A possible cause and solution of "stuck" main thread of RT thread

Write it at the front

The current bare metal programs can no longer meet the code structure requirements of embedded robots , Because the system of an embedded robot is very huge , By Perception algorithm , Decision algorithm and control algorithm Other components , This does not include some programs that need to be connected . Huge code needs A chip level operating system to shield the impact of hardware on the upper Algorithm , At the same time, it provides API, Help the upper algorithm call the lower hardware , Therefore, a chip level operating system is very important , and RT-Thread It is a domestic chip level operating system , And my course just involves the system , So I'm going to write a series of blogs to record all kinds of problems in the process of learning this operating system , I hope I can bring you some help ~  

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Problem phenomenon

This semester we are taking embedded courses , Learned a new lightweight operating system ——RT-Thread( Hereinafter referred to as rtt), This is a domestic operating system , The characteristic of this operating system is Only the thread , No process , If we want to use this system, we only need to operate the corresponding thread , Then the way we use this system well is very simple , We just need Realize the coordination work between various threads That's all right. .     Get down to business , Before I learn this rtt I have a problem , That's it When I am main Functional while(1) Nothing in it , When running , The whole chip went down , Code as shown

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Reasons and solutions

The detour we took

  At the beginning, I thought the reason was in my whole project main Threads have a high priority , Other threads Is the lowest priority ( What I set up here is 25), When scheduling threads High priority threads will be scheduled first ,main Thread is the highest priority thread in my system , And it is in hurry in vain A thread of , So that is This main Threads are always occupying system resources , No other thread can be scheduled , Therefore, there is a phenomenon similar to system downtime .   At this point, I have to talk about our picture rtt The state flow diagram of thread scheduling of the system

In ordinary operating system , The flow between these States is relatively easy to understand , But in rtt in , It is different from other operating systems , I have already mentioned this before , That's it It has no process Of this thing , So in rtt Operating system , Ready state = Running state . That is to say... In the picture 2 The cycle represented by the circle is equivalent .    however , So there's a problem , Because if you follow my logic , Not just hurry in vain main Thread while(1) There will be system downtime when , Even if the main Thread while(1) The task program is added , Then our whole rtt The system also depends on the system Scheduling mechanism of process ( High priority threads must be scheduled first ) To call repeatedly main In the thread while(1) Tasks inside , Similarly, other threads will not be called , That's not gonna work , So I went to rtt Search the official website of , Finally, the mystery behind this problem is solved .  

See light suddenly

First, let's rtt System Define some concepts   Let's take the following code segment as an example  

void thread_entry(void* paramenter) {
    /*  Wait for the event to happen  */
    /*  Service events 、 To deal with  */ 
}

Thread ready / function

This code is the entity function of the thread , that rtt How will the system execute this program at that time ？ Let me draw an image to explain to you

If this thread High priority Words ,rtt The system will always execute this thread , It will not execute other threads , Because the thread will enter be ready state , And because this thread has Highest priority , So after entering the thread scheduling pool, it will be scheduled to run again , Get into function state , But in rtt  in , actually ( In the process of implementation ) Thread does not exist running state , Ready state and running state are equivalent , But it is more convenient to understand the mechanism according to the above .  

Thread hanging

  rtt The official website has a relatively detailed , clear Description of , I made a move here , Invasion and deletion

The important thing in this paragraph is this sentence , Threads do not participate in scheduling , That is, no matter how high the priority of the thread is , He will not enter the thread scheduling pool , According to the description in the table , The conditions that cause the thread to hang are 2 individual  

1. 1. Resource not available
2. 2. Threads actively delay for a period of time

solve the problem

main A thread is a special thread , So he must also meet rtt System management thread mechanism .   Then our problem is well explained . When main Thread while(1) The program in the loop does not Resource unavailability occurs perhaps Thread active delay operation when , The thread will always be in function / be ready Stage , And because in my program ,main Thread has the highest priority , So my main Threads have been occupying system resources , Caused the illusion of system downtime . But if I was main Thread while(1) Insert... In the loop A delay procedure ,main The thread will enter Pending state , Give up system resources , So that other threads have a chance to be scheduled , Make the system run stably .