2440从NANDFlash启动之bootloader运行以前

一直对2440上电以后怎么从nandflash中启动不是很清楚,闲来无事看了下s3c2440的用户手册,看到下面这样一段话:
S3C2440A boot code can be executed on an external NAND flash memory. In order to support NAND flash bootloader, the S3C2440A is equipped with an internal SRAM buffer called "Steppingstone". When booting, the first 4KBytes of the NAND flash memory will be loaded into Steppingstone and the boot code loaded into Steppingstone will be executed.
Generally, the boot code will copy NAND flash content to SDRAM. Using hardware ECC generating, the NAND flash data validity will be checked. Upon the completion of the copy, the main program will be executed on the SDRAM.
虽然大家都看得懂上面的eng,但是为了自己以后看得方便一些,在此稍微解释一下:
2440的启动代码可以从外部的nandflash上执行。为了能支持nboot,2440需要带有一个叫做steppingstone的内部sram缓冲区。在启动加载的时候,nandflash的前4k的内容(nboot部分)要被先load到steppingstone中去(此时steppingstone被映射为物理地址的0x0,复位后执行的第一条指令就是从这里取的),并且接着就是在steppingstone中去执行该启动代码。这部分代码(nboot)的作用是会将nandflash中的bootloader step2部分拷贝到sdram中去,并跳到sdram中去执行以加载内核(nk)。
nboot从nandflash被load到steppingstone中的过程为:在上点的时候,nandflash控制器通过几个引脚的状态(NCON-Adv flash;GPG13-Page size;GPG14-Address cycle;GPG15-Bus width)来得到nandflash的相关信息,之后nandflash控制器就会自动load nandflash中前4k的启动代码到steppingstone中去,并在其中执行了。

本文出自 “bluefish” 博客,请务必保留此出处http://bluefish.blog.51cto.com/214870/67093

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