mtk preloader学习笔记

1.先看preloader生成过程，mediatek/buid/makemtk.mk文件里

preloader:

　　...

$(hide) cd $(PRELOADER_WD) && 
(./build.sh $(PROJECT) $(ACTION) $(DEAL_STDOUT) && 
cd $(MKTOPDIR) && 
$(call chkImgSize,$(ACTION),$(PROJECT),$(SCATTER_FILE),$(PRELOADER_IMAGES),$(DEAL_STDOUT),&&) 
$(SHOWRSLT) $$? $(MODULE_LOG) || 
$(SHOWRSLT) $$? $(MODULE_LOG))

...

执行mediatek/source/preloader/build.sh生成的。

2.在build.sh里有

function build_preloader ()

{

　　　...

         make

　　.....

｝

3.执行mediatek/source/preloader/Makefile文件的make命令。

all: $(ALL)
# ELF Generation
#

$(D_BIN)/$(PL_IMAGE_NAME).elf:
$(LD) --gc-sections -Bstatic -T$(MTK_PATH_PLATFORM)/link_descriptor.ld 
$(wildcard $(D_OBJ)/*) $(SECURITY_LIB) -Map system.map -o $(D_BIN)/$(PL_IMAGE_NAME).elf
@$(OBJCOPY) ${OBJCFLAGS} $(D_BIN)/$(PL_IMAGE_NAME).elf -O binary $(D_BIN)/$(PL_IMAGE_NAME).bin 
cat $(MTK_PATH_CUSTOM)/MTK_Loader_Info.tag >> $(D_BIN)/$(PL_IMAGE_NAME).bin

这一句会最终解释为：

arm-eabi-ld --gc-sections -Bstatic -T/home/chyl411/android/alps/mediatek/platform/mt6573/preloader/link_descriptor.ld 
 /home/chyl411/android/alps/mediatek/source/preloader/out/assembly.o

/home/chyl411/android/alps/mediatek/source/preloader/out/... 

...............

/home/chyl411/android/alps/mediatek/platform/mt6573/preloader/src/SecLib.a -Map system.map -o /home/chyl411/android/alps/mediatek/source/preloader/bin/preloader_(工程名)_gb.elf。

用arm-eabi-ld工具配合ld文件生成最终elf。第一行/home/chyl411/android/alps/mediatek/source/preloader/out/assembly.o是指assembly.s文件。

4.assembly.s源码们于mediatekplatformmt6573preloadersrcinit目录下:

....
entry :
    /* Disable watch dog timer & Init CP15 setting */                 
    BL      primary_sys_init
    B     C_Main
....
.globl JumpCmd 
JumpCmd:
      MOV  pc, r0

最终会转入C_Main执行。源码们于同一目录下。

5.C_Main进行一些初始化之后，将uboot拷入DRAM，并跳转到UBOOT命令模式。

void C_Main (void)
{
    SYS_BOOT_REASON reason;
    g_boot_mode = NORMAL_BOOT;

    // pre-process
    pl_sys_init();   

    // check boot reason
#ifdef ENABLE_POWER_ON_VIBRATOR
    reason=pl_check_boot_reason();
#else
    pl_check_boot_reason();
#endif

    //boot security tactics
    pl_security_init();

    // clear SGX core clock
    pl_operate_clock();  

#ifdef ENABLE_POWER_ON_VIBRATOR
    if(reason == BR_POWER_KEY){
              *(volatile unsigned short *)0x7002F7B0 |= 1 << 0 | 6 << 4;

          gpt4_busy_wait_ms (100);

        *(volatile unsigned short *)0x7002F7B0 &= ~(1 << 0);
    }
#endif

    // check cable in or not and charge type
    meta_detection_via_usb();

#ifndef CFG_UART_HANDSHAKE_DISABLE
    //via UART to detect tool 
    meta_detection_via_uart ();  
#endif

    pl_security_check();

    // post process
    pl_post_process ();

    // do other function
    pl_do_other_function();
    
    // load u-boot image to DRAM       
    pl_load_uboot_image ();

    // jump to DRAM to run u-boot image        
    pl_print_title ("Jump U-Boot");
    JumpCmd ((UBOOT_IMG_ADDR));

    while (1);
}

JumpCmd函数在步骤4代码中，跳转到UBOOT_IMG_ADDR处执行。