lpc11xx.h reading notes

Now I am reading the lpc11xx.h, focusing on the gpio things.

// LPC11xx.h

// General Purpose Input/Output (GPIO)

typedef struct
{
  ...
  __IO uint32_t DATA;     
  ...
  __IO uint32_t DIR;      
  ...
} LPC_GPIO_TypeDef;


// Peripheral memory map   
                                                           
#define LPC_FLASH_BASE        (0x00000000UL)
#define LPC_RAM_BASE          (0x10000000UL)
#define LPC_APB0_BASE         (0x40000000UL)
#define LPC_AHB_BASE          (0x50000000UL)

// APB0 peripherals  
...

// AHB peripherals                                                            

#define LPC_GPIO_BASE         (LPC_AHB_BASE  + 0x00000)
#define LPC_GPIO0_BASE        (LPC_AHB_BASE  + 0x00000)
#define LPC_GPIO1_BASE        (LPC_AHB_BASE  + 0x10000)
#define LPC_GPIO2_BASE        (LPC_AHB_BASE  + 0x20000)
#define LPC_GPIO3_BASE        (LPC_AHB_BASE  + 0x30000)

Peripheral declaration

#define LPC_GPIO0             ((LPC_GPIO_TypeDef   *) LPC_GPIO0_BASE )
#define LPC_GPIO1             ((LPC_GPIO_TypeDef   *) LPC_GPIO1_BASE )
#define LPC_GPIO2             ((LPC_GPIO_TypeDef   *) LPC_GPIO2_BASE )
#define LPC_GPIO3             ((LPC_GPIO_TypeDef   *) LPC_GPIO3_BASE )

.END

Now let me think aloud. 

1.  LPC_GPIO_TypeDef is the type of a struct as defined.

2. #define LPC_GPIO0 is expanded as below.

LPC_GPIO_TypeDef *LPC_GPIO0_BASE


So similar to the declaration 

int *p 

where p is a pointer to an integer, 

LPC_GPIO0_BASE is a pointer to a LPC_GPIO_TypeDef structure.

But now I know I am very wrong.  LPC_GPIO_TypeDef *LPC_GPIO0_BASE is not a structure variable declaration.

The * is a derefencing operator here.

In other words, LPC_GPIO_TypeDef  *LPC_GPIO0_BASE means LPC_GPIO0 is the structure object at address LPC_GPIO0_BASE.

The LPC_GPIO_TypeDef prefix might be used as shortcut thing as described in the wikipedia.

Then I understand why I can use the following statement.

LPC_GPIO1->DATA &= ~(1 << pinNumber);


Here LPC_GPIO1 is the structure object, then of course the member can be assessed like LPC_GPIO1->DATA.

Now if I would like to pass pointer of the structure object LPC_GPIO1 as a function parameter, then the pointer should be

&LPC_GPIO1

This is indeed confusing.  I am only 80% sure that I am thinking correctly.

.END