x210学习记录（一）
启动过程
第一步：CPU上电后先从内部IROM中读取预先设置的代码（BL0）执行，这段代码做了一些基本的初始化并判断选择的启动模式，然后从相应的外部存储器读取启动代码（BL1）到内部IRAM。
第二步：从IRAM去运行读取来的启动代码（BL1）.这段代码负责初始化NandFlash,将BL2读到IRAM，然后运行。
第三步：从IRAM运行BL2,BL2初始化DRAM，然后将操作系统读取到DRAM当中，启动操作系统。
IROM(BL0)启动步骤
（1）Disable the Watch-Dog Timer.
(2) Initialize the instruction cache.
(3) Initialize the stack region.
(4) Initialize the heap region.
(5) Initialize the Block Device Copy Function.
(6) Initialize the PLL and set system clock.
(7) Copy the BL1 to the internal SRAM region.
(8) Verify the checksum of BL1.If checksum fails,IRAM will try the second boot up.(SD/MMC channel 2)
(9) Check if it is secure-boot mode or not. If the security key value is written is s5pv210,it’s secure-boot mode. If it is secure-boot mode,verify the integrity of BL1.
(10) Jump to the start address of BL1.