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DOOM on a 2007 Canon PowerShot SD1000 (IXUS 70) via CHDK. Loads from the SD card, no firmware flash.

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- AUDIO-WIP.md
- PORT-NOTES.md
- DOOM.BIN
- doom.flt
- chdk_syscalls.c
- doom_blob.ld
- doom_chdk_abi.h
- doom_printf.c
- doomgeneric_chdk.c
- gui_doom.c
.gitignore
build-blob.sh
LICENSE
README.md

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DOOM running on a 2007 Canon PowerShot SD1000 (IXUS 70 in Europe), a $300-at-the-time
point-and-shoot with a ~100MHz ARM and no FPU. It loads from the SD card via
[CHDK](https://chdk.fandom.com/wiki/CHDK). The Canon firmware is never modified and nothing
is soldered. Worst case at any point is pulling the battery.

Verified playable and snappy on camera, 2026-06-27. The prebuilt binaries in `prebuilt/`
are that exact build.

## How it works

CHDK's module system caps out around 100KB per module and its `elf2flt` chokes on newlib,
so DOOM doesn't run as a normal CHDK module. Instead:

- A tiny (~2KB) CHDK launcher module (`src/gui_doom.c` -> `doom.flt`) reads a standalone
  481KB flat DOOM binary (`DOOM.BIN`) from the card into the camera's 8MB RAW image buffer,
  which sits completely idle in playback mode. `hook_raw_image_addr()` hands you its address.
  I write-tested all 8MB before trusting it.
- The launcher fills a function-pointer callback table (ticks, sleep, key polling, screen
  blit, CHDK file IO, arena bounds), cleans the D-cache, invalidates the I-cache, and jumps
  to the blob's entry point.
- The blob is [doomgeneric](https://github.com/ozkl/doomgeneric) (GPL) compiled for ARMv5TE
  plus three small glue files: the six DG_* platform functions, a newlib syscall shim, and a
  hand-rolled printf (newlib's vfprintf hangs on this hardware with %d, plain strings were
  fine, that one took a while).
- DOOM is 16.16 fixed-point throughout, so no FPU needed. Canon's free heap is only ~670KB,
  but code, bss, and DOOM's zone heap all live in the raw buffer, so it doesn't matter.
- Display is DOOM's 320x200 8-bit frame blitted to CHDK's 8bpp palette overlay. The usable
  palette on this camera is only ~14 known-solid colors (the rest are semi-transparent
  dither), so colors are nearest-match. In-game looks fine, the title screen looks fried.
  Open item.
- No sound yet. The audio path (Wolfson WM1400 codec behind Canon's ASIF DMA engine) is
  reverse-engineered in `docs/AUDIO-WIP.md` but not wired up.

## Run it (prebuilt)

You need an SD1000/IXUS 70 on firmware 1.02a. Check yours with the
[ver.req method](https://chdk.fandom.com/wiki/FAQ#Which_firmware_version_do_I_have.3F).

1. Get CHDK 1.6 for `ixus70_sd1000` 1.02a from the [autobuild mirror](https://mighty-hoernsche.de/)
   and set up a bootable card per the [wiki guide](https://chdk.fandom.com/wiki/Prepare_your_SD_card).
   Use a 2GB or smaller card formatted IN CAMERA. Pre-2011 Canons only autoboot from true
   FAT16, and desktop formatters lie about that (macOS gave me FAT32 labeled FAT16 and the
   camera threw a memory card error).
2. Copy `prebuilt/DOOM.BIN` to the card root.
3. Copy `prebuilt/doom.flt` to `CHDK/MODULES/` on the card.
4. Put a standard shareware `DOOM1.WAD` at the card root
   ([where to get it](https://doomwiki.org/wiki/DOOM1.WAD)). It must be the standard
   shareware WAD. A repacked one I tried was missing the STBAR lump and crashed the status
   bar init.
5. Boot the camera in PLAYBACK mode (the raw buffer is only free when you're not shooting),
   press the shortcut/print button to enter ALT mode, then MENU > Games > DOOM.

### Controls

| Button | Action |
|---|---|
| d-pad | move / turn |
| SET | fire |
| shutter | use / open doors |
| shutter half-press | run |
| zoom lever | strafe |
| MENU | DOOM menu / esc |
| DISP | enter |
| PRINT | quit back to CHDK |

## Build it yourself

Toolchain is xPack arm-none-eabi-gcc 11.3.1 (CHDK's build system rejects newer GCC anyway):
[download](https://github.com/xpack-dev-tools/arm-none-eabi-gcc-xpack/releases/tag/v11.3.1-1.1),
extract, no install needed.

**The blob:** `./build-blob.sh` (set `XPACK=/path/to/toolchain/` if it's not on PATH).
It clones doomgeneric, drops in the glue from `src/`, compiles ~85 files with
`-march=armv5te -Os -DCMAP256`, and links a flat binary at `0x00E80000` with
`src/doom_blob.ld`, newlib nano and libgcc. The first two words of the blob are the entry
address and blob end, so the launcher never hardcodes them.

**The launcher:** built inside a CHDK source tree. Drop `src/gui_doom.c` and
`src/doom_chdk_abi.h` into `modules/games/`, register the module in `modules/Makefile` like
the existing games, and build for `PLATFORM=ixus70_sd1000 PLATFORMSUB=102a`. The `.flt` must
match the CHDK core revision on your card, so safest is building the whole core and
replacing it.

### The two traps that cost the most time

1. **Run cached.** The raw buffer address comes back as an uncached alias (0x10E80000).
   First boot ran there and was a slideshow. Strip the 0x10000000 bit, link and execute at
   the cached alias (0x00E80000), and it runs several times faster and fully playable.
2. **I-cache invalidation isn't exported to CHDK modules** (only `dcache_clean_all` is).
   Inline the ARMv5 CP15 op yourself: `mcr p15,0,r0,c7,c5,0`. Modules compile as Thumb and
   MCR is ARM-only, so the function must be `__attribute__((naked, target("arm")))` with its
   own `bx lr`. Skip this and you're executing stale cache lines after loading fresh code.

Full development log, including the dead ends, in `docs/PORT-NOTES.md`.

## Other cameras

Nothing here is SD1000-magic in principle: any CHDK-supported DIGIC III body has an idle
raw buffer and the same module APIs. But every address, the buffer size, the palette table,
and the key map are per-camera. Port at the level of the technique, not the binary.

## License

GPL-2.0, same as doomgeneric and the original DOOM source. The prebuilt `DOOM.BIN` contains
compiled doomgeneric; complete corresponding source is this repo plus
[ozkl/doomgeneric](https://github.com/ozkl/doomgeneric). DOOM1.WAD is not included; the
shareware episode is freely distributable but get it from an official mirror.

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