Linux ARM (IMX6U) bare metal assembly LED driver experiment--driver writing

1. Initialization of i.MX6ULL

①、Enable clock

Enable clock. The seven registers CCGR0-CCGR6 control the enable of all peripheral clocks of i.MX6ULL. For simplicity, set all seven registers CCGR0-CCGR6 to 0xFFFFFFFF, which is equivalent to enabling all peripheral clocks.

CCGR0:

CCGR1:

CCGR2:

CCGR3:

CCGR4:

CCGR5:

CCGR6:

The assembly enables all peripheral clocks:

②、Configure GPIO_I003 PIN multiplexing as GPIO

Set bit3-0 of IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO03 to 0101, so that GPIO_IO03 is multiplexed as GPIO

Assembly implementation:

③、Configure the electrical properties of IOMUXC_SW_PAD_CTL_PAD_GPIO1_IO03

Set the electrical properties of register IOMUXC_SW_PAD_CTL_PAD_GPIO1_IO03, including slew rate, speed, drive capability, open drain, pull-up and pull-down, etc.

Assembly code implementation:

④. Configure GPIO function and set input and output

Set GPIO1_GDIR register bit3 to 1, that is, set it to output mode

Assembly implementation:

⑤、Set bit3 of GPIO_DR register, 1 means output high level, 0 means output low level

Assembly implementation:

The entire assembly code (.s file):

.global _start @Global label

_start:

    /*Enable all peripheral clocks*/

    LDR R0 , =0x020c4068 @CCGR0 

    LDR R1, =0xffffffff @To write data to CCGR0

    STR R1, [R0] @Write the value of R1 into R0

    LDR R0 , =0x020c406c @CCGR1

    STR R1 ,[R0]

    LDR R0 , =0x020c4070 @CCGR1

    STR R1 ,[R0]

    LDR R0 , =0x020c4074 @CCGR1

    STR R1 ,[R0]

    LDR R0 , =0x020c4078 @CCGR1

    STR R1 ,[R0]

    LDR R0 , =0x020c407c @CCGR1

    STR R1 ,[R0]

    LDR R0 , =0x020c4080 @CCGR1

    STR R1 ,[R0]

    /*Configure GPIO_I003 PIN multiplexing as GPIO

    * IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO03 = 0101 = 5

    * The address of IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO03 register is 0x020E_0068

    */

    LDR R0 , =0x020E0068 @IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO03

    LDR R1 , =0x5 @Data to be written

    STR R1 , [R0] @Write 5 to IOMUXC_SW_MUX_CTL_PAD_GPIO1_IO03

    /*Configure the electrical properties of IOMUXC_SW_PAD_CTL_PAD_GPIO1_IO03

    * The address of IOMUXC_SW_PAD_CTL_PAD_GPIO1_IO03 is 0x020E_02F4

    * bit0: 0 low rate

    * bit5-3: 110 R0/6 drive capability

    * bit7-6: 10 100MHz speed

    * bit11: 0 turns off open-circuit output

    * bit12: 1 enable pull/keeper

    * bit15-14: 00 100K pull-down

    * bit16: 0 turn off hys    

    * Write 0x10b0 to register IOMUXC_SW_PAD_CTL_PAD_GPIO1_IO03

    */

    LDR R0 , = 0x020E02F4

    LDR R1 , = 0x10b0

    STR R1 ,[R0]

    /*Set GPIO function

     * Set GPIO1_GDIR register Set GPIO1_GPIO03 as output

     *The address of register GPIO_GDIR is 0x0209C004

     * Set GPIO1_GDIR register bit3 to 1, which means GPIO1_GPIO03 is output

     */

    LDR R0 , = 0x0209C004

    LDR R1 , = 0x8

    STR R1 ,[R0]

    /*Turn on the LED, that is, set GPIO1_GPIO03 to 0 

     *GPIO1_DR register address is 0x0209C000

    */

    LDR R0 , = 0x0209C000

    LDR R1, =0

    STR R1 ,[R0]

loop:

    b loop