Hackaday log – Firmware architecture (Work in progress)

I am currently writing the firmware.
Time is limited at the moment and I am quite busy, so progress is steady but deliberately slow.

I am aligning the codebase with a new firmware “skeleton” I am developing:
https://github.com/Bertrand-selvasystems/firmware_skeleton_espidf

Architecture rules

Drivers (module_*.c) are self-contained

• No FreeRTOS includes
• No queues
• No event bits
• Clean C API only: init / read / write / deinit

Tasks (task_*.c) orchestrate hardware access through drivers
Tasks are the only place where the system:

• uses FreeRTOS primitives (queues, event groups, notifications)
• implements retry and delay logic
• sets, clears and waits on event bits
• manages health monitoring and fault handling

APIs (API_*.c) talk to tasks, not to hardware

• They provide intent-level functions
• They hide internal queues and events from the rest of the application

Configuration is split into two layers

• Frozen hardware configuration (system_cfg.*): wiring, addresses, frequencies (const, never modified)
• Runtime state: handles, flags, counters, queues, event groups

Layers and dependencies

app_main / initialization
→ API_* (facade, intent-level calls)
→ task_* (FreeRTOS actors, ownership and logic)
→ module_* (drivers, hardware access only)

Allowed dependencies

• module_* may depend only on ESP-IDF drivers (I2C, UART, GPIO, etc.), never on system_*
• task_* may depend on system_types, system_queues, system_state, system_faults and module_*
• API_* may depend on task-facing command queues and system_* but never on hardware

Design rationale

The goal is clean, stable firmware, especially by enforcing one service per critical hardware block.
This guarantees zero concurrent access to the same peripheral, even in unexpected edge cases, which is a major stability gain.

This point is absolutely central for a system designed to run unattended for five years, or close to it, such as a remote LoRa repeater deployed in the field.

At this stage, I have implemented:

• the I2C service
• the PCA (I/O expander) service

The current work-in-progress code is available here:
https://github.com/Bertrand-selvasystems/loratube_firmware

There is still a lot to do, but the foundation is now in place. 

The LEDs are blinking, which is usually a good sign.