ZenOS RTOS

Scheduler & priorities

• Default: 16 priority slots.
• Configurable range: 2..256 slots.
• Priority 0 is reserved for idle and is not an application priority.
• At 256 slots, application priorities are 1..255; larger numeric values have higher priority.
• Ready selection uses a bitmap and per-priority ready queues; selection scans the configured priority range.
• Supporting 256 slots does not allocate a fixed 256-task table.

Timing

• Default kernel tick: 100 µs.
• Configurable range: 100..1000 µs, subject to the source validation rules.
• Periodic tasks use period_ticks and next_run_time as a scheduler release gate.
• Short microsecond delays are busy-wait operations; blocking delays yield the CPU.

Static resources

• Default stack request: 128 bytes; task creation enforces an effective minimum allocation of 256 bytes.
• Custom task stack sizes are available through os_task_create_st().
• The kernel task model uses statically sized task resources rather than a general-purpose task heap.
• Peak stack usage should be measured on the final target build.

IPC

• Events with ISR-safe signaling where provided.
• Mutexes with IPC ceiling behavior.
• Compile-time bounded FIFO queues.
• Counting semaphores.
• ISR-safe variants should be used from interrupt context where provided.

Monitoring

• Stack usage and watermark reporting.
• CPU usage reporting.
• Optional deadline monitoring.
• Optional TCB integrity checking.
• Fixed-size RAM error logging when enabled.

Configurable safety

• Software and hardware watchdog integration.
• MPU protection on suitable Cortex-M targets.
• RAM integrity testing.
• CRC-based integrity checking.
• Critical-section diagnostics.
• Safety target profiles perform compile-time configuration checks; they are not certification evidence.