[basic course of flight control development 2] crazy shell · open source formation UAV - timer (LED flight information light and indicator light flash)

COCOFLY course
—— Crazy shell · Unmanned aerial vehicle (uav) · series
Timer （LED Flight information light 、 The indicator flashes ）

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One 、 About timer
  The timer has a timing function , Similar to life “ alarm clock ”, You can use a timer to generate accurate timing time , Used to delay or process some real-time events .
  STM32 Series of timers are divided into basic timers 、 Universal timer 、 Advanced control timer . The latter includes all the functions of the former . Usually ,STM32 Advanced timer yes TIM1、TIM8, The general timer is TIM2、TIM3、TIM4、TIM5, The basic timer is TIM6、TIM7.
  And the main core of flight control STM32F103CBT6 Then there are 4 road 16 Bit timers are advanced timers TIM1、 Universal timer TIM2、TIM3 as well as TIM4.

Two 、 Timer register
  STM32F103 There are many registers related to timers , Here we will only talk about a few important registers .
  （1）TIMx_CR1： Enable register , Switch of the lowest control register , As shown in the figure below ：

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  TIM_CR1 The register mainly configures the cycle count of the timer 、 Enable, etc , for example CEN Position as 1 Is enable counting , by 0 Is to turn off counting .
  （2）TIMx_DIER： Timer interrupt enable register , The switch of the lowest control event update interrupt , As shown in the figure below ：

 

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  The main function of this register is to configure the timer, which is the interrupt enable bit of the timer , The main use is UIE position ,UIE by 1 Is to enable interruption , by 0 Close interrupt .
  TIMx_PSC： Timer clock division register , As shown in the figure below ：

 

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  This register is responsible for dividing the timer clock , Then output to the counter ,PSC[15:0] Is the frequency division coefficient .
  （4）TIMx_ARR： The timer automatically reloads the register , As shown in the figure below ：

 

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  ARR[15:0] For automatic reload value , When the timer uses up counting , The count is equal to ARR when , Generate an update event ; When the timer is counting down , In the beginning ARR The value of is assigned to the count value , The count value is reduced downward to 0 when , Generate an update event , Once again ARR The value of is assigned to the count value , Count down for a new round .
  （5）TIMx_SR： Status register , Mark the current events related to the timer / Whether the interruption occurs , We only use the flag bit of the lowest bit indicating the interruption of event update , As shown in the figure below ：

 

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  This register is mainly used to view the update interrupt flag bit of the timer , When the count overflows or underflows ,UIF The bit will be set to 1, Mark the completion of one count .

 

3、 ... and 、 Timer experiment
  The experiment in this section is mainly aimed at GPIO Periodically light the flight information light and signal light of the UAV , Deform it , Use a universal timer TIM3 Periodically light and turn off the flight information lights and signal lights of the UAV at precise timing .
  It is also known from the schematic diagram that the flight information lights of the UAV are connected together NPN triode Q1 On , And the base of the triode is connected to the single chip microcomputer PA8 On ; Two signal lights are connected to PC13 and PC14 On .

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  About GPIO This part of the driver code can be inherited and retained , The difference is that you need to add timer initialization and configure timer interrupt , The idea of writing code is shown in the following table .

 

 

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  Follow the code idea , Write code （ By calling the official library ） As shown in the figure below GPIO Related driver code ：

 

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  Complete the configuration GPIO after , That is to configure the timer , our STM32 It's external 8MHz Crystal vibrating , The main frequency is 72MHz First, let's take a look at the clock tree , As shown in the figure below .

 

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  The timer is mounted on APB1 Under the clock bus （ From the manual ）, It can be seen from the clock tree APB1 The clock frequency used for the timer is not divided 72MHz, Divide the frequency register according to the timer clock （TIMx_PSC） And the timer automatically reloads the register （TIMx_ARR） The relationship between , We can draw , Timing time ：
Tout=((arr+1)*(psc+1))/Ft    s
  among Tout Is the fixed time unit s,arr Is the initial value of the automatic reload register ,psc Is the frequency division coefficient ,Ft by APB The main frequency of , That is to say 72MHz. Then it's time 1s Then just put arr Set to load value 9999,psc Set to 7199 that will do , namely ：
Tout=((9999+1)*(7199+1))/72000000
=10000*7200/72000000
=72000000/72000000
=1s
  So you can get the timer initialization code, as shown in the following figure .

 

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  After the configuration is completed 1s The cycle enters a timer interrupt , In the timer interrupt, the flight information light and indicator light of the UAV GPIO The port can be flipped , Light up periodically , The code is shown in the following figure .

 

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  Write the code and save 、 compile 、 download , Then you can see the flight control LED The pilot light and the cycle of the traffic lights under the four propellers 1S flashing , As shown in the figure below .

 

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