New explanation of the source code of the MCU infrared remote control decoding routine

This is the third time that I have changed the infrared remote control decoding routine. The first version used the external interrupt of the 51 microcontroller directly and then added a delay to collect the length of the high and low levels to determine the boot code and bit 1 and bit 0. I don't know where I saw this at the beginning. This method is too misleading. If you want to use this idea to transplant it to stm32, you should stop as soon as possible. Is this advanced processor like stm32 only used for infrared remote control decoding? No, there will definitely be more advanced tasks waiting for it to process. External interrupt plus delay can improve the response speed of the remote control, but in fact this method is very resource-intensive. When the cpu is processing other urgent tasks, a key suddenly comes to interrupt the process and occupy the process. After testing, a key code of the remote control takes 50-90ms, which is not a small time for the microcontroller. Therefore, the external interrupt + timer can be combined for decoding.
The external interrupt turns on the rising and falling edges to trigger at the same time. In this way, after two triggers, we calculate the high or low comment time to see if it is accurate.
The state machine, that is, the state change idea, can be used for decoding. The boot code and user code are divided into two parts for decoding. The high level and low level are divided into two parts for decoding.
Because the difference between bit 1 and bit 0 is the different time of high level, that is, bit 0 _|—| bit 1
  _|——| The time of low level of both
is the same, and the high level behind is long for 1 and short for 0. This feature makes it particularly easy to solve. Please refer to the previous article, http://www.xiaovdiy.cn/?post=138
Source code is provided
         if(EXTI_GetITStatus(EXTI_Line12)!= RESET)
         {
          if(RDATA()==0)//Indicates that a falling edge has arrived
          {
           
        TIM_Cmd(TIM4, ENABLE);
                 if(lead_flg==0)//Indicates that it is the first time to receive the lead code
                 {
                            TIM_SetCounter(TIM4,0);//TIM4->CNT=0; （1）
            lead_flg=1;
                   }
                   else if(lead_flg==2)
                   {
                 ir_cnt= TIM_GetCounter(TIM4);    
            TIM_SetCounter(TIM4,0);
                            lead_flg=3;
                            if((ir_cnt<70)||(ir_cnt>90))//The test shows that it is 79 or 80
                            {
                              lead_flg=0; //Out of range, exit
              return 0;
              
                            }
                   }
                   else if(lead_flg==3)//Get the high level time
                   {
                            ir_cnt= TIM_GetCounter(TIM4);    
                            TIM_SetCounter(TIM4,0);
                            //Receive 3 bytes 24-bit code
                high_cnt++;//Add to 24 bits, 1 byte every 8 timesif
                     (high_cnt<=8)
                                     {
                                               user_code[0]>>=1;
                                     }
                if(high_cnt<=16)
                                     {
                                               user_code[1]>>=1;
                                               }
                if(high_cnt<=24)
                                     {
                                               user_code[2]>>=1;
                                     }
                     if((ir_cnt>35)&&(ir_cnt<45))//We think it is bit '1'
                                     {
                         if(high_cnt<=8)
                                               {
                                                        user_code[0]|=0x80;
 
                                               }
                    if(high_cnt<=16)
                                               {
                                                        user_code[1]|=0x80;
                                               }
                    if(high_cnt<=24)
                                               {
                                                        user_code[2]|=0x80;}
                                         }
                           if(high_cnt>24)//Acceptance completed
                                     {
                                               lead_flg = 0;
                                               high_cnt = 0;
                                               REM_FLG = 1;//Acquisition completed, clear flag
 
                                               TIM_Cmd( TIM4,DISABLE);
                                     }
                          
 
                   }
 
          }
          else if(RDATA()!=0)//It means that this is the first time to receive the high level of the lead code
          {
       if(lead_flg==0)
       {
       return 0;
       }
       else if(lead_flg==1)//We only need to accept one low level 2
            {
                            ir_cnt= TIM_GetCounter(TIM4);
                            TIM_SetCounter(TIM4,0);
                                     lead_flg=2;
                            if((ir_cnt<70)||(ir_cnt>90))
                            {
                              lead_flg=0;//Not what we want, exit
              return 0;
               
                            }
 
                   }
                   else if(lead_flg==3)//Non-lead code entry interrupt rising edge triggered
                   {  
                       ir_cnt= TIM_GetCounter(TIM4);
                            TIM_SetCounter(TIM4,0);
                                    
                            if((ir_cnt<8)||(ir_cnt>20))//Test data is ir_cnt =9 10 stable value
                            {
                              lead_flg=0;
              return 0;//Not what we want, exit
               
                            }
                           
 
                   }
          }
 
         }