is anyone familiar with book programming embedded system

[liletian]

pin22_func_general

Hi Guys
Is anyone familiar with the book "programming embedded systems", I am confusing with page 49 in the book.
First they
#define LED_GREEN (0x00400000)
Then they
set one of the register vale to
GPIO_0_clear_REG = LED_GREEN;

Then they set up the control pin
#DEFINE PIN22_FUNC_GENERAL (oxFFFFCFFF)
CAN anyone explain why they define "PIN22_FUNC_GENERAL (oxFFFFCFFF)"?
I had no clue why they are doing this!
GPIO_O_FUNC_HI_REG &= PIN22_FUNC_GENERAL;


at last they
GPIO_O_DIRECTION_REG |= LED_GREEN


The definition of GPIO_0_clear_REG,GPIO_O_FUNC_HI_REG,GPIO_O_DIRECTION_REG are

GPIO_O_DIRECTION_REG =(*((unit32_t volatile *)ox40E0000C))
GPIO_0_clear_REG=(*((unit32_t volatile *)ox40E00024))
GPIO_O_FUNC_HI_REG=(*((unit32_t volatile *)ox40E00058))
Thanks a lot for your help

 

[sk321]

Configures GPIO pins for general I/O or alternate functionality.00 = GPIO pin is used as general-purpose I/O.
GPIO_O_FUNC_HI_REG &= PIN22_FUNC_GENERAL is used to configure GPIO22 as general-purpose I/O

 

[mezo]

you can see this link: