TQ210 —— s5pv210 lowlevel_init.S分析（uboot第一阶段）

/*

 * Memory Setup stuff - taken from blob memsetup.S

 *

 * Copyright (C) 1999 2000 2001 Erik Mouw (J.A.K.Mouw@its.tudelft.nl) and

 *                     Jan-Derk Bakker (J.D.Bakker@its.tudelft.nl)

 *

 * Modified for the Samsung SMDK2410 by

 * (C) Copyright 2002

 * David Mueller, ELSOFT AG,

 *

 * See file CREDITS for list of people who contributed to this

 * project.

 *

 * This program is free software; you can redistribute it and/or

 * modify it under the terms of the GNU General Public License as

 * published by the Free Software Foundation; either version 2 of

 * the License, or (at your option) any later version.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 59 Temple Place, Suite 330, Boston,

 * MA 02111-1307 USA

 */

#include

#include

#include

#include "tq210_val.h"

@ 讲start.S的时候已经说过这个TEXT_BASE了

_TEXT_BASE:

.word TEXT_BASE

.globl lowlevel_init

lowlevel_init:

push {lr}   @ 将上一个函数的返回地址压入栈中

/* check reset status  */ 

@ 检查复位标志，如果是睡眠唤醒，跳过接下来的初始化

ldr r0, =(ELFIN_CLOCK_POWER_BASE+RST_STAT_OFFSET) @ 跳转到目的地Reset Control Register的地址传送给r0 Address = 0xE010_A000 =0xE010_0000+0xA000

ldr r1, [r0]  @ 将存储器地址为 R0(内存储的值) 的字数据读入寄存器 R1

bic r1, r1, #0xfff6ffff   @将r1与0xfff6ffff的反码按位进行与运算（既和0xfff6ffff进行与非运算），并写入r1；结合上一步，可知，这一步的作用是16和19bit置一，其他位清零

cmp r1, #0x10000  @ 判断16bit是不是等于1

beq wakeup_reset_pre  @ 如果是从睡眠状态唤醒，就跳转到wakeup_reset_pre，既跳过接下来的初始化

    cmp r1, #0x80000    @ 判断是不是从深度空闲（Deep-IDLE）状态唤醒

beq wakeup_reset_from_didle   @ 如果是，就跳转到wakeup_reset_from_didle

/* IO Retention release */

ldr r0, =(ELFIN_CLOCK_POWER_BASE + OTHERS_OFFSET)  @ 将跳转目的地址MISC Register的地址传送给r0   Address = 0xE010_E000 =0xE010_0000+0xE000

ldr r1, [r0]  @ 将存储器地址为 R0(内存储的值) 的字数据读入寄存器 R1

ldr r2, =IO_RET_REL  @将IO_RET_REL（ ((1 << 31) | (1 << 29) | (1 << 28)) ）存入r2

    orr r1, r1, r2  @ 将r1和r2的值进行或运算，结果存入r1

str r1, [r0]  @ 将r1的值写入以r0内的值为地址的内存空间

/* Disable Watchdog */

@ 关闭看门狗

ldr r0, =ELFIN_WATCHDOG_BASE /* 0xE2700000 */

mov r1, #0

str r1, [r0]

/* SRAM(2MB) init for SMDKC110 */

/* GPJ1 SROM_ADDR_16to21 */

@ 配置sram引脚，16位数据宽度，22位地址宽度

ldr r0, =ELFIN_GPIO_BASE

ldr r1, [r0, #GPJ1CON_OFFSET]

bic r1, r1, #0xFFFFFF

ldr r2, =0x444444

orr r1, r1, r2

str r1, [r0, #GPJ1CON_OFFSET]

ldr r1, [r0, #GPJ1PUD_OFFSET]

ldr r2, =0x3ff

bic r1, r1, r2

str r1, [r0, #GPJ1PUD_OFFSET]

/* GPJ4 SROM_ADDR_16to21 */

ldr r1, [r0, #GPJ4CON_OFFSET]

bic r1, r1, #(0xf<<16)

ldr r2, =(0x4<<16)

orr r1, r1, r2

str r1, [r0, #GPJ4CON_OFFSET]

ldr r1, [r0, #GPJ4PUD_OFFSET]

ldr r2, =(0x3<<8)

bic r1, r1, r2

str r1, [r0, #GPJ4PUD_OFFSET]

/* CS0 - 16bit sram, enable nBE, Byte base address */

ldr r0, =ELFIN_SROM_BASE /* 0xE8000000 */

mov r1, #0x1

str r1, [r0]

/* PS_HOLD pin(GPH0_0) set to high */

@ 设置PMIC（Power Management IC）控制引脚，既电源管理ic引脚（基于I2C）

ldr r0, =(ELFIN_CLOCK_POWER_BASE + PS_HOLD_CONTROL_OFFSET)

ldr r1, [r0]

orr r1, r1, #0x300

orr r1, r1, #0x1

str r1, [r0]

/* when we already run in ram, we don't need to relocate U-Boot.

* and actually, memory controller must be configured before U-Boot

* is running in ram.

*/

/*下面的代码事实上只是判断pc和_TEXT_BASE(0X23e00000)的最高两位是否相同*/

     /* 根据s5pv210的数据手册可知，首先，系统会运行固化在irom的BL0，紧接着会从外部nand

      * 或sdcard等设备读取前16K的BL1代码到IRAM中的0xD0020000处。然后从0xD0020010处运行（因为前16byte是校验和的值）

      * BL1的作用是初始化DRAM，拷贝BL2到DRAM中_TEXT_BASE(0X23e00000)处，然后跳到DRAM中运行

      * 因此可以通过最高两位来判断代码是在哪里运行

      * 同时可知，当代码已经就在DRAM中运行时，就必须跳过DRAM的初始化

     */

ldr r0, =0xff000fff

bic r1, pc, r0 /* r0 <- current base addr of code */

ldr r2, _TEXT_BASE /* r1 <- original base addr in ram */

bic r2, r2, r0 /* r0 <- current base addr of code */

cmp     r1, r2                  /* compare r0, r1                  */

beq     1f /* r0 == r1 then skip sdram init   */

/* init PMIC chip */

#ifdef CONFIG_TQ210_IIC_PM_CHIP

bl PMIC_InitIp

#endif

/* init system clock */

@ 时钟初始化 PLL初始化，要想看懂此汇编，请查看datsheet中，clk control章节

bl system_clock_init

/* Memory initialize */

@ 内存初始化

bl mem_ctrl_asm_init

1:

/* for UART */

@ 串口初始化，要看懂此汇编, 请查看datsheet中, 请查看串口章节

bl uart_asm_init

bl tzpc_init

@ 这段不执行

#if defined(CONFIG_ONENAND)

bl onenandcon_init

#endif

    @ nand初始化

#if defined(CONFIG_NAND)

/* simple init for NAND */

bl nand_asm_init

#endif

/* check reset status  */

ldr r0, =(ELFIN_CLOCK_POWER_BASE+RST_STAT_OFFSET)

ldr r1, [r0]

bic r1, r1, #0xfffeffff

cmp r1, #0x10000

beq wakeup_reset_pre

/* ABB disable */

ldr r0, =0xE010C300

orr r1, r1, #(0x1<<23)

str r1, [r0]

/* Print 'K' */

ldr r0, =ELFIN_UART_CONSOLE_BASE

ldr r1, =0x4b4b4b4b

str r1, [r0, #UTXH_OFFSET]

pop {pc} @ 返回到start.S

wakeup_reset_from_didle: @ 从深度睡眠中唤醒

/* Wait when APLL is locked */

ldr r0, =ELFIN_CLOCK_POWER_BASE

lockloop:

ldr r1, [r0, #APLL_CON0_OFFSET]

and r1, r1, #(1<<29)

cmp r1, #(1<<29)

bne lockloop @ 这里使用循环

beq exit_wakeup

wakeup_reset_pre:

mrc p15, 0, r1, c1, c0, 1 @Read CP15 Auxiliary control register

and r1, r1, #0x80000000 @Check L2RD is disable or not

cmp r1, #0x80000000

bne wakeup_reset @if L2RD is not disable jump to wakeup_reset 

bl disable_l2cache

bl v7_flush_dcache_all

/* L2 cache enable at sleep.S of kernel

* bl enable_l2cache 

*/

#ifdef CONFIG_TQ210

bl enable_l2cache

#endif

wakeup_reset:

/* init system clock */

bl system_clock_init

bl mem_ctrl_asm_init

bl tzpc_init

#if defined(CONFIG_ONENAND)

bl onenandcon_init

#endif

#if defined(CONFIG_NAND)

bl nand_asm_init

#endif

exit_wakeup:

/*Load return address and jump to kernel*/

ldr r0, =(INF_REG_BASE+INF_REG0_OFFSET)

ldr r1, [r0] /* r1 = physical address of s5pc110_cpu_resume function*/

mov pc, r1 /*Jump to kernel */

nop

nop

/*

 * system_clock_init: Initialize core clock and bus clock.

 * void system_clock_init(void)

 */

system_clock_init:

   /* 这一段的作用是将Clock Source Control Registers值清空

    * 具体的作用是将VPLL_SEL、EPLL_SEL、MPLL_SEL和APLL_SEL的时钟源设置为FINVPLL，将MUX_MSYS_SEL、MUX_DSYS_SEL和MUX_PSYS_SEL时钟源设置为SCLKMPLL

    * 将ONENAND_SEL时钟源设置为HCLK_PSYS

    * 为什么这样设置，因为未设置 PLL 和各种分频系数之前，我们不能使用 PLL，为了保险起见，暂时直接使用频率较低

    * 的外接的 24MHz 晶振，待设置好 PLL 和分频系数后再重新设置各种时钟开关

    */

ldr r0, =ELFIN_CLOCK_POWER_BASE @0xe0100000

/* Set Mux to FIN */

ldr r1, =0x0

str r1, [r0, #CLK_SRC0_OFFSET]

ldr r1, =APLL_LOCKTIME_VAL   @将APLL_LOCKTIME_VAL(0x2cf)装入r1

str r1, [r0, #APLL_LOCK_OFFSET]  @将r1内的值装入地址为（r0内的值+CLK_SRC0_OFFSET = 0xe0100000）的内存，即设置APLL的锁定周期

    /*

* A PLL requires locking period when input frequency is changed or frequency division (multiplication) values are

     * changed.PLL_LOCK register specifies this locking period, which is based on PLL’s source clock. During this

     * period, output will be low state

    */

/* Disable PLL */

#if defined(CONFIG_CHECK_MPLL_LOCK)

retryloop:

#endif

ldr r1, =0x0

str r1, [r0, #APLL_CON0_OFFSET]  @ 将APLL控制寄存器的值清空，这个寄存器的第31位置零关闭APLL 25-16bit配置MDIV的分频 

@ 13-8bit配置PDIV的分频 2-0bit配置SDIV的分频

ldr r1, =0x0

str r1, [r0, #MPLL_CON_OFFSET]   @ 配置MPLL

ldr r1, =0x0

str r1, [r0, #MPLL_CON_OFFSET]   @ 重复配置MPLL，确保MPLL配置成功

ldr    r1, [r0, #CLK_DIV0_OFFSET] @ Clock Divider Control Register(0xe0100300)

ldr r2, =CLK_DIV0_MASK             @ CLK_DIV0_MASK(0x7fffffff)

bic r1, r1, r2                     @ 首先清零

ldr r2, =CLK_DIV0_VAL              @ CLK_DIV0_VAL

orr r1, r1, r2

str r1, [r0, #CLK_DIV0_OFFSET]

    /*

    *CLK_DIV0_VAL = ((0<    *   |(3<    *#define APLL_RATIO         0

    *#define A2M_RATIO          4

    *#define HCLK_MSYS_RATIO    8

    *#define PCLK_MSYS_RATIO    12

    *#define HCLK_DSYS_RATIO    16

    *#define PCLK_DSYS_RATIO    20

    *#define HCLK_PSYS_RATIO    24

    *#define PCLK_PSYS_RATIO    28

    */

ldr r1, =APLL_VAL

str r1, [r0, #APLL_CON0_OFFSET]

ldr r1, =MPLL_VAL

str r1, [r0, #MPLL_CON_OFFSET]

ldr r1, =VPLL_VAL

str r1, [r0, #VPLL_CON_OFFSET]

#if defined(CONFIG_EVT1)

ldr r1, =AFC_ON

str r1, [r0, #APLL_CON1_OFFSET]

#endif

mov r1, #0x10000

1: subs r1, r1, #1    @ 延时 将r1-1的值存入r1

bne 1b                @ 如果运算结果不等零（即CPSR寄存器标志位Z不等于一），退回到前面标签“1”处执行  当 CPSR 寄存器中的 Z 

                          @ 条件码置位时（即前面的计算结果为零），则顺序执行(即运行接下来的：ldr   r1, [r0, #CLK_SRC0_OFFSET])