《嵌入式硬件（八）：基于IMX6ULL的点灯操作》

一、IMX6ULL启动代码

.global _start


_start:
	ldr pc, =_reset_handler
	ldr pc, =_undefine_handler
	ldr pc, =_svc_handler
	ldr pc, =_prefetch_abort_handler
	ldr pc, =_data_abort_handler
	ldr pc, =_reserved_handler
	ldr pc, =_irq_handler
	ldr pc, =_fiq_handler

_undefine_handler:
	ldr pc, =_undefine_handler

_svc_handler:
	ldr pc, =_svc_handler

_prefetch_abort_handler:
	ldr pc, =_prefetch_abort_handler

_data_abort_handler:
	ldr pc, =_data_abort_handler

_reserved_handler:
	ldr pc, =_reserved_handler

_irq_handler:
	ldr pc, =_irq_handler

_fiq_handler:
	ldr pc, =_fiq_handler

_reset_handler:
    mrs r0, cpsr
    bic r0, r0, #0x1F
    orr r0, r0, #0x12   //irq
    msr cpsr, r0

    ldr sp, =0x86000000	//起始地址80000000，ram大小为512mb（20000000）	80000000~A0000000-1

    mrs r0, cpsr
    bic r0, r0, #0x1F
    orr r0, r0, #0x1F   //system
    msr cpsr, r0   

    ldr sp, =0x84000000	//给irq分配的栈指针空间

二、点灯的步骤

                1）初始化时钟

                2）设置引脚功能复用（GPIO）

                3）引脚电气属性（功率、电阻）

                4）设置外设引脚的输入输出方向

                5）设置数据寄存器拉低/拉高电平

三、初始化系统时钟

                ARM内核为了低功耗，刚开始是全部关闭（通过cg门）

把这七个寄存器全部打开，值全部设置为默认值，初始化系统时钟

四、功能复用

        设置为gpio1

五、电气属性

        默认值就行，因为是输出

      六、外设引脚GDRI

                设置输入输出

七、数据寄存器DR

 八、点灯代码

        1.代码结构

bsp为各种.c.h文件，im6ull为内核文件，obj是生成文件的保存路径，project是主函数以及启动文件

2.bsp

        1)led.c

#include "led.h"
#include "fsl_iomuxc.h"
#include  "MCIMX6Y2.h"


void init_led(void)
{
    IOMUXC_SetPinMux(IOMUXC_GPIO1_IO03_GPIO1_IO03, 0);
    IOMUXC_SetPinConfig(IOMUXC_GPIO1_IO03_GPIO1_IO03, 0x10B0);
    GPIO1->GDIR |= (1 << 3);
}

void led_on(void)
{
    GPIO1->DR &= ~(1 << 3);
}

void led_off(void)
{
    GPIO1->DR |= (1 << 3);
}

void led_nor(void)
{
    GPIO1->DR ^= (1 << 3);
}

        2)led.h

#ifndef _LED_H_
#define _LED_H_

extern void init_led(void);
extern void led_on(void);
extern void led_off(void);
extern void led_nor(void);


#endif

3.project

        1)main.c

#include "MCIMX6Y2.h"
#include "fsl_iomuxc.h"
#include "led.h"


void enable_clocks(void)
{
    CCM->CCGR0 = 0xFFFFFFFF;
    CCM->CCGR1 = 0xFFFFFFFF;
    CCM->CCGR2 = 0xFFFFFFFF;
    CCM->CCGR3 = 0xFFFFFFFF;        
    CCM->CCGR4 = 0xFFFFFFFF;
    CCM->CCGR5 = 0xFFFFFFFF;
    CCM->CCGR6 = 0xFFFFFFFF;  
}

void delay(unsigned int n)
{
    while(n--);
}

int main(void)
{
    enable_clocks();
    init_led();
    while(1)
    {
        led_nor();
        delay(0xFFFFF);
    }
    return 0;
}

        2)start.S

.global _start


_start:
	ldr pc, =_reset_handler
	ldr pc, =_undefine_handler
	ldr pc, =_svc_handler
	ldr pc, =_prefetch_abort_handler
	ldr pc, =_data_abort_handler
	ldr pc, =_reserved_handler
	ldr pc, =_irq_handler
	ldr pc, =_fiq_handler

_undefine_handler:
	ldr pc, =_undefine_handler

_svc_handler:
	ldr pc, =_svc_handler

_prefetch_abort_handler:
	ldr pc, =_prefetch_abort_handler

_data_abort_handler:
	ldr pc, =_data_abort_handler

_reserved_handler:
	ldr pc, =_reserved_handler

_irq_handler:
	ldr pc, =_irq_handler

_fiq_handler:
	ldr pc, =_fiq_handler


_reset_handler:
    mrs r0, cpsr
    bic r0, r0, #0x1F
    orr r0, r0, #0x12   //irq
    msr cpsr, r0

    ldr sp, =0x80600000

    mrs r0, cpsr
    bic r0, r0, #0x1F
    orr r0, r0, #0x1F   //system
    msr cpsr, r0   

    ldr sp, =0x80400000
    bl _bss_clear
    b main

_bss_clear:
    ldr r0, =__bss_start
    ldr r2, =__bss_end
loop:
    mov r1, #0
    str r1, [r0]
    add r0, r0, #4
    cmp r0, r2
    blt loop
    bx lr

finished:
    b finished

4.Makefile

target = led

cross_compiler = arm-linux-gnueabihf-

cc = $(cross_compiler)gcc
ld = $(cross_compiler)ld
objcopy = $(cross_compiler)objcopy
objdump = $(cross_compiler)objdump

incdirs = bsp imx6ull
srcdirs = bsp project

include = $(patsubst %, -I%, $(incdirs))


cfiles = $(foreach dir, $(srcdirs), $(wildcard $(dir)/*.c))
sfiles = $(foreach dir, $(srcdirs), $(wildcard $(dir)/*.S))

cfilenodir = $(notdir $(cfiles))
sfilenodir = $(notdir $(sfiles))

cobjs = $(patsubst %, obj/%, $(cfilenodir:.c=.o))
sobjs = $(patsubst %, obj/%, $(sfilenodir:.S=.o))

objs = $(cobjs) $(sobjs)

VPATH = $(srcdirs)

$(target).bin : $(objs)
	$(ld) -Timx6ull.lds -o$(target).elf $^
	$(objcopy) -O binary -S -g $(target).elf $@
	$(objdump) -D $(target).elf > $(target).dis

$(sobjs) : obj/%.o : %.S
	@mkdir -p obj
	$(cc) -Wall -nostdlib -c $(include) -o $@ $<

$(cobjs) : obj/%.o : %.c
	@mkdir -p obj		
	$(cc) -Wall -nostdlib -c $(include) -o $@ $<

.PHONY : clean
clean:
	rm -rf $(objs) $(target).elf $(target).bin $(target).dis