《嵌入式硬件（十二）：基于IMX6ULL的时钟操作》

一、时钟基本概念

PLL：phase locked loop 倍频

Prescaler：预分频器

PFD：相位分数分频器（可升可降）

7个pll,pll2、pll3一共有8个pfd

二、时钟原理

1.核心版原理图

2.时钟树

2，3，4，为分频因子展开所占二进制位数，值要加一，因为要作为分母使用

参数配置如下

3.ARM PLL配置方法

1）CCSR寄存器

第一二四步

2）ARM_PLL寄存器

第三步

配置pll

3）CCM_CACRR寄存器

第三步

设置分频因子

4.PLL2 配置（528）

5.AHB_CLK_ROOT（绿色的线）

1）CBCMR

2)CBCDR

6.PERCLK_CLK_ROOT

1） CSCMR1（修改一分频）

7.IPG_CLK_ROOT

AHB_CLK_ROOT（绿色的线）设置好后，通过CBCDR进行二分频

三、代码

结构不变

1.bsp

1)clock.c

cs 复制代码

#include "clock.h"
#include "led.h"
#include "MCIMX6Y2.h" 
#include "core_ca7.h"

void init_clock(void)
{
    unsigned int t;
    CCM->CCSR &= ~(1 << 8);
    CCM->CCSR |= (1 << 2);
    t = CCM_ANALOG->PLL_ARM;
    t &= (~(3 << 14));
    t |= ((1 << 13));
    t &= (~(0x7f << 0));
    t |= (88 <<0);
    CCM_ANALOG->PLL_ARM = t;
    CCM->CACRR |= (1 << 0);
    CCM->CCSR &= (~(1 << 2));

    t = CCM_ANALOG->PFD_528;
    t &= (~(0x3f << 0) | (0x3f << 8) | (0x3f << 16) | (0x3f << 24));
    t &= (~((1 << 7) | (1 << 15) | (1 << 23) | (1 <<31)));
    t |= ((27 < 0) | (16 << 8) | (24 << 16) | (32 << 24));
    CCM_ANALOG->PFD_528 = t;

    t = CCM_ANALOG->PFD_480;
    t &= (~(0x3f << 0) | (0x3f << 8) | (0x3f << 16) | (0x3f << 24));
    t &= (~((1 << 7) | (1 << 15) | (1 << 23) | (1 <<31)));
    t |= ((12 < 0) | (16 << 8) | (17 << 16) | (19 << 24));
    CCM_ANALOG->PFD_480 = t;

    t = CCM->CBCMR;
    t &= ~(3 << 18);
    t |= (1 << 18);
    CCM->CBCMR = t;

    CCM->CBCDR &= ~(1 << 25);
    t = CCM->CBCDR;
    t &= ~((7 << 10) | 3 << 8);
    t |= ((2 << 10) | (1 << 8)); 
    CCM->CBCDR = t;

    CCM->CSCMR1 &= ~(1 << 6);
    CCM->CSCMR1 &= ~(0x3f << 0);

    enable_clocks();
}

2)clock.h

cs 复制代码

#ifndef _CLOCK_H_
#define _CLOCK_H_

extern void init_clock(void);

#endif

2.project

1)main.c

cs 复制代码

#include "beep.h"
#include "led.h"
#include "key.h"
#include "MCIMX6Y2.h" 
#include "core_ca7.h"
#include "gpio.h"
#include "interrupt.h"
#include "clock.h"


int main(void)
{
    init_clock();
    system_interrupt_init();
    init_led();
    init_beep();
    //init_key();   
    while(1)
    {
        led_nor();
        delay(0x0FFFFF);
    }
    return 0;
}

2)start.S

cs 复制代码

.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:
 subs lr, lr, #4

    mrc p15, 4, r1, c15, c0, 0
    add r1, r1, #0x2000
    ldr r0, [r1, #0x0C]

    stmfd sp!, {r0-r12, lr}

    stmfd sp!, {r0, r1}

	cps #0x1f
	stmfd sp!, {lr}

    bl system_interrupt_handler

	ldmfd sp!, {lr}
    ldmfd sp!, {r0, r1}
    str r0, [r1, #0x10]


    ldmfd sp!, {r0-r12, pc}^

_fiq_handler:
	ldr pc, =_fiq_handler

_reset_handler:
    //mrs r0, cpsr
    //bic r0, r0, #0x1F
    //orr r0, r0, #0x12   //irq
	//bic r0, r0, #(1 << 7)
    //msr cpsr, r0
	cps #0x12

    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   
	cps #0x1f
	cpsie i

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


	bl _bss_clear
	b main

_enable_icahce:
	mrc p15, 0, r0, c1, c0, 0
	bic r0, r0, #(1 << 13)
	orr r0, r0, #(1 << 12)
	mcr p15, 0, r0, c1, c0, 0
	bx lr

_set_vbar:
	ldr r0, =0x87800000
	mcr p15, 0, r0, c12, c0, 0
	bx lr


_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