Cubietruck---4. boot0源码流程简略分析

大体上看了一下boot0的代码,没有找到交叉编译的工具,所以也没有编译实验一下(即以下分析可能有错).
boot0的代码在./lichee/boot/boot0目录下:
1. 开始的代码
这部分代码准备了c语言的环境,并跳到c函数Boot0_C_part中
Boot0.slichee/boot/boot0/Boot0.s

INCLUDE boot0_i.inc
        IMPORT   Boot0_C_part
        IMPORT   set_pll
        PRESERVE8
        AREA  init, CODE, READONLY
        CODE32
        ENTRY
initialize
    //设置当前运行SVC模式
    mrs r0, cpsr
    bic r0, r0, #ARMV7_MODE_MASK
    orr r0, r0, #ARMV7_SVC_MODE
    orr r0, r0, #( ARMV7_IRQ_MASK | ARMV7_FIQ_MASK ) ;// After reset, ARM automaticly disables IRQ and FIQ, and runs in SVC mode.
    bic r0, r0, #ARMV7_CC_E_BIT                      ;// set little-endian
    msr cpsr_c, r0


    //关mmu, data cache, icache, flow prediction,align
    mrc p15, 0, r0, c1, c0
    bic r0, r0, #( ARMV7_C1_M_BIT | ARMV7_C1_C_BIT )    ;// disable MMU, data cache
    bic r0, r0, #( ARMV7_C1_I_BIT | ARMV7_C1_Z_BIT )    ;// disable instruction cache, disable flow prediction
    bic r0, r0, #( ARMV7_C1_A_BIT)                      ;// disable align
    mcr p15, 0, r0, c1, c0

    //为运行C语言设置栈
    ldr sp, =BOOT0_STACK_BOTTOM
    //调用C函数set_pll,设置cpu频率
    bl set_pll
    //调用C函数Boot0_C_part
    bl Boot0_C_part

     b . ;// infinite loop
END

2. 进入
然后调用文件Boot0_C_part.c中的Boot0_C_part

void Boot0_C_part( void )
{
    __u32 status;
    __s32 dram_size;
    //将boot0的代码由 Load$$Boot0_RW_ZI$$Base复制到Image$$Boot0_RW_ZI$$Base
    move_RW( );
    //清bss
    clear_ZI( );
    //设置了各个clock,具体哪个没看
    timer_init();
    //初始化串口,以后就可以打印了
    UART_open( BT0_head.prvt_head.uart_port, (void *)BT0_head.prvt_head.uart_ctrl, 24*1000*1000 );
    //打印
    print_version();

    //以下就是一些初始化
    ...
    //在文件./lichee/boot/config/storage_media_cfg/nand/storage_media_cfg.h中配置了启动设备
    #if SYS_STORAGE_MEDIA_TYPE == SYS_STORAGE_MEDIA_NAND_FLASH
       //初始化nand flash,读取nand上的第2块(烧录时boot1写在了这个地方),第2块开头有一些数据记录了boot1的大小,
       //按这个大小数取整个的boot1到内存的BOOT1_BASE(0x42400000)处
        status = load_Boot1_from_nand( );
    #elif SYS_STORAGE_MEDIA_TYPE == SYS_STORAGE_MEDIA_SPI_NOR_FLASH
        status = load_boot1_from_spinor( );
    #elif SYS_STORAGE_MEDIA_TYPE == SYS_STORAGE_MEDIA_SD_CARD
        status = load_boot1_from_sdmmc( (char *)BT0_head.prvt_head.storage_data ); // ????boot1
    #else
        #error The storage media of Boot1 has not been defined.
    #endif

    mmu_disable( ); // disable instruction cache

    if( status == OK )
    {
        set_dram_para((void *)&BT0_head.prvt_head.dram_para, dram_size);
        set_nand_good_block_ratio_para((void *)&BT0_head.prvt_head.storage_data);
        jump_to( BOOT1_BASE );                 //跳到BOOT1_BASE处,开始执行boot1的东东
    }
}

注: boot0的交叉编译工具链是在lichee/boot/config/ARMCC_CROSSTOOL.CFG中有定义的,需要ARMRVDS.不知上哪儿找这个东东.