STEPLDR启动程序分析

     STEPLDR是用来加载EBOOT的，即引导EBOOT的启动。STEPLDR主要包括两部分：StartUp.s 与 main.c，StartUp.s 主要是初始化CPU，引导EBOOT的功能主要在main.C中完成，该部分结构和代码都比较简单，代码如下：

void main(void) { register nBlock; register nPage; register nBadBlocks; volatile unsigned char *pBuf; // Set up copy section (initialized globals). // // NOTE: after this call, globals become valid. //空函数什么都不做 SetupCopySection(pTOC); // Enable the ICache. //System_EnableICache(); // I-Cache was already enabled in startup.s // Set up all GPIO ports for LED. Port_Init(); Led_Display(0xf); // UART Initialize //Uart_Init(); //Uart_SendString("/r/nWinCE 6.0 Steploader for SMDKC100/r/n"); // Initialize the NAND flash interface. //Uart_SendString("NAND Initialize/n/r"); NAND_Init(); // Copy image from NAND flash to RAM. pBuf = (unsigned char *)LOAD_ADDRESS_PHYSICAL; nBadBlocks = 0; Led_Display(0x8); for (nPage = LOAD_IMAGE_PAGE_OFFSET; nPage < (LOAD_IMAGE_PAGE_OFFSET + LOAD_IMAGE_PAGE_COUNT) ; nPage++) { //Led_Display(0x1); nBlock = ((nPage / NAND_PAGES_PER_BLOCK) + nBadBlocks); if (!NAND_ReadPage(nBlock, (nPage % NAND_PAGES_PER_BLOCK), pBuf)) { if ((nPage % NAND_PAGES_PER_BLOCK) != 0) { Led_Display(0x9); // real ECC Error. //Uart_SendString("ECC Error./r/n"); while(1) { // Spin forever... } } // ECC error on a block boundary is (likely) a bad block - retry the page 0 read on the next block. nBadBlocks++; nPage--; continue; } pBuf += NAND_BYTES_PER_PAGE; } Led_Display(0x0); //Uart_SendString("Launch Eboot.../n/r"); ((PFN_IMAGE_LAUNCH)(LOAD_ADDRESS_PHYSICAL))(); }

我们从头来看起，首先是一个SetupCopySection(pTOC),该函数是一个空函数，如下：

static BOOLEAN SetupCopySection(ROMHDR *const pTOC)
{
    // This code doesn't make use of global variables so there are no copy sections.
    // To reduce code size, this is a stub function...
    return(TRUE);
}

注释说这是一个stub function,不明白什么意思。接着是GPIO端口和LED指示灯的初始化，然后就是NAND FLASH的初始化。注意，这部分中没有初始化串口，主要是为了加快启动速度。若要在这部分输出信息就有进行串口初始化。

pBuf = (unsigned char *)LOAD_ADDRESS_PHYSICAL; 其中的“LOAD_ADDRESS_PHYSICAL”就是要将EBOOT下载到的地址，位于DRAM，值为0X20030000。初始化完成以后就开始加载EBOOT了：

    for (nPage = LOAD_IMAGE_PAGE_OFFSET; nPage < (LOAD_IMAGE_PAGE_OFFSET + LOAD_IMAGE_PAGE_COUNT) ; nPage++)
    {
        //Led_Display(0x1);
        nBlock = ((nPage / NAND_PAGES_PER_BLOCK) + nBadBlocks);

        if (!NAND_ReadPage(nBlock, (nPage % NAND_PAGES_PER_BLOCK), pBuf))
        {
            if ((nPage % NAND_PAGES_PER_BLOCK) != 0)
            {
                Led_Display(0x9);    // real ECC Error.
                //Uart_SendString("ECC Error./r/n");

                while(1)
                {
                    // Spin forever...
                }
            }

            // ECC error on a block boundary is (likely) a bad block - retry the page 0 read on the next block.
            nBadBlocks++;
            nPage--;

            continue;
        }

        pBuf += NAND_BYTES_PER_PAGE;
    }

其中EBOOT的大小事先定义好的。加载好EBOOT以后就要运行它了：((PFN_IMAGE_LAUNCH)(LOAD_ADDRESS_PHYSICAL))();其中的PFN_IMAGE_LAUNCH是一个定义的空函数指针：typedef void (*PFN_IMAGE_LAUNCH)();这种方式比较巧妙。这样EBOOT就运行起来了。