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Uboot's GPIO is quite simple, which is a three-tier structure. Respectively are: 1, the top interface layer, which only defines the general interface, and is not responsible for the implementation, the implementation is based on the specific chip to achieve.

2. In the middle interface implementation layer, the GPIO of the specific board is used to implement the interface of the top layer.

3. The implementation layer of the bottom specific chip GPIO.

Now make a specific analysis:

Top interface layer

Int gpio_request (unsigned gpio, const char * label); / / apply for GPIO resources

Int gpio_free (unsigned gpio); / / release the requested GPIO resources

Int gpio_direction_input (unsigned gpio); / / set GPIO to input mode

Int gpio_direction_output (unsigned gpio, int value); / / set GPIO to output mode

Int gpio_get_value (unsigned gpio); / / get the value of GPIO

Int gpio_set_value (unsigned gpio, int value); / / set the value of GPIO

Note: unsigned gpio is a logical number, although it has a certain relationship with the actual physical GPIO address, but it is not the actual physical GPIO address.

Intermediate interface implementation layer:

Use the GPIO of the specific chip to realize its top-level interface

Int gpio_request (unsigned gpio, const char * label)

{

Return 0

}

Int gpio_free (unsigned gpio)

{

Return 0

}

Int gpio_direction_input (unsigned gpio)

{

Sunxi_gpio_set_cfgpin (gpio, SUNXI_GPIO_INPUT)

Return sunxi_gpio_input (gpio)

}

Int gpio_direction_output (unsigned gpio, int value)

{

Sunxi_gpio_set_cfgpin (gpio, SUNXI_GPIO_OUTPUT)

Return sunxi_gpio_output (gpio, value)

}

Int gpio_get_value (unsigned gpio)

{

Return sunxi_gpio_input (gpio)

}

Int gpio_set_value (unsigned gpio, int value)

{

Return sunxi_gpio_output (gpio, value)

}

The implementation layer of the underlying specific chip GPIO:

In the implementation, it uses a little trick, its purpose is to put the physical register of GPIO into the structure, thus translating the physical address operation into the data structure operation.

The implementation is as follows:

Cast the SUNXI_PIO_BASE to a sunxi_gpio_reg * pointer.

# define SUNXI_PIO_BASE 0x01c20800

Struct sunxi_gpio {

U32 cfg [4]

U32 dat

U32 drv [2]

U32 pull [2]

}

Struct sunxi_gpio_int {

U32 cfg [3]

U32 ctl

U32 sta

U32 deb

}

Struct sunxi_gpio_reg {

Struct sunxi_gpio gpio_bank [9]

U8 res [0xbc]

Struct sunxi_gpio_int gpio_int

}

The idea that we implement the GPIO operation of a specific chip is:

Use the logical symbol unsigned gpio to manipulate the relevant registers through the SUNXI_PIO_BASE cast to the pointer of the sunxi_gpio_reg * pointer.

However, if the logical symbol unsigned gpio is to be converted to a pointer of the sunxi_gpio_reg * pointer by SUNXI_PIO_BASE to manipulate the related registers, we must solve the problem of how to find the specified register among the many registers and find the specified related bits on the register.

That is, offset in gpio---- > bank- > bank

This mapping relationship is related to the specific chip.

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