Connecting AMYboard to Tulip over grove (I2C host) can send Tulip into a power boot loop

## Summary Several users report that connecting an **AMYboard** to a **Tulip CC** using the Tulip's **grove / STEMMA I2C header** and the AMYboard's back **"tulip" I2C host port** sends the Tulip into a **power boot loop** (it resets repeatedly at/before the REPL). This is the documented, supported hookup — from [docs/amyboard/README.md](https://github.com/shorepine/tulipcc/blob/main/docs/amyboard/README.md#L114): *"you can directly connect your AMYboard to it via the GROVE port and the back I2C HOST connector. Tulip will power and communicate with the AMYboard!"* ## Leading hypothesis: the Tulip's power source can't feed both boards When the AMYboard is connected this way and isn't separately powered, it pulls its power from the 3.3 V on the Tulip grove port. Our own docs give the numbers: - **An AMYboard draws ~350 mA from the 3V3_IN line** over the I2C/grove connection ([faq.md, "How many can I power over the I2C chain?"](https://github.com/shorepine/tulipcc/blob/main/docs/amyboard/faq.md#L249)). The AMYboard *"uses the highest voltage present"*, and the I2C host / grove input is **3.3 V from the Tulip** ([faq.md, "How do I power it?"](https://github.com/shorepine/tulipcc/blob/main/docs/amyboard/faq.md#L38)). - **Tulip alone already draws ~575 mA @ 5 V** (display at medium brightness) ([README.md:60](https://github.com/shorepine/tulipcc/blob/main/README.md#L60)), and the docs already say the **USB adapter should support at least 1 A** ([troubleshooting.md](https://github.com/shorepine/tulipcc/blob/main/docs/troubleshooting.md#L28)). Adding ~350 mA @ 3.3 V (≈ **+230–350 mA @ 5 V** once you account for the regulator and losses) on top of Tulip's ~575 mA @ 5 V pushes the total toward — or past — what a marginal 5 V source can actually deliver. If the supply / cable / hub can't keep up, the 5 V rail sags, Tulip's 3.3 V regulator drops out, and the ESP32‑S3 brownout detector resets the chip. It then tries to boot, pulls the same current, browns out again → **boot loop**. Inrush is highest at boot, which fits a boot-loop symptom (rather than a mid-session crash). This lines up with the usual real-world culprits: - weak / old USB chargers (the ~0.5 A "computer USB port" class) - charge-only or thin high-resistance USB-C cables - powering Tulip from an unpowered hub - a low battery ## Light investigation — what I confirmed in the repo - The supported path is grove ↔ AMYboard back **"tulip" host port**; the AMYboard **front-panel** I2C is for accessories, the **back port is host / power-in** ([faq.md:110](https://github.com/shorepine/tulipcc/blob/main/docs/amyboard/faq.md#L110)). - AMYboard power inputs and the ~350 mA grove draw are as quoted above (measured ~2.94 V at the 4th board in a chain, per the same FAQ entry). - I found **no explicit ESP32 brownout-detector configuration** in the Tulip firmware (`tulip/esp32s3`), so it runs at the ESP-IDF default (brownout detector **enabled**) — consistent with a brownout-triggered reset loop. - I found **no current limiting / soft-start** on the grove 3.3 V rail, and **no power warning** in the quick-start docs about the extra draw when attaching an AMYboard. > Note: the +5 V-side current estimate and the regulator topology are *inferred*, not bench-measured — worth confirming on hardware. ## How an affected user can confirm it's power - Watch the Tulip serial/boot log for **`Brownout detector was triggered`** (or repeated resets). - **Power the AMYboard separately over its own USB-C** — it takes the highest voltage present, so 5 V USB-C will feed it instead of pulling 3.3 V from the Tulip. If the loop stops, it's power. - Try a **known-good ≥1–2 A 5 V supply and a quality data USB-C cable**, plugged straight in (no hub). ## Possible resolutions - **Docs:** add a power note to the AMYboard ↔ Tulip "Quick start - Tulip" section and Tulip troubleshooting — connecting an AMYboard adds ~350 mA, so use a ≥1–2 A supply or power the AMYboard on its own USB-C. - **Bench check:** measure the 5 V / 3.3 V rails at boot with an AMYboard attached on a 1 A vs 2 A supply; confirm brownout vs. regulator dropout vs. inrush. - If a firmware change can help (e.g. deferring high-current init, ramping display brightness at boot), treat as a firmware bug. ## Asks for reporters If you hit this, please share: Tulip hardware rev, what's powering it (charger/cable/hub/battery + rated amps), whether the AMYboard had its own power, and any boot-log output. --- *Filed from a maintainer investigation; numbers cited are from the repo docs unless marked inferred.*