `libSDL2_image-2.0.so.0.900.0` | SDL2_image 2.0.9, at multiarch path |
| libavcodec | `libavcodec.so.58` | FFmpeg ~4.x |
| libavformat | `libavformat.so.58` | FFmpeg ~4.x |
| libavutil | `libavutil.so.56` | FFmpeg ~4.x |
| libswresample | `libswresample.so.3` | FFmpeg ~4.x |
### Implications for Cross-Compilation
- The device userland is Debian/Ubuntu-based (has `dpkg`, `apt-get`, `systemd`)
- Shared libraries are already present — no need to bundle or build them via Buildroot
- A native aarch64 compile (e.g. inside an arm64 Docker container) produces working binaries
- Must link against glibc ≤ 2.35 (use GCC ≤ 12 to avoid GLIBCXX version mismatches)
## Build Container
arm64 Docker build container for producing device binaries. For target device details see [`rg35xx-plus.md`](rg35xx-plus.md).
The `docker-arm64/` directory contains a Docker setup that runs an arm64 Ubuntu 22.04 container via QEMU user-mode emulation. This matches the target device exactly — same distro, same glibc 2.35, same library versions. The project's native `make` (using `pkg-config`) works as-is inside the container, no cross-compilation flags needed.

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# Anbernic RG35XX Plus
Device-specific reference for the target hardware. For build instructions see [`TOOLCHAIN.md`](TOOLCHAIN.md).
## Hardware
- **Device:** Anbernic RG35XX Plus
- **SoC:** Allwinner H700 — quad-core ARM Cortex-A53 @ 1.5 GHz (AArch64 / ARMv8-A)
- **GPU:** Mali G31 MP2
- **RAM:** 1 GB LPDDR4
- **Display:** 640×480 IPS
## Software
- **OS:** Ubuntu 22.04 LTS (Jammy Jellyfish) — [modified stock firmware](https://github.com/cbepx-me/Anbernic-H700-RG-xx-StockOS-Modification)
- **Kernel:** Linux 4.9.170 aarch64 (proprietary, no source released by Anbernic)
- **Architecture:** aarch64 / arm64 (confirmed via `dpkg --print-architecture`)
- **glibc:** 2.35
- **Userland:** Debian/Ubuntu-based (`dpkg`, `apt-get`, `systemd`)
## Libraries on Device
All required shared libraries are pre-installed. Most are at `/usr/lib/`, some at `/usr/lib/aarch64-linux-gnu/` (Debian multiarch path):
| Library | Soname | Notes |
|---------|--------|-------|
| SDL2 | `libSDL2-2.0.so.0.12.0` | SDL 2.0.12 |
| SDL2_image | `libSDL2_image-2.0.so.0.900.0` | SDL2_image 2.0.9, at multiarch path |
| libavcodec | `libavcodec.so.58` | FFmpeg ~4.x |
| libavformat | `libavformat.so.58` | FFmpeg ~4.x |
| libavutil | `libavutil.so.56` | FFmpeg ~4.x |
| libswresample | `libswresample.so.3` | FFmpeg ~4.x |
Shared libraries are already present — no need to bundle or build them. A native aarch64 compile (e.g. inside the arm64 Docker container) produces working binaries. Must link against glibc ≤ 2.35.
## Partition Layout
| Device | Mount point | Filesystem | Contents |
|--------|-------------|------------|----------|
| `/dev/mmcblk0p5` | `/` | ext4 | Root filesystem |
| `/dev/mmcblk0p6` | `/mnt/vendor` | ext4 | Firmware, apps, scripts |
| `/dev/mmcblk0p7` | `/mnt/data` | ext4 | User data |
| `/dev/mmcblk0p8` | `/mnt/mmc` | vfat | ROMs |
| SD card slot | `/mnt/sdcard` | (varies) | External storage |
## Boot Chain
The device uses systemd but boots its UI through a SysV init script that systemd auto-wraps via `systemd-sysv-generator`. The chain is intentionally layered: `launcher.sh` runs before partitions are mounted (hardware setup), `loadapp.sh` runs after mounts (filesystem/network setup + app restart loop), and `dmenu_ln` is the app dispatcher.
```
systemd (graphical.target)
└─ launcher.service (SysV → auto-generated by systemd-sysv-generator)
└─ /etc/init.d/launcher.sh start
├── mounts /mnt/vendor
├── starts brightCtrl.bin (backlight daemon) &
├── starts cexpert &
└── starts loadapp.sh &
├── resizes root partition (first boot only)
├── mounts /mnt/data, /mnt/mmc
├── charging mode: if boot_mode==1 → charger UI → poweroff
├── normal mode: starts NetworkManager, bluetooth, wifi
├── syncs RTC, loads kernel modules, mounts SD card
├── runs /mnt/mod/ctrl/autostart (if exists)
└── RESTART LOOP: runs /mnt/vendor/ctrl/dmenu_ln repeatedly
└─ /mnt/vendor/ctrl/dmenu_ln
├── selects binary (default: dmenu.bin)
├── config overrides: muos.ini → muos.bin, vpRun.ini → ...
├── runs binary via app_scheduling()
└── on exit: executes /tmp/.next (app dispatch for menu)
```
### Why the indirection?
- **`launcher.sh`** — Pre-mount hardware setup: mounts `/mnt/vendor`, starts backlight and system daemons. Runs as a SysV init script so it integrates with systemd's boot ordering.
- **`loadapp.sh`** — Post-mount filesystem/network setup: mounts data partitions, handles charging mode, starts networking, then enters the restart loop. Runs in the background (`&`) so `launcher.sh` can return.
- **`dmenu_ln`** — App dispatcher: selects which binary to run based on config files, wraps execution in `app_scheduling()` (which sleeps 30s on crash before retrying), and supports `/tmp/.next` for menu-driven app switching.
### `app_scheduling` behavior
The `app_scheduling` function in `dmenu_ln` runs the selected binary. If it exits with a non-zero status, it sleeps 30 seconds before returning, which prevents crash loops from consuming all CPU. The outer `while true` loop in `loadapp.sh` then re-invokes `dmenu_ln`, restarting the application.
## Deploying sdlamp2
### Overview
The `dmenu_ln` script already supports switching the startup binary via config files (e.g. `muos.ini``muos.bin`). We follow the same pattern to launch sdlamp2 instead of the default menu.
### Setup
1. **Copy the binary** to the device:
```sh
scp build/sdlamp2 root@<device>:/mnt/vendor/bin/sdlamp2
```
2. **Add the config check** to `/mnt/vendor/ctrl/dmenu_ln`. In the section where `CMD` overrides are checked (after the existing `muos.ini` / `vpRun.ini` checks, before the `app_scheduling` call), add:
```bash
if [ -f "/mnt/vendor/sdlamp2.ini" ];then
CMD="/mnt/vendor/bin/sdlamp2 /mnt/sdcard/Music"
fi
```
The unquoted `$CMD` in `app_scheduling` undergoes word splitting, so the path argument is passed correctly.
3. **Enable sdlamp2 on boot:**
```sh
touch /mnt/vendor/sdlamp2.ini
```
4. **Disable** (revert to normal menu):
```sh
rm /mnt/vendor/sdlamp2.ini
```
### What's preserved
Everything else in the boot chain continues to work:
- **Charging mode** — handled in `loadapp.sh` before the restart loop
- **LED/backlight control**`brightCtrl.bin` started by `launcher.sh`
- **Clean shutdown** — system shutdown scripts unaffected
- **Restart on exit** — if sdlamp2 exits cleanly (status 0), the restart loop in `loadapp.sh` re-launches it immediately
- **Crash recovery** — if sdlamp2 crashes (non-zero exit), `app_scheduling` sleeps 30s then the loop retries
- **Easy revert** — removing `sdlamp2.ini` restores the stock menu on next boot