Niimbot B1 — density → darkness firmware patch

⚠️ READ THIS FIRST

• This firmware is for the Niimbot B1 on firmware version 5.22 ONLY.
• Flashing across major versions (e.g. 5.x ↔ 6.x, or → 4.x) WILL BRICK your device. Do not flash these files to any other firmware version or model.
• This project is for experimentation and right-to-repair on hardware you own.
• No warranty. Provided as-is. The author takes no responsibility whatsoever if you brick your device or damage it in any way. You flash entirely at your own risk.

• Full print darkness on any label — including third-party / untagged / refill paper. Stock firmware throttles darkness on non-branded media; this removes that.
• The density setting actually controls darkness. Stock B1 firmware never wires the user's density value into the print head at all. This patch does:
  • D1 → coeff 270 … D5 → coeff 400 (linear: coeff = 270 + (d−1)·32.5).
  • D5 = solid black (identical energy to the proven full-quality build).
  • D3 is the practical minimum on typical paper; D1 suits high-sensitivity stock.
• Safe by design: density only ever reduces energy below the proven-solid D5, so there is no over-burn or print-line timing risk.

• Model: Niimbot B1 only.
• Firmware: 5.22 only. Check it in the Niimbot app or via src/niimbot_b1.py info.
• Expected md5: firmware/B1_5.22_density_coeff.bin → 023ff56326fe8c65f01b68f32ebdba99.

1. Connect the B1 by USB. On Linux it enumerates as a serial port, /dev/ttyACM0.

2. Flash with the niimblue-node CLI (needs Node.js; npx fetches it automatically):

   npx @mmote/niimblue-node flash -t serial -a /dev/ttyACM0 -n 5.22 \
     -f firmware/B1_5.22_density_coeff.bin

3. The printer powers itself off after flashing — press the power button to turn it back on. It re-enumerates as /dev/ttyACM0; this is normal, not a brick.

4. Set density in the Niimbot app (or your print tool) and print. You should see a clear D1→D5 darkness progression.

• firmware/B1_5.22_thirdparty_fullquality.bin — full darkness on any label, no density control (fixed solid). Same-major (5.x) safe.
• To go fully stock, reflash official 5.22 firmware from the Niimbot app / niimblue.

Do not flash the files here. Instead, hand the docs to a capable coding LLM and ask it to port the patch to your firmware dump:

• Feed it docs/B1_density_coefficient_checkpoint.md (the density work) and docs/B1_firmware_RE_checkpoint.md (the underlying darkness/coefficient model).
• Those document everything needed to redo it on another dump: the energy model (darkness = renderer_input × coefficient), how the real density byte was located, the renderer entry points to hook, the Cortex-M0 detour technique, the full cave assembly (src/B1_5.22_density_hooks.s + .ld), and the exact patch/byte map.
• Ask it to locate the equivalent renderer entries and density config byte in your dump and reproduce the input-scaling detours. Verify on paper before flashing.

src/niimbot_b1.py prints 384-px-wide images over USB. Print each test-labels/dtest_D*.png at its matching density to confirm the progression:

python3 src/niimbot_b1.py info                 # check firmware version first
python3 src/niimbot_b1.py image test-labels/dtest_D3.png --density 3