Taking Keil MDK development environment as an example, an unsigned 32-bit plastic data will have many representations: 1, unsigned int 32 (C language standard expression method) 2, uint32 _ t; 3. u32 All three ways are expressing the same meaning, but why did the developers of ST make such a mess? There are many other expressions that you may find strange and difficult to understand, such as _IO int32_t, which is equivalent to vs32 (you are also strange), but also equivalent to volatile int32_t and volatile signed int 32. This last expression is a standard expression in C language, which is confusing enough for beginners.