Bitaxe – ESP32 Guru Meditation Error / Kernel Panic Backtrace

Open a serial monitor at 115200 8N1 (`idf.py monitor`, `screen /dev/ttyUSB0 115200`, `pio device monitor`, PuTTY on Windows, or Arduino Serial Monitor) and capture the next panic. Copy from the line containing `Guru Meditation Error` down through the `Rebooting...` line. Save it as a text file. Note the AxeOS version from the next boot's banner line `I (xxx) cpu_start: App version v2.x.y` — you need that exact version for backtrace decoding. Without the captured block you have nothing to decode and every subsequent step is a guess.

Read the exception class on the second header line. `(LoadProhibited)` / `(StoreProhibited)` is null pointer or freed pointer — usually a stratum or HTTP path bug. `(IllegalInstruction)` / `(InstrFetchProhibited)` is stack overflow or executing data as code. `(LoadStoreError)` / `(LoadStoreAlignment)` is unaligned memory access — struct-packing bug or hardware ESD. `(Cache disabled but cached memory region accessed)` is OTA / flash-during-ISR. Preceded by `Task watchdog got triggered.` is a blocked task — read the task name on that line first.

Cross-check the `EXCVADDR` register. `EXCVADDR: 0x00000000` is null pointer dereference — highest-confidence AxeOS NULL-check bug signal. `EXCVADDR: 0xffffffff` is uninitialized pointer (memory allocated but never assigned). `EXCVADDR: 0xa5a5a5a5` is stack canary violation, confirming stack overflow. `EXCVADDR` in the `0x3FCxxxxx` / `0x3FFxxxxx` DRAM range with valid memory means use-after-free. The `EXCVADDR` value plus the exception class narrows the diagnosis to one of six root causes before you decode anything.

Hard power-cycle (cold-unplug for 10 seconds), reflash the latest stable AxeOS factory image via the Bitaxe Web Flasher (https://bitaxe.org/flasher) in Chrome or Edge, and confirm whether the panic was a one-off or recurring. Reflashing alone clears half the panic causes — corrupt NVS partition with malformed pool config, mid-OTA half-write, image-vs-board mismatch. If the panic doesn't return within 24 hours it was transient; if it returns, you have a real reproducible bug worth decoding.

Install the ESP-IDF toolchain from https://docs.espressif.com/projects/esp-idf/en/latest/esp32s3/get-started/ — this gives you `xtensa-esp32s3-elf-addr2line` and `idf.py monitor`. The toolchain is open-source and runs on Windows / macOS / Linux. The install is the single biggest tool investment for serious Bitaxe debugging. Once installed, every backtrace from this Bitaxe (and the next one, and the next) is decodable in under 2 minutes.

Download the matching `esp-miner.elf` debug artifact for your exact AxeOS version from https://github.com/bitaxeorg/ESP-Miner/releases — releases ship the `.elf` alongside the `.bin`. Match the version exactly to the boot-banner line. A mismatched `.elf` produces wrong-but-plausible decoded function names — the hardest kind of bug to debug. Mirror every release `.elf` you flash to your local drive; releases occasionally get retagged or rebuilt.

Decode the backtrace addresses. From a terminal: `xtensa-esp32s3-elf-addr2line -pfiaC -e esp-miner.elf 0x42010234 0x420112ab 0x42011fff` (replace addresses with your actual backtrace, in order). The flags: `-p` pretty-print, `-f` show function name, `-i` show inlined frames, `-a` show addresses, `-C` demangle C++ names, `-e` specifies the ELF file. Output is one line per address: `0x42010234: stratum_thread at /path/to/esp-miner/main/tasks/stratum_task.c:182`. The first 2-3 frames are usually where the panic actually happened.

If you don't want to install the toolchain, use the browser-based decoder at https://maxgerhardt.github.io/esp32-exception-decoder/. Paste the entire panic block (header + register dump + backtrace) into the text area, upload your matching `esp-miner.elf` via the file picker, click Decode. Output is the same as `addr2line` but rendered in HTML. Slower than the local toolchain but zero install. Acceptable for one-off decodes; install the toolchain if you'll do this more than twice a month.

If the panic was preceded by `Task watchdog got triggered.`, read the task name on that line before any backtrace decode. Common Bitaxe culprits: `i2c_master_*` or `EMC2101` means the I2C bus is stuck (see bitaxe-i2c-handle-not-initialized for the deep dive); `stratum_task` means the pool socket hung past the watchdog window (try a different pool, or downgrade firmware); `wifi_task` means the WiFi driver wedged (hard reboot at the wall, then verify SSID / password); `IDLE0` / `IDLE1` means some other task is monopolizing the core (decode the backtrace per Step 7 — this is a serious firmware bug).

Search GitHub issues for your decoded function name plus the AxeOS version. URL: https://github.com/bitaxeorg/ESP-Miner/issues?q=is%3Aissue+stratum_thread (replace `stratum_thread` with your function). If a matching issue is open, comment with your panic block, decoded backtrace, firmware version, board revision, and any reproduction steps. Subscribe to the issue. If no matching issue exists, file a new one with the same artifacts. Open-source firmware moves at the speed of useful bug reports.

Downgrade to the last-known-good firmware as a workaround while waiting for an upstream fix. Reliable shelf-anchors: AxeOS `v2.7.1` for Gamma 601/602 (pre-`i2c_master.h` migration), the latest non-`b` (non-beta) tag for everything else. The Bitaxe Web Flasher exposes a `Choose firmware` dropdown that lets you flash any tagged release, not just the newest. Run the older build for 24 hours; if it's stable, stay on it until the upstream fix lands. Document the version pinning in your operations notes — future-you will need the reminder.

If the panic flavor is `(Cache disabled but cached memory region accessed)`, do NOT keep retrying OTA — you'll burn the second app partition into the same broken state. Force USB-C download mode (hold BOOT while plugging USB-C), then flash via the Bitaxe Web Flasher or `esptool.py write_flash`. The Web Flasher writes from outside the running firmware so the cache-during-ISR race never happens. Once you're on a build that doesn't ship the OTA bug, OTA is safe again.

If the panic header is `(IllegalInstruction)` with weird `PC` values (`0xa5a5a5a5`, `0x00000000`, `0xdeadbeef`, anything way outside the IRAM range `0x40000000-0x40400000`), the stack itself was smashed and the visible backtrace is garbage. Identify the offending task name from the `*** Currently running task:` line just above the panic header. Common Bitaxe culprits: `stratum_task` (deep JSON nesting), `http_server` (heavy on newer AxeOS UIs), `monitor_task` (stats logging). The fix is firmware-side — bump the task's stack in `sdkconfig` and recompile, or report upstream with the addr2line output and the task name and wait.

Tier 3: install the full ESP-IDF + ESP-Miner build environment, clone `bitaxeorg/ESP-Miner`, modify `sdkconfig` to raise the offending task's stack (`CONFIG_STRATUM_TASK_STACK_SIZE`, etc.), build with `idf.py build`, and flash your custom binary with `idf.py -p COM4 flash monitor`. If your patch resolves the panic, push it as a PR to `bitaxeorg/ESP-Miner`. This is where home miners stop being users and start being contributors. The Mining Hacker pleb-mining ethos in code form.

Stop DIY and ship to D-Central when (a) the latest stable AxeOS AND a downgrade both still produce reproducible panics, (b) decoded function names point at code that has no matching open issue (suggesting hardware-induced panic), (c) the panic is temperature-dependent (clean from cold, panics within 20-40 minutes of warm operation — solder fatigue under the ESP32-S3-WROOM module masquerading as a software bug), (d) `(IllegalInstruction)` with `EXCVADDR` in the IRAM range, (e) visible damage. Book at https://d-central.tech/services/asic-repair/. We stock salvaged-grade ESP32-S3-WROOM modules and bench fixtures for every Bitaxe variant. 3-7 business-day turnaround. Canada / US / international. D-Central pioneered the Bitaxe ecosystem — Mesh Stand, first heatsinks, full variant inventory.