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Re: Co-operative Multitasking Library For AVR Microcontrollers June 19, 2024 08:00PM |
For implementing cooperative multitasking on AVR microcontrollers like the ATtiny2313, you can follow a structured approach using timers and interrupt handling. Here’s a step-by-step outline to create a simple cooperative multitasking framework:
1. Timer Setup
Use one of the timers available on the ATtiny2313 (e.g., Timer/Counter1) to generate periodic interrupts. This timer will be used to create a system tick, which forms the basis for task scheduling.
2. Interrupt Service Routine (ISR)
Define an ISR for the timer interrupt. This ISR will be executed at regular intervals and will handle task switching and other system-level operations.
Example ISR structure:
ISR(TIMER1_COMPA_vect) {
// Update system time or perform other necessary tasks
// Switch tasks if needed (context switch)
}
In this ISR:
Update the system time or tick counter.
Perform context switching between tasks if necessary (switching tasks based on their states or priorities).
3. Task Management
Implement task management functions to handle tasks in your system. Each task should be defined as a function or a task control block (TC
structure containing necessary task information (like task function pointer, stack pointer, state, etc.).
Example task structure:
typedef struct {
void (*taskFunction)(void); // Pointer to task function
uint16_t period; // Execution period in ticks
uint16_t ticksToNextExecution; // Remaining ticks until next execution
// Add other parameters as needed
} TaskControlBlock;
TaskControlBlock tasks[NUM_TASKS]; // Array of task control blocks
4. Task Scheduler
Create a scheduler function that iterates through the task list and decides whether to execute each task based on its state and the current system time/tick.
Example scheduler:
void scheduler(void) {
for (int i = 0; i < NUM_TASKS; ++i) {
if (tasks.ticksToNextExecution == 0) {
tasks.taskFunction(); // Execute the task
tasks.ticksToNextExecution = tasks.period;
} else {
tasks.ticksToNextExecution--;
}
}
}
5. Main Loop
In your main() function or main loop, initialize the tasks, start the timer, and enter a loop where you continuously call the scheduler or wait for interrupts, depending on your design.
Example main loop:
int main(void) {
// Initialize tasks, timers, etc.
initTasks();
initTimer();
// Enable global interrupts
sei();
while (1) {
// Call scheduler or wait for interrupts
scheduler();
}
return 0;
}
Additional Considerations:
Stack Management: Ensure each task has sufficient stack space allocated.
Task Synchronization: Use synchronization techniques like semaphores or flags for inter-task communication if needed.
Interrupt Safety: Be mindful of interrupt safety when accessing shared resources from both tasks and ISRs.
By following these steps, you can implement a basic cooperative multitasking framework on the ATtiny2313 AVR microcontroller, allowing multiple tasks to run in a sequential manner based on a predefined scheduling algorithm. Adjustments may be necessary based on specific project requirements and system constraints.
1. Timer Setup
Use one of the timers available on the ATtiny2313 (e.g., Timer/Counter1) to generate periodic interrupts. This timer will be used to create a system tick, which forms the basis for task scheduling.
2. Interrupt Service Routine (ISR)
Define an ISR for the timer interrupt. This ISR will be executed at regular intervals and will handle task switching and other system-level operations.
Example ISR structure:
ISR(TIMER1_COMPA_vect) {
// Update system time or perform other necessary tasks
// Switch tasks if needed (context switch)
}
In this ISR:
Update the system time or tick counter.
Perform context switching between tasks if necessary (switching tasks based on their states or priorities).
3. Task Management
Implement task management functions to handle tasks in your system. Each task should be defined as a function or a task control block (TC
structure containing necessary task information (like task function pointer, stack pointer, state, etc.).
Example task structure:
typedef struct {
void (*taskFunction)(void); // Pointer to task function
uint16_t period; // Execution period in ticks
uint16_t ticksToNextExecution; // Remaining ticks until next execution
// Add other parameters as needed
} TaskControlBlock;
TaskControlBlock tasks[NUM_TASKS]; // Array of task control blocks
4. Task Scheduler
Create a scheduler function that iterates through the task list and decides whether to execute each task based on its state and the current system time/tick.
Example scheduler:
void scheduler(void) {
for (int i = 0; i < NUM_TASKS; ++i) {
if (tasks.ticksToNextExecution == 0) {
tasks.taskFunction(); // Execute the task
tasks.ticksToNextExecution = tasks.period;
} else {
tasks.ticksToNextExecution--;
}
}
}
5. Main Loop
In your main() function or main loop, initialize the tasks, start the timer, and enter a loop where you continuously call the scheduler or wait for interrupts, depending on your design.
Example main loop:
int main(void) {
// Initialize tasks, timers, etc.
initTasks();
initTimer();
// Enable global interrupts
sei();
while (1) {
// Call scheduler or wait for interrupts
scheduler();
}
return 0;
}
Additional Considerations:
Stack Management: Ensure each task has sufficient stack space allocated.
Task Synchronization: Use synchronization techniques like semaphores or flags for inter-task communication if needed.
Interrupt Safety: Be mindful of interrupt safety when accessing shared resources from both tasks and ISRs.
By following these steps, you can implement a basic cooperative multitasking framework on the ATtiny2313 AVR microcontroller, allowing multiple tasks to run in a sequential manner based on a predefined scheduling algorithm. Adjustments may be necessary based on specific project requirements and system constraints.