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• Bring-up Retrospective: 25 Days from PLAN.md to Seven Recipes

  roob123 • 15 hours ago • 0 comments

  Project log · Arduino UNO Q + GDEP073E01 7.3" colour e-paper · April–May 2026 Status: Beta 1 · 7 production recipes verified · 40+ memory documents on board

  Status flag for the community: This log contains corrections to several widely cited assumptions about GDEP073E01 — most importantly, the controller is SPD1657A, not SPD1656, and the seven-colour panel codebases that the community has been copying for the six-colour panel will silently fail in specific ways documented below. If you are working on Spectra 6, please read §VI–VIII before writing any custom-LUT code.

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  I. Project Summary

  The goal is to build a hardware-native carrier for AI coding workflows — a dedicated peripheral that displays the running state of Claude Code on a low-glare, reflective, always-on colour surface. The form factor we converged on:

  • Local agent host: Arduino UNO Q running Debian on its Qualcomm Dragonwing QRB2210 (4×A53 @ 2.0 GHz). Claude Code is installed on the board itself, not on a host PC. No network service is required between agent and display.
  • Real-time bridge: ST STM32U585 (Cortex-M33 @ 160 MHz, 786 KB SRAM) running Zephyr RTOS, driving the panel over 10 MHz SPI with strict timing.
  • Display: Good Display GDEP073E01 — 7.3", 800×480, 4 bpp, Spectra 6 colour, Solomon Systech SPD1657A controller.

  A 5-zone dashboard layout maps Claude Code's lifecycle events (UserPromptSubmit, PreToolUse, PostToolUse, Stop) to e-paper regions with throttling discipline (partial refresh ≥3 s, full refresh ≥60 s, force-scrub every 20 partials).

  This log covers the 25 days from drafting the design document to verifying seven reproducible production recipes for the 6→8-colour rendering pipeline. Most of those 25 days were not spent on waveform design — they were spent debugging the toolchain.

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  II. Bill of Materials

  Component	Specifics	Notes
  Arduino UNO Q	QRB2210 (Linux MPU) + STM32U585 (Zephyr MCU)	Dual-brain architecture; ~$70
  Good Display GDEP073E01	7.3" / 800×480 / Spectra 6 / 4 bpp	E Ink ACeP family, ~$45
  DESPI-C73	FPC-to-DIP adapter for GDEP073E01	Standard 8-pin breakout
  Wiring	7 × jumper wires, 3.3 V only	5 V kills SPD1657A; not warrantable
  USB-C cable	5 V / 3 A PD-capable	Direct drive — no external PSU needed (see §IV.3)

  Wiring map

  DESPI-C73 silkscreen	UNO Q pin	Notes
  3.3V	3V3	Not 5V
  GND	GND
  SDI	D11 (SPI2_MOSI)
  SCK	D13 (SPI2_SCK)
  CS	D10	See §III.3 — SPI2 NSS conflict
  D/C	D9
  RES	D8
  BUSY	D7

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  III. Phase 0: Three Bugs That Made "Upload Successful" Mean Nothing

  The first day on hardware (2026-04-20) produced no visible result on the panel despite three "successful" sketch uploads. Root cause analysis revealed three independent failure modes stacked on top of each other.

  III.1 The crab watcher service silently overwrites your sketch

  UNO Q ships with a Linux-side crab service that periodically rewrites the bound sketch back to a vendor default. Symptom: your code uploads, runs once, and then disappears.

  Fix:

  # Identify it
  adb shell ps -ef | grep crab
  
  # Stop and prevent restart
  adb shell sudo systemctl stop crab-watcher
  adb shell sudo systemctl disable crab-watcher
  

  III.2 arduino-flash writes to the bootanimation partition

  A more pernicious bug. The arduino-flash shell script hard-codes the target partition to bootanimation (presumably leftover boilerplate). Uploads report success — because the partition write did succeed — but the STM32 firmware never updates.

  The correct path is the arduino-app-cli flow:

  arduino-app-cli app create my-eink-app
  # (copy your sketch into the standard structure)
  arduino-app-cli app start my-eink-app
  

  Implication: every "successful upload" log line from arduino-flash should be cross-validated against actual MCU behaviour. We spent days debugging panel timing before discovering the firmware hadn't actually changed.

  III.3 SPI2 hardware NSS hijacks D10

  D10 on the UNO Q maps to STM32 pin PB9, which the Zephyr device tree pre-assigns...

  Read more »

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