u-boot-2014.10移植第8天----深入分析代码(三)

硬件平台:tq2440

开发环境:Ubuntu-3.11

u-boot版本:2014.10

本文允许转载,请注明出处:http://blog.csdn.net/fulinus


接着第七天的代码分析,下面是cpu_init_crit的代码段,同样位于文件arch/arm/cpu/arm920t/start.S中:

/*
 *************************************************************************
 *  
 * CPU_init_critical registers
 *
 * setup important registers
 * setup memory timing
 *
 *************************************************************************
 */


#ifndef CONFIG_SKIP_LOWLEVEL_INIT
cpu_init_crit:
    /*
     * flush v4 I/D caches
     */
    mov r0, #0
    mcr p15, 0, r0, c7, c7, 0   /* flush v3/v4 cache */
    mcr p15, 0, r0, c8, c7, 0   /* flush v4 TLB */

    /*
     * disable MMU stuff and caches
     */
    mrc p15, 0, r0, c1, c0, 0
    bic r0, r0, #0x00002300 @ clear bits 13, 9:8 (--V- --RS)
    bic r0, r0, #0x00000087 @ clear bits 7, 2:0 (B--- -CAM)
    orr r0, r0, #0x00000002 @ set bit 2 (A) Align
    orr r0, r0, #0x00001000 @ set bit 12 (I) I-Cache
    mcr p15, 0, r0, c1, c0, 0

    /*
     * before relocating, we have to setup RAM timing
     * because memory timing is board-dependend, you will
     * find a lowlevel_init.S in your board directory.
     */
    mov ip, lr

    bl  lowlevel_init

    mov lr, ip
    mov pc, lr
#endif /* CONFIG_SKIP_LOWLEVEL_INIT */


u-boot-2014.10移植第8天----深入分析代码(三)_第1张图片
mcr/mrc指令:http://blog.csdn.net/oyzhizhong/article/details/6967932

这段代码详见:http://blog.chinaunix.net/uid-11251862-id-2888834.html

协处理器说明: http://blog.csdn.net/skyflying2012/article/details/25823967

    mov ip, lr //保存返回地址

    bl  lowlevel_init

    mov lr, ip //还原返回地址
    mov pc, lr //子函数返回

进入lowlevel_init子函数,该函数在board/samsung/smdk2410/lowlevel_init.S:

.globl lowlevel_init
lowlevel_init:
    /* memory control configuration */
    /* make r0 relative the current location so that it */
    /* reads SMRDATA out of FLASH rather than memory ! */
    ldr     r0, =SMRDATA   //r0保存SMRDATA的位置;
    ldr r1, =CONFIG_SYS_TEXT_BASE //在文件include/configs/smdk2410.h中定义为#define CONFIG_SYS_TEXT_BASE    0x0
    sub r0, r0, r1  // r0 = r0 - r1  = r0 - 0
    ldr r1, =BWSCON /* Bus Width Status Controller */  //#define BWSCON  0x48000000
    add     r2, r0, #13*4  //r2 = r0 +13*4  13个寄存器,如图:

u-boot-2014.10移植第8天----深入分析代码(三)_第2张图片
0:
    ldr     r3, [r0], #4   // r3 = *r0   ,    r0 = r0 + 4 ; 第一次循环时r3 = (0+(B1_BWSCON<<4)+(B2_BWSCON<<8)+(B3_BWSCON<<12)+(B4_BWSCON<<16)+(B5_BWSCON<<20)+(B6_BWSCON<<24)+(B7_BWSCON<<28))
    str     r3, [r1], #4  // *r1 = r3   ,    r1 + 4;   第一次循环时将上面r3的值写到BWSCON寄存器中。
    cmp     r2, r0   //判断r0与r2是否相等 , 13个寄存器
    bne     0b     //不相等就跳到0处,b不是向后跳。


    /* everything is fine now */
    mov pc, lr   //返回


    .ltorg
/* the literal pools origin */


SMRDATA:
    .word (0+(B1_BWSCON<<4)+(B2_BWSCON<<8)+(B3_BWSCON<<12)+(B4_BWSCON<<16)+(B5_BWSCON<<20)+(B6_BWSCON<<24)+(B7_BWSCON<<28))
    .word ((B0_Tacs<<13)+(B0_Tcos<<11)+(B0_Tacc<<8)+(B0_Tcoh<<6)+(B0_Tah<<4)+(B0_Tacp<<2)+(B0_PMC))
    .word ((B1_Tacs<<13)+(B1_Tcos<<11)+(B1_Tacc<<8)+(B1_Tcoh<<6)+(B1_Tah<<4)+(B1_Tacp<<2)+(B1_PMC))
    .word ((B2_Tacs<<13)+(B2_Tcos<<11)+(B2_Tacc<<8)+(B2_Tcoh<<6)+(B2_Tah<<4)+(B2_Tacp<<2)+(B2_PMC))
    .word ((B3_Tacs<<13)+(B3_Tcos<<11)+(B3_Tacc<<8)+(B3_Tcoh<<6)+(B3_Tah<<4)+(B3_Tacp<<2)+(B3_PMC))
    .word ((B4_Tacs<<13)+(B4_Tcos<<11)+(B4_Tacc<<8)+(B4_Tcoh<<6)+(B4_Tah<<4)+(B4_Tacp<<2)+(B4_PMC))
    .word ((B5_Tacs<<13)+(B5_Tcos<<11)+(B5_Tacc<<8)+(B5_Tcoh<<6)+(B5_Tah<<4)+(B5_Tacp<<2)+(B5_PMC))
    .word ((B6_MT<<15)+(B6_Trcd<<2)+(B6_SCAN))
    .word ((B7_MT<<15)+(B7_Trcd<<2)+(B7_SCAN))
    .word ((REFEN<<23)+(TREFMD<<22)+(Trp<<20)+(Trc<<18)+(Tchr<<16)+REFCNT)
    .word 0x32
    .word 0x30
    .word 0x30

回到文件arch/arm/cpu/arm920t/start.S中,bl  cpu_init_crit的下一条指令是

bl  _main

上面这条指令跳转到了arch/arm/lib/crt0.S 文件中。明天继续

参考博文:http://blog.csdn.net/skyflying2012/article/details/25804209











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