Overview

Purpose

The Sequencer utility is a simple alternative to a real-time operating system for less complex application cases. However, it does not provide all the services of a full operating system.

Key Features

The main features of Sequencer are:

  • Task creation: Initializes a task and makes it callable by the Sequencer’s internal scheduler.

  • Task enable: Enables a task from another task or an interrupt so that the scheduler can run it.

  • Task pause/resume: Pauses or resumes a task execution from the scheduler’s viewpoint, independently of whether the task is enabled or not.

  • Idle task: Calls an optional hook when no task is runnable to manage idle entry.

Architecture

The following diagram illustrates the software components of the Sequencer module. It shows the interactions between the user application, the core layer, the optional configuration layer, the system support (CMSIS), and the hardware components.

@startuml top to bottom direction skinparam linetype ortho <style> componentDiagram { arrow { FontSize 8 } } </style> title Sequencer Architecture Overview package "Application" { component APP as "User Application\n(tasks + main loop)" } package "Sequencer" { component CORE as "Core Layer\n(cooperative scheduler + APIs)" component CONF as "Optional Configuration\n(seq_user_conf.h)" #DAE8FC } package "System" { component CMSIS as "CMSIS-Core" [STM32_HW] } APP --> CORE : run / task control CORE --> CONF : user configuration CORE --> CMSIS : core services CMSIS --> STM32_HW : core register access @enduml

Component Structure

Core ( sequencer.c / sequencer.h): Replaces heavier scheduling solutions with a lean cooperative engine. It simplifies task management by running each task until it finishes. It reduces the risk of lockups by encouraging short task bodies, enables controlled waiting through a single event pause mechanism, and offers optional idle and task hooks for power management and monitoring.

Optional Configuration ( seq_user_conf.h): Adjusts the scheduler at build time through a small configuration layer. It sets limits such as the number of tasks and priority levels, defines how critical sections and idle handling work to match the target platform, and allows small utility macros (memory fill, etc.) to be replaced when needed. All platform-specific tweaks stay outside the core so that the main logic remains clean and portable. Safe defaults are applied automatically when no custom settings are provided.

Modules and Files

The following diagram shows the Sequencer module and its associated files:

@startuml Sequencer_modules skinparam componentStyle rectangle skinparam defaultFontName Courier skinparam ArrowColor #2A4B8D skinparam ArrowFontSize 10 skinparam RectangleBackgroundColor #FFFFFF skinparam RectangleBorderColor #2A4B8D skinparam Shadowing false skinparam linetype ortho title Sequencer Modules Overview package "Application" { component APP as "Application" } package "Sequencer" { component SEQ_C as "sequencer.c" component SEQ_H as "sequencer.h" component SEQ_USER_CONF as "seq_user_conf.h" #DAE8FC } APP --> SEQ_C SEQ_C ..> SEQ_H : include SEQ_C ..> SEQ_USER_CONF : include (if ``SEQ_USER_CONFIG`` is defined) @enduml

Configuration Table

The following table lists the configuration defines for the Sequencer module:

Config Defines

Where

Description

SEQ_USER_CONFIG

Preprocessor environment

Enable custom user configuration ( seq_user_conf.h)