最近在看AM3358的nand flash，我发现在读nand读时候，设备进行ecc校验时，计算出的ecc全为0
sdk版本是ti-sdk-am335x-evm-08.00.00.00-Linux-x86-Install.bin
uboot版本是u-boot-2014.07-g7e537bf
我在omap_gpmc.c文件中的omap_correct_data_bch函数中，加了一些打印信息
356 /*
357 * omap_correct_data_bch - Compares the ecc read from nand spare area
358 * with ECC registers values and corrects one bit error if it has occured
359 *
360 * @mtd: MTD device structure
361 * @dat: page data
362 * @read_ecc: ecc read from nand flash (ignored)
363 * @calc_ecc: ecc read from ECC registers
364 *
365 * @return 0 if data is OK or corrected, else returns -1
366 */
367 static int omap_correct_data_bch(struct mtd_info *mtd, uint8_t *dat,
368 uint8_t *read_ecc, uint8_t *calc_ecc)
369 {
370 struct nand_chip *chip = mtd->priv;
371 struct omap_nand_info *info = chip->priv;
372 struct nand_ecc_ctrl *ecc = &chip->ecc;
373 uint32_t error_count = 0, error_max;
374 uint32_t error_loc[ELM_MAX_ERROR_COUNT];
375 enum bch_level bch_type;
376 uint32_t i, ecc_flag = 0;
377 uint8_t count, err = 0;
378 uint32_t byte_pos, bit_pos;
379
380 printf("\nread ecc: \n");
381 for (i = 0; i < 13; i++)
382 printf("%02x ", read_ecc[i]);
383
384 printf("\ncalc ecc :\n");
385 for (i = 0; i < 13; i++)
386 printf("%02x ", calc_ecc[i]);
387 printf("\n");
388
然后江编译好的MLO和uboot放在SD卡中，从SD卡启动后，进入uboot的命令行，使用nand read命令去读flash中的数据，发现calc ecc全为0，而且最终没有打印ecc有问题，显示正常读完2048字节的数据
U-Boot# nand read 0x80009000 0x80000 0x800
NAND read: device 0 offset 0x80000, size 0x800
read ecc:
a8 e5 53 f6 b7 4d b8 3b e5 19 07 ba 6e
calc ecc :
00 00 00 00 00 00 00 00 00 00 00 00 00
read ecc:
26 82 b7 42 ea 85 f7 a9 1e 06 9e ca 44
calc ecc :
00 00 00 00 00 00 00 00 00 00 00 00 00
read ecc:
c8 35 ef 86 2f a5 cb 88 b2 0e 57 af 5d
calc ecc :
00 00 00 00 00 00 00 00 00 00 00 00 00
read ecc:
77 94 c7 c7 b4 44 42 90 ef d6 7d 98 4a
calc ecc :
00 00 00 00 00 00 00 00 00 00 00 00 00
2048 bytes read: OK
U-Boot#
我看代码中，每次去读nand读时候，应该是都有调用calculate回调函数去计算ecc的，但是为什么计算出来全为0，
还有就是omap_correct_data_bch代码中elm模式检查错误是个什么模式，是不是就不需要读取的时候计算的calc_ecc了
