STM32 timer input capture points

The one using is stm32f103rct6.

I am currently writing a program that uses a single timer to capture 4-channel PWM waves. I have to change the detection edge in the interrupt function and manually calculate the PWM frequency and pulse width by manually recording the captured values.

There are many related programs on the Internet, but when I was writing them, I encountered a very insignificant problem for beginners, which caused the results to be wrong:

As shown in the figure, I am using TIM4_CH1. Because I saw that other structures were defined by themselves before use, I defined an object 'TIM4_Type' in the 'TIM_TypeDef' structure and then found that the result was wrong.

After careful analysis, I found that this structure already has an object instance in stm32f10x.h: TIM4. And the location of this TIM4 is exactly where those registers are located, and the object 'TIM4_Type' I defined myself is in the user memory area, so no matter how I operate 'TIM4_Type', I can't get the correct result.

Later, I looked at the official manual of V3.5 and found that those 'xxx_TypeDef' structures all have their own object declarations in stm32f10x.h and their own specific memory addresses. In other words, this type of structure does not need to be defined by yourself, while other types do not have specific memory addresses, so they need to be defined by themselves before they can be operated.