bootloader-debug

A troubleshooting guide for embedded bootloaders, the small programs that start device firmware and manage firmware updates. It covers the handoff from the bootloader to the main application and the checks that decide which firmware image can run.

In plain words
What is it for?
Use it to investigate application jumps, vector-table and startup errors, image checks, firmware slots, OTA updates, rollback, boot selection, and recovery-mode problems.
Why use it?
It helps find why an update succeeds but the device will not start, or why the bootloader launches the wrong firmware. It encourages checking memory layout, image data, validation, and recovery information before changing or erasing boot areas.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/easyzoom/aix-skills/bootloader-debug
Any agent
npx skills add easyzoom/aix-skills --skill bootloader-debug
Clone the repo
git clone --depth 1 https://github.com/easyzoom/aix-skills

Made for: Claude Code, Codex.

Per session 35 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 868 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00035 $0.00868
Opus 5 $0.00017 $0.00434
Sonnet 5 $0.00007 $0.00174
Haiku 4.5 $0.00003 $0.00087

Measured 3d ago against content hash 94268c7931e0, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

bootloader-debug scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 3d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/bootloader-debug/SKILL.md · 103 lines

How it starts

The opening of the file, as written. The whole thing — 103 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Bootloader Debug

Overview

Use this skill to debug bootloader and application handoff problems without destroying recovery paths. Verify memory layout, image metadata, vector table, stack pointer, reset handler, validation, and rollback state before reflashing or erasing boot regions.

When To Use

Use this skill when:

  • A bootloader cannot start an application or jumps to the wrong image.
  • OTA/upgrade succeeds but the new firmware does not boot.
  • The issue involves image headers, checksums, signatures, slots, rollback, vector table relocation, or boot pins.
  • The user mentions MCUboot, U-Boot, vendor bootloader, IAP, DFU, app offset, or recovery mode.

Do not use this skill for ordinary application crashes after a confirmed clean handoff; use embedded-fault-debug. For MCUboot-specific slot/signing/swap issues, use mcuboot-integration. For OTA delivery pipeline issues, use ota-update-integration.

First Questions

Ask for:

  • Chip/board and bootloader type.
  • Memory map: bootloader, app slot, scratch, config, NVM, and backup areas.
  • Image format and validation: raw binary, HEX, signed image, checksum, metadata header.
  • Upgrade state: active slot, pending, confirmed, rollback, recovery, or unknown.
  • Logs from bootloader and application if available.
  • Whether recovery access still works.

Workflow

  1. Protect recovery. Do not erase bootloader, recovery slot, calibration, or persistent upgrade state without explicit approval.

  2. Confirm memory layout. Compare linker script, flash programming address, image header, and bootloader slot configuration.

  3. Validate handoff basics. For MCU apps, check initial SP and reset handler at the application offset. For Linux boot, check kernel, device tree, rootfs, and bootargs.

  4. Check image decision logic. Inspect version, checksum/signature, pending/confirmed flags, rollback counters, and slot priority.

  5. Trace the jump. Halt before handoff, inspect target SP/PC, vector table relocation, interrupts, clocks, caches, and peripheral state.

Read the full file on GitHub · 103 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 3d ago First seen · 103 lines · 35 tokens per session scan A 94268c7931e0

Subscribe to this mod's changes

bootloader-debug is a skill published in the GitHub repository easyzoom/aix-skills (31 stars, last pushed 1mo ago), licensed MIT. It adds 35 tokens to every session and 868 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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