What does RESERVERD0 in Registers like USART1 in stm32f103 mean in stm32f10x.h header file? And how do I define a custom struct for the same?

Question

So recently I started bare-metal programming an stm32f103 device, and I was referring a builtin file "stm32f10x.h" in Keil uVision5, and I came across the TypeDef of USART struct it was like,

      typedef struct
      {
      __IO uint16_t SR;
      uint16_t  RESERVED0;
      __IO uint16_t DR;
      uint16_t  RESERVED1;
      __IO uint16_t BRR;
      uint16_t  RESERVED2;
      __IO uint16_t CR1;
      uint16_t  RESERVED3;
      __IO uint16_t CR2;
      uint16_t  RESERVED4;
      __IO uint16_t CR3;
      uint16_t  RESERVED5;
      __IO uint16_t GTPR;
      uint16_t  RESERVED6;
      } USART_TypeDef;

And I could not able to find any declaration or reference for these RESERVEDx registers. And if I want to define one custom struct for this register how do I do it? Thanks in advance:)

Answer 1

They are not RESERVEDx registers only higher word of the 32 bit register which should not be touched. Simply ignore them, do not touch them, do not think about them.