我修改的代码已经上传到github上，地址：https://github.com/qiaoyuguo/u-boot-2014.04-mini2440.git
参考文档： s3c2440手册（下载地址） mini2440电路图（下载地址） K9F1G08数据手册（下载地址）
参考文章：《mini2440移植uboot 2011.03(下)》
前两篇博文： 《mini2440移植uboot 2014.04(一)》
（五）添加nand flash支持
主要是基于参考mini2440 自带的uboot源代码进行修改。
用官方uboot启动时，得到的输出信息是128MiB的nand flash。查看芯片电路图可以知道是K9F系列芯片，而128MiB的芯片只能是K9F1G08（128Mx8bits)。
在上一节执行uboot时，关于nand flash的显示信息如下：
NAND: board_nand_init() end of nand_init hwcontrol(): 0xff 0x83 hwcontrol(): 0xffffffff 0x81 dev_ready hwcontrol(): 0x90 0x83 hwcontrol(): 0x00 0x85 hwcontrol(): 0xffffffff 0x81 dev_ready hwcontrol(): 0x90 0x83 hwcontrol(): 0x00 0x85 hwcontrol(): 0xffffffff 0x81 dev_ready hwcontrol(): 0xffffffff 0x80 0 MiB
明显没有检测到nand flash.
整个调用入口是nand_init->nand_init_chip->board_nand_init，而board_nand_init函数位于drivers/mtd/nand/s3c2410_nand.c中 。
首先需要考虑的就是几个变量的值：tacls、twrph0、twrph1。
参考文章《uboot中nand flash控制器参数TACLS、TWRPH0和TWRPH1的确定(基于K9F2G08U0B)》,这三个值是根据时序来计算出来的。
根据K9F1G08手册第17页和第10页以及s3c2440手册587页，可以知道tacls=tCLS>12ns,twrph0=tWP>12ns,twrph1=tCLH>5ns。
而nand flash是根据HCLK时钟来计算，根据1:4:8的分频，HCLK=100MHZ,每个时钟=10ns.
可以将这三个值分别设置成2、2、1即可，但是为了保持和官方版本一致，我仍将其值设置成4、2、0.
根据2440手册第226页，其NFCONT寄存器中每一位的含义与s3c2410中的大部分都不相同，需要进行相应的修改。
我只是将mini2440中的uboot和当前代码合并，修改代码如下：
#ifdef CONFIG_S3C2410 #define S3C2410_NFCONF_EN (1<<15) #define S3C2410_NFCONF_512BYTE (1<<14) #define S3C2410_NFCONF_4STEP (1<<13) #define S3C2410_NFCONF_INITECC (1<<12) #define S3C2410_NFCONF_nFCE (1<<11) #define S3C2410_NFCONF_TACLS(x) ((x)<<8) #define S3C2410_NFCONF_TWRPH0(x) ((x)<<4) #define S3C2410_NFCONF_TWRPH1(x) ((x)<<0) #define S3C2410_ADDR_NALE 4 #define S3C2410_ADDR_NCLE 8 #endif #ifdef CONFIG_S3C2440 #define S3C2410_NFCONT_EN (1<<0) #define S3C2410_NFCONT_INITECC (1<<4) #define S3C2410_NFCONT_nFCE (1<<1) #define S3C2410_NFCONT_MAINECCLOCK (1<<5) #define S3C2410_NFCONF_TACLS(x) ((x)<<12) #define S3C2410_NFCONF_TWRPH0(x) ((x)<<8) #define S3C2410_NFCONF_TWRPH1(x) ((x)<<4) #define S3C2410_ADDR_NALE 0x08 #define S3C2410_ADDR_NCLE 0x0c #endif
#if defined(CONFIG_S3C2410)
if (ctrl & NAND_NCE)
writel(readl(&nand->nfconf) & ~S3C2410_NFCONF_nFCE,
&nand->nfconf);
else
writel(readl(&nand->nfconf) | S3C2410_NFCONF_nFCE,
&nand->nfconf);
}
#endif
#if defined(CONFIG_S3C2440)
if (ctrl & NAND_NCE)
writel(readl(&nand->nfconf) & ~S3C2410_NFCONT_nFCE,
&nand->nfconf);
else
writel(readl(&nand->nfconf) | S3C2410_NFCONT_nFCE,
&nand->nfconf);
}
#endif
#if defined(CONFIG_S3C2410)
writel(readl(&nand->nfconf) | S3C2410_NFCONF_INITECC, &nand->nfconf);
#endif
#if defined(CONFIG_S3C2440)
writel(readl(&nand->nfconf) | S3C2410_NFCONT_INITECC, &nand->nfconf);
#endif
#if defined(CONFIG_S3C2410)
/* initialize hardware */
#if defined(CONFIG_S3C24XX_CUSTOM_NAND_TIMING)
tacls = CONFIG_S3C24XX_TACLS;
twrph0 = CONFIG_S3C24XX_TWRPH0;
twrph1 = CONFIG_S3C24XX_TWRPH1;
#else
tacls = 4;
twrph0 = 8;
twrph1 = 8;
#endif
#endif
#if defined(CONFIG_S3C2440)
tacls = 4;
twrph0 = 2;
twrph1 = 0;
cfg = 0;
cfg |= S3C2410_NFCONF_TACLS(tacls - 1);
cfg |= S3C2410_NFCONF_TWRPH0(twrph0 - 1);
cfg |= S3C2410_NFCONF_TWRPH1(twrph1 - 1);
writel(cfg, &nand_reg->nfconf);
cfg = (1<<4)|(1<<0);
writel(cfg, &nand_reg->nfcont);
#else
cfg = S3C2410_NFCONF_EN;
cfg |= S3C2410_NFCONF_TACLS(tacls - 1);
cfg |= S3C2410_NFCONF_TWRPH0(twrph0 - 1);
cfg |= S3C2410_NFCONF_TWRPH1(twrph1 - 1);
writel(cfg, &nand_reg->nfconf);
writel(cfg, &nand_reg->nfcont);
#endif
重新编译加载到mini2440,得到输出信息如下：
NAND: board_nand_init() end of nand_init hwcontrol(): 0xff 0x83 hwcontrol(): 0xffffffff 0x81 dev_ready hwcontrol(): 0x90 0x83 hwcontrol(): 0x00 0x85 hwcontrol(): 0xffffffff 0x81 dev_ready hwcontrol(): 0x90 0x83 hwcontrol(): 0x00 0x85 hwcontrol(): 0xffffffff 0x81 dev_ready hwcontrol(): 0xffffffff 0x80 128 MiB
执行一些命令，得到的输出信息：
SMDK2410 # nand info Device 0: nand0, sector size 128 KiB Page size 2048 b OOB size 64 b Erase size 131072 b Initial value for argc=3 Final value for argc=3 Initial value for argc=3 Final value for argc=3 Initial value for argc=3 Final value for argc=3
貌似nand flash基本支持已经完成了，后面使用有问题了再修改代码。
执行了几个nand命令，重新加载uboot到mini2440,却出现下面的错误：
U-Boot 2014.04-g9541fe9-dirty (Jun 05 2014 - 15:45:56) U-Boot code: 33E80000 -> 33EF9ED0 BSS: -> 33F488D0 CPUID: 32440001 FCLK: 405 MHz HCLK: 101.250 MHz PCLK: 50.625 MHz monitor len: 000C88D0 ramsize: 04000000 TLB table from 33ff0000 to 33ff4000 Top of RAM usable for U-Boot at: 33ff0000 Reserving 802k for U-Boot at: 33f27000 Reserving 4160k for malloc() at: 33b17000 Reserving 32 Bytes for Board Info at: 33b16fe0 Reserving 160 Bytes for Global Data at: 33b16f40 New Stack Pointer is: 33b16f30 RAM Configuration: Bank #0: 30000000 64 MiB addr=33f27000,_start=33e80000 relocation Offset is: 000a7000 WARNING: Caches not enabled monitor flash len: 000846C0 dram_bank_mmu_setup: bank: 0 Now running in RAM - U-Boot at: 33f27000 Flash: fwc addr 00000000 cmd f0 00f0 16bit x 16 bit fwc addr 0000aaaa cmd aa 00aa 16bit x 16 bit fwc addr 00005554 cmd 55 0055 16bit x 16 bit fwc addr 0000aaaa cmd 90 0090 16bit x 16 bit fwc addr 00000000 cmd f0 00f0 16bit x 16 bit JEDEC PROBE: ID f0 ffff 0 fwc addr 00000000 cmd ff 00ff 16bit x 16 bit fwc addr 00000000 cmd 90 0090 16bit x 16 bit fwc addr 00000000 cmd ff 00ff 16bit x 16 bit JEDEC PROBE: ID 90 ffff 0 *** failed *** ### ERROR ### Please RESET the board ###
居然又无法检测到nor flash了。我折腾了好一会儿，将nand flash全部擦除，然后将官方的uboot重新加载进来，
之后再加载自己的uboot，能正常进入到uboot命令行了。