LPC_GPIO_TypeDef learning notes

Now I am digging deeper on the GPIO part of the header file lpc11xx.h.  Now I know 
the following.

1. LPC_GPIO_TypeDef is a typedef struct.  In other words it is just a struct, not different that a typedef int is just an int.

2. What make things complicated is that there is a little struct inside the big struct, and there is something called a union.  I forgot what is a union.  So I need to google further.  The struct has members DATA and DIR.  Now I guess the weird string "->" should be like the dot which roughly member.

typedef struct
  {
  union 
    {
    ... 
    struct
      {
      }
    }
    ...
  }
  LPC_GPIO_TypeDef;


.END

Now let me look more closely the 3 define statements.

1. #define LPC_AHB_BASE          (0x50000000UL)

2. #define LPC_GPIO_BASE         (LPC_AHB_BASE  + 0x00000)

3. #define LPC_GPIO1             ((LPC_GPIO_TypeDef   *) LPC_GPIO1_BASE )

/*------------- General Purpose Input/Output (GPIO) --------------------------*/

typedef struct
{
  union {
    __IO uint32_t MASKED_ACCESS[4096];  /*!< Offset: 0x0000 (R/W) Port data Register for pins PIOn_0 to PIOn_11 */
    struct {
         uint32_t RESERVED0[4095];
    __IO uint32_t DATA;                 /*!< Offset: 0x3FFC (R/W) Port data Register */
    };
  };
       uint32_t RESERVED1[4096];
  __IO uint32_t DIR;                    /*!< Offset: 0x8000 (R/W)  Data direction Register */
  __IO uint32_t IS;                     /*!< Offset: 0x8004 (R/W)  Interrupt sense Register */
  __IO uint32_t IBE;                    /*!< Offset: 0x8008 (R/W)  Interrupt both edges Register */
  __IO uint32_t IEV;                    /*!< Offset: 0x800C (R/W)  Interrupt event Register */
  __IO uint32_t IE;                     /*!< Offset: 0x8010 (R/W)  Interrupt mask Register */
  __I  uint32_t RIS;                    /*!< Offset: 0x8014 (R/ )  Raw interrupt status Register */
  __I  uint32_t MIS;                    /*!< Offset: 0x8018 (R/ )  Masked interrupt status Register */
  __O  uint32_t IC;                     /*!< Offset: 0x801C ( /W)  Interrupt clear Register */
} LPC_GPIO_TypeDef;

.END