freertos-patterns

FreeRTOS Patterns for ESP32 and RP2040

Use this skill for real concurrency problems on ESP32 or RP2040. Keep the main flow focused and load the detailed reference that matches the user's exact problem.

Resources

• references/patterns-task-creation.md - task lifecycle, priorities, stack sizing, and task startup
• references/patterns-queues.md - inter-task communication with queues
• references/patterns-synchronization.md - mutexes, semaphores, critical sections, and ISR coordination
• references/patterns-memory.md - stack sizing, heap checks, and monitoring
• references/patterns-advanced.md - watchdogs, notifications, event groups, timers, and affinity
• assets/workflow.mmd - architecture overview

When to Use

Use this skill when the request includes:

• multiple concurrent jobs on ESP32
• task priorities or preemption
• queue, semaphore, mutex, or notification design
• RP2040 setup1 and loop1 multicore coordination
• watchdog-safe long-running behavior
• debugging race conditions, stack overflows, or deadlocks

Do not use this skill when:

• the target is UNO or another single-core board
• a simple millis() scheduler solves the problem
• the request is only about one blocking loop with no concurrency requirement

Workflow

For a control system's task/resource ownership, action timing or deadline budget, start with realtime-control-design. Return here for the actual RTOS primitive. Native ESP-IDF uses its own port's stack units, affinity and critical section rules; do not copy an Arduino/RP2040 example into another framework without checking the selected SDK.

1. Confirm the target platform first:
   • ESP32 -> FreeRTOS task model
   • RP2040 -> dual-core coordination model
2. Identify the dominant problem:
   • task startup -> open patterns-task-creation.md
   • communication -> open patterns-queues.md
   • shared data or ISR signaling -> open patterns-synchronization.md
   • stack or heap risk -> open patterns-memory.md
   • watchdogs, notifications, timers, or affinity -> open patterns-advanced.md
3. Solve one synchronization boundary at a time. Avoid mixing queue, mutex, and notification advice unless the design truly needs all of them.
4. Keep board-specific details explicit. ESP32 FreeRTOS guidance and RP2040 multicore guidance are not interchangeable.

Core Rules

• Prefer the smallest concurrency primitive that solves the problem.
• Protect shared state explicitly. "Probably safe" is not safe.
• Use vTaskDelay() or event-driven blocking on ESP32, never delay() inside a task.
• Budget stack size deliberately and verify it with runtime evidence.
• For RP2040, define core ownership clearly before sharing data.

Verification

• Confirm each task or core has a single clear responsibility.
• Check queue depth, notification flow, or mutex coverage against the concrete data path.
• For ESP32, inspect stack headroom with uxTaskGetStackHighWaterMark() where the task size is uncertain.
• Verify the sketch can keep making progress without deadlock or busy waiting.
• If an ISR is involved, verify the synchronization primitive is ISR-safe for that platform.

Common Failure Modes

• undersized task stack
• delay() used inside a FreeRTOS task
• unprotected shared data
• deadlock from inconsistent lock order
• RP2040 core startup assumptions without mutex or ownership discipline

Integration

• Combine with arduino-code-generator when the user needs a full sketch rather than design guidance.
• Combine with circuit-debugger only after the concurrency design looks sound and a hardware timing issue still remains.
• Combine with mermaid-diagram-generator when the concurrency design needs a task, queue, or event-flow diagram.

Shared Output Contract

Use the shared Arduino skill contract: state assumptions, required tools and versions, implementation steps, tests/evidence by proof stage, known limitations, and recovery/security notes.