Firment: A Rust Coding Agent That Closes the Embedded Loop — Code, Build, Flash, Monitor, and Analyze the ELF in One Conversation

#ai #rust #embedded

Hi everyone,

I've been working on an open-source coding agent called Firment, written in Rust, and I'd like to share it here and get feedback from embedded developers.

The idea isn't to build another general AI chat assistant, but to explore a more reliable workflow for firmware development. Most coding agents can generate code, but I kept hitting the same problems on embedded projects:

They don't understand MCU-specific context well (clock domains, DMA channel mapping, cache coherency, and so on)
They may overwrite files after the code has already changed
They don't verify whether the generated firmware actually builds
Long debugging sessions lose important context

So Firment focuses on the execution layer rather than just code generation.

Safety / reliability:

Concurrent-change detection — files are re-checked before every write (content-addressed with SHA-256, compare-and-swap style), plus line-level "hashline" anchors for large files
Transactional editing with rollback
Diff-first approval before applying changes (edits echo a unified diff)
Persistent edit ledger and /undo
Verify gates — when a build command is configured (e.g. cmake --build build), the harness refuses to declare completion until it passes
Workspace sandboxing, tool schema validation, and a dangerous-command guard (rm / format / git reset --hard etc. are blocked unless explicitly allowed)

Embedded toolchain (the part I've spent the most time on recently):

periph_init — generates peripheral-init skeletons (UART/GPIO/I2C/SPI/TIM/ADC, STM32 HAL style) instead of writing init code from scratch
elf_analyze — reads flash/RAM usage, function sizes, and real stack depth from -fstack-usage .su files
monitor — serial monitor with per-line timestamps and baud autodetect
build / flash / run — CMake/Make/Keil build commands and probe-rs flashing, wired into the agent loop

Embedded knowledge base:

The built-in index currently covers STM32F1, F4, G0, G4, H7, ESP32, and ESP32-S3. It uses a layered approach: read the family index → load quick-reference cheatsheets → follow pointers to official manual sections for deeper detail (manual ingestion is planned, not shipped). The goal is to avoid stuffing huge datasheets into the context window and instead let the agent pull in only what's relevant.

The current agent supports Anthropic- and OpenAI-compatible APIs (DeepSeek / Qwen / GLM / Ollama), tool calling, planning mode, symbol indexing, and context management.

Example workflow:

User: Add UART DMA receive support to this STM32 project

Firment: infer the MCU family from the project (.ioc / build config) → load UART + DMA knowledge → inspect the project structure → modify files transactionally → run the build/verify gate.

It's still evolving (v0.5.0) and I'd really appreciate feedback from people who work on real firmware projects. Especially: