SE4Binome2025-2

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Objectif

L'objectif du projet est de concevoir un pico-ordinateur complet, intégrant :

  • Une carte mère basée sue le microcontrôleur AT90USB1286

Une partie logicielle permettant l'éxecution de de commandes telles que ls, cp ou mv

Shield Arduino

Une première étape du projet a consisté à développer un shield pour Aduino uno, servant de plateforme de test et de développement pour les cartes filles SPI.

Fonctionalités:

  • Connexion de 5 périphériques SPI via des cartes filles.
  • Gestion des signaux Reset et Interruption.
  • Ajout d'une mémoire externe carte micro-SD via un connecteur Molex 10431.
  • Adaptation des niveaux logiques (5V a 3,3V) grâce à la puce 74LV125.

Ce shield joue le rôle de plateforme de développement temporaire, en attendant la carte mère du pico-ordinateur.

Schématique et routage

Schema shield arduino.jpg

Objectif

Schema shield arduino


Routage shield arduino


Carte mère

Schématique

\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{listings}
\usepackage{xcolor}
\usepackage{graphicx}
\usepackage{hyperref}
\usepackage{geometry}
\geometry{a4paper, margin=1in}

\title{Dual-LED Binary Clock Firmware: RTOS Architecture Report}
\author{}
\date{}

\begin{document}

\maketitle

\section{System Architecture Overview}

The firmware implements a cooperative real-time operating system (RTOS) for ATmega328p microcontrollers, featuring a memory-optimized kernel with round-robin scheduling capabilities.

\subsection{Component Hierarchy}

\begin{verbatim}
firmware/
├── kernel/
│   ├── kernel.[ch]      - Core kernel management
│   ├── scheduler.[ch]   - Task scheduler implementation
│   ├── task.[ch]        - Task control block system
│   └── config.h         - Resource configuration
└── main.c              - Application layer
\end{verbatim}

\section{Core Kernel Mechanisms}

\subsection{Task Management System}

The kernel implements a static task control block (TCB) architecture:

\begin{lstlisting}[language=C]
typedef struct task_control_block {
    void (*function)(void*);    // Task entry point
    void* arg;                  // Task parameters
    uint8_t* stack_base;        // Stack memory (96 bytes)
    task_state_t state;         // Current task state
    uint16_t sleep_ticks;       // Sleep countdown
    uint8_t priority;          // Execution priority (0-3)
    char name[TASK_NAME_LENGTH]; // Task identifier
} task_t;
\end{lstlisting}

\subsection{Task State Transitions}

The system implements a finite state machine for task management:

\[
\text{TASK\_READY} \rightleftharpoons \text{TASK\_RUNNING} \rightarrow \text{TASK\_SLEEPING} \rightarrow \text{TASK\_READY}
\]

\subsection{Task Creation Protocol}

\begin{lstlisting}[language=C]
int8_t task_create(const char* name, void (*function)(void*), 
                   void* arg, uint8_t priority, uint8_t* stack_buffer)
\end{lstlisting}

\textbf{Creation Constraints:}
\begin{itemize}
\item Maximum task count: $MAX\_TASKS = 4$
\item Stack size: $STACK\_SIZE = 96$ bytes
\item Priority levels: $\{PRIORITY\_IDLE, PRIORITY\_LOW, PRIORITY\_MEDIUM, PRIORITY\_HIGH\}$
\end{itemize}

\section{Scheduling Algorithm}

\subsection{Round-Robin Implementation}

The scheduler employs a circular search algorithm to find the next executable task:

\begin{lstlisting}[language=C]
static uint8_t get_next_task(void) {
    uint8_t next_task = (current_task_id + 1) % MAX_TASKS;
    for (uint8_t i = 0; i < MAX_TASKS; i++) {
        if (is_task_valid(next_task) && 
            task_table[next_task].state == TASK_READY) {
            return next_task;
        }
        next_task = (next_task + 1) % MAX_TASKS;
    }
    return current_task_id;
}
\end{lstlisting}

\subsection{Execution Flow}

The main scheduler loop follows this sequence:

\begin{enumerate}
\item Enter critical section (disable interrupts)
\item Execute current task function
\item Calculate next task ID using round-robin
\item Leave critical section (enable interrupts)
\item Apply 1ms CPU delay to prevent overload
\end{enumerate}

\section{Memory Management}

\subsection{Resource Allocation}

The system employs static memory allocation for predictable resource usage:

\[
\begin{align*}
\text{Total RAM for stacks} &= MAX\_TASKS \times STACK\_SIZE = 4 \times 96 = 384 \text{ bytes} \\
\text{TCB memory footprint} &= MAX\_TASKS \times sizeof(task\_t) \approx 112 \text{ bytes} \\
\text{Global variables} &\approx 20 \text{ bytes} \\
\text{Total estimated usage} &\approx 516 \text{ bytes}
\end{align*}
\]

\subsection{Configuration Parameters}

\begin{lstlisting}[language=C]
#define MAX_TASKS 4           // Maximum concurrent tasks
#define STACK_SIZE 96         // Bytes per task stack
#define TICK_FREQUENCY 100    // Hz - scheduler frequency
#define TASK_NAME_LENGTH 8    // Maximum task name characters
\end{lstlisting}

\section{Interrupt and Critical Section Management}

\subsection{Atomic Operation Protection}

The kernel implements nested critical sections to protect shared resources:

\begin{lstlisting}[language=C]
void enter_critical_section(void) {
    cli();                    // Disable interrupts
    critical_nesting++;       // Track nesting depth
}

void leave_critical_section(void) {
    if (critical_nesting > 0) critical_nesting--;
    if (critical_nesting == 0) sei();  // Re-enable interrupts
}
\end{lstlisting}

\subsection{Timer Interrupt Configuration}

The system timer generates 100Hz interrupts for tick management:

\[
OCR1A = \frac{F\_CPU}{Prescaler \times Frequency} - 1 = \frac{16,000,000}{64 \times 100} - 1 = 2499
\]

\begin{lstlisting}[language=C]
// Timer1 configuration for 100Hz
TCCR1A = 0;
TCCR1B = (1 << WGM12) | (1 << CS11) | (1 << CS10);
OCR1A = 2499;
TIMSK1 |= (1 << OCIE1A);
\end{lstlisting}

\section{Sleep and Timing Mechanisms}

\subsection{Tick-Based Sleep System}

Tasks can suspend execution for precise durations using system ticks:

\[
\text{sleep\_ticks} = \left\lceil \frac{\text{milliseconds}}{10} \right\rceil
\]

\begin{lstlisting}[language=C]
void task_sleep(uint16_t ticks) {
    enter_critical_section();
    task_table[current_task_id].sleep_ticks = ticks;
    task_table[current_task_id].state = TASK_SLEEPING;
    leave_critical_section();
    schedule();
}
\end{lstlisting}

\subsection{Tick Update Algorithm}

The interrupt service routine manages sleeping tasks:

\begin{lstlisting}[language=C]
ISR(TIMER1_COMPA_vect) {
    system_ticks++;
    for (uint8_t i = 0; i < MAX_TASKS; i++) {
        if (task_table[i].state == TASK_SLEEPING && 
            task_table[i].sleep_ticks > 0) {
            task_table[i].sleep_ticks--;
            if (task_table[i].sleep_ticks == 0) {
                task_table[i].state = TASK_READY;
            }
        }
    }
}
\end{lstlisting}

\section{System Initialization Sequence}

\subsection{Boot Process}

\begin{enumerate}
\item \textbf{Memory Zeroing}: Clear task table and global variables
\item \textbf{Timer Configuration}: Setup 100Hz interrupt timer
\item \textbf{Idle Task Creation}: Initialize fallback task with lowest priority
\item \textbf{Interrupt Enable}: Start scheduler tick generation
\item \textbf{Task Validation}: Mark all created tasks as READY state
\end{enumerate}

\section{Error Handling and Robustness}

\subsection{Boundary Condition Management}

\begin{itemize}
\item \textbf{Task Validation}: All task executions verify function pointer validity
\item \textbf{Sleep Sanitization}: Zero-tick sleep requests default to 1 tick
\item \textbf{Circular Search}: Scheduler handles empty task tables gracefully
\item \textbf{Nesting Safety}: Critical sections properly handle nested calls
\end{itemize}

\subsection{Recovery Mechanisms}

\begin{lstlisting}[language=C]
static uint8_t is_task_valid(uint8_t task_id) {
    return (task_id < MAX_TASKS && task_table[task_id].function != NULL);
}
\end{lstlisting}

\section{Performance Characteristics}

\subsection{Computational Complexity}

\begin{table}[h]
\centering
\begin{tabular}{|l|l|l|}
\hline
\textbf{Operation} & \textbf{Time Complexity} & \textbf{Space Complexity} \\
\hline
Task Creation & $O(n)$ & $O(1)$ \\
Task Scheduling & $O(n)$ & $O(1)$ \\
Sleep Update & $O(n)$ & $O(1)$ \\
Context Switch & $O(1)$ & $O(1)$ \\
\hline
\end{tabular}
\caption{Algorithm Complexity Analysis}
\end{table}

\subsection{Memory Efficiency}

The system achieves high memory efficiency through:
\begin{itemize}
\item Static allocation eliminating heap fragmentation
\item Fixed-size arrays for predictable memory usage
\item Stack sharing between kernel and application
\item Minimal TCB overhead (28 bytes per task)
\end{itemize}

\section{Build System Integration}

\subsection{Compilation Configuration}

\begin{lstlisting}[language=make]
MCU = atmega328p
F_CPU = 16000000UL
CFLAGS = -mmcu=$(MCU) -DF_CPU=$(F_CPU) -Os -Wall -std=c99
\end{lstlisting}

\subsection{Memory Section Allocation}

\[
\begin{align*}
\text{Program Memory} &= \text{.text} + \text{.data} \\
\text{RAM Usage} &= \text{.data} + \text{.bss} + \text{Stack}
\end{align*}
\]

\end{document}
Schéma carte mère du pico ordinateur
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