Source: https://blog.csdn.net/twx11213030422 Embedded Miscellaneous Layout
What is a Framework?
A programming framework is similar to a file outline or template. Writing a program is akin to writing an article; without an outline or template, it can be quite cumbersome.
Why Have a Framework?
To save time and reduce errors. For a specific type of program, the code structure and logic are often the same, with many similarities or commonalities. We can extract these common elements to form a fixed programming framework, allowing us to reuse this framework when developing new programs of the same type.
This significantly improves our development efficiency, and since this framework is publicly used and maintained, it makes the code logic less prone to errors.
Components of Embedded Systems
Embedded control systems are generally composed of “normal tasks” and “interrupt tasks”.
-
• Normal tasks: Tasks that do not have high time response requirements or are executed periodically;
-
• Interrupt tasks: Tasks that require immediate processing due to high time response requirements;
Common Frameworks
1. Polling without Interrupts
Description: All tasks are executed in sequence. To reduce the overall system response time, there are two methods:
-
1. Avoid using blocking delay functions in tasks;
-
2. If a task cannot be completed in one go, it should be broken down into smaller tasks, executing one small task in a loop until completion. Both methods will consume memory, and what could have been handled by local variables now must be managed with static or global variables.
Advantages: The program execution flow is simple and clear;
Disadvantages: Modifying system functionality is very inconvenient, and if the number of tasks increases, it will affect the overall system response time, leading to system lag;
Pseudocode Implementation:
int main(void)
{
while(1)
{
doSomething_1(); // Task 1
doSomething_2(); // Task 2
doSomething_3(); // Task 3
/* Other various tasks */
}
return 0;
}2. Only Interrupts
Description: In a system with “only interrupts”, the main function’s loop does not perform any operations.
Advantages: Can respond in real-time to exceptional tasks (events).
Disadvantages: Interrupt resources are limited, and when there are too many tasks, responses may be delayed.
Pseudocode Implementation:
int main(void)
{
while(1)
{
;
}
}
/* Interrupt Service Routine 1 */
void ISR1_IRQHandler(void)
{
doSomething_1();
}
/* Interrupt Service Routine 2 */
void ISR2_IRQHandler(void)
{
doSomething_2();
}3. Variants of the Only Interrupt Framework
Description: Uses a state machine mechanism to execute tasks. The interrupt function sets the state of the state machine, while the main function’s loop executes different tasks based on the state value. This does not truly belong to the only interrupt form.
int main(void)
{
while(1)
{
if(flag_1)
{
doSomething_1();
}
if(flag_2)
{
doSomething_2();
}
if(flag_3)
{
doSomething_3();
}
/* Other various tasks */
}
return 0;
}
/********* Interrupt Service Routine 1 ************/
void ISR1_IRQHandler(void)
{
flag_1 = ~flag_1;
}
/********* Interrupt Service Routine 2 ************/
void ISR2_IRQHandler(void)
{
flag_2 = ~flag_2;
}
/********* Interrupt Service Routine 3 ************/
void ISR3_IRQHandler(void)
{
flag_3 = ~flag_3;
}4. Polling with Interrupts
Description: Some periodic tasks are executed in the main function’s loop.
Advantages: Efficient resource utilization, separating regular tasks from urgent tasks.
Disadvantages: The program structure and logic are relatively complex, requiring significant effort in task allocation and collaboration.
Pseudocode Implementation:
int main(void)
{
while(1)
{
if(flag_1)
{
doSomething_1();
}
if(flag_2)
{
doSomething_2();
}
if(flag_3)
{
doSomething_3();
}
/* Other various tasks */
}
return 0;
}
/********* Timer Interrupt Service Routine ************/
void ISR1_IRQHandler(void)
{
}5. Polling with Interrupts – Virtual Timer
Description: Uses different “virtual timer” timing to call different tasks. When the timer’s timing expires, it executes a callback function or calls a task function.
This is very suitable for periodic tasks, and interrupts can handle external sudden events. This ensures real-time performance, but care should be taken to avoid using blocking delays. Generally, the time base for virtual timers is 1ms.
Advantages: The time intervals for tasks can be controlled relatively accurately, and the overall system’s real-time performance is good due to the use of interrupts.
Disadvantages: The execution time of tasks cannot be controlled, and if the execution time of a timed task is too long, it will affect the timing accuracy of the virtual timer.
Virtual timer implementation code:
https://codeload.github.com/0x1abin/MultiTimer/zip/master
6. Non-preemptive Real-Time Operating System
Description: There are no priority distinctions between tasks; each task is executed sequentially. However, the execution time of tasks is strictly controlled by the operating system. Even if a task is not completed, it will be suspended when the time slice expires.
Advantages: There is no need to worry about reducing delays in tasks; we can focus on business logic.
Disadvantages: Tasks are on the same level, which may prevent some tasks from being processed urgently.
Pseudocode Implementation:
https://blog.csdn.net/twx11213030422/article/details/104637273
7. Preemptive Real-Time Operating System
Description: Each task is in a “dead loop” and has a priority. High-priority tasks can interrupt low-priority tasks, similar to interrupts. This results in excellent real-time performance, and each task is also controlled by time slices, meaning their execution times are predictable. It also supports interrupts to respond to urgent events.
Advantages: Real-time response; engineers can focus on implementing business logic.
Disadvantages: Requires porting and has certain hardware resource requirements for microcontrollers.
Common Preemptive Real-Time Operating Systems: Keil RTX, FreeRTOS, uCosII/III, etc.
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