AM335x(TQ335x)学习笔记——u-boot-2014.10移植

根据最近移植u-boot-2014.10至TQ335x，基于这样的假设am335x evm移植。不是很多地方需要改变。

因为TI的am335x evm开发了使用eeprom船上保存配置信息。它使用不同类型的电路板来区分，和TQ335x如果没有这个eeprom。因此。须要改动eeprom相关的部分，使u-boot适应TQ335x开发板。

使用source insight查看代码，非常easy发现，全部获取板载配置的部分都是通过读取eeprom获得的，因此，首选改动read_eeprom（board/ti/am335x/board.c）函数。详细的改动例如以下：

static int read_eeprom(struct am335x_baseboard_id *header)
{
#if 1
	strcpy(header->name, "TQ335x");
#else
	/* Check if baseboard eeprom is available */
	if (i2c_probe(CONFIG_SYS_I2C_EEPROM_ADDR)) {
		puts("Could not probe the EEPROM; something fundamentally "
			"wrong on the I2C bus.\n");
		return -ENODEV;
	}

	/* read the eeprom using i2c */
	if (i2c_read(CONFIG_SYS_I2C_EEPROM_ADDR, 0, 2, (uchar *)header,
		     sizeof(struct am335x_baseboard_id))) {
		puts("Could not read the EEPROM; something fundamentally"
			" wrong on the I2C bus.\n");
		return -EIO;
	}

	if (header->magic != 0xEE3355AA) {
		/*
		 * read the eeprom using i2c again,
		 * but use only a 1 byte address
		 */
		if (i2c_read(CONFIG_SYS_I2C_EEPROM_ADDR, 0, 1, (uchar *)header,
			     sizeof(struct am335x_baseboard_id))) {
			puts("Could not read the EEPROM; something "
				"fundamentally wrong on the I2C bus.\n");
			return -EIO;
		}

		if (header->magic != 0xEE3355AA) {
			printf("Incorrect magic number (0x%x) in EEPROM\n",
					header->magic);
			return -EINVAL;
		}
	}
#endif

	return 0;
}

通过上述改动，u-boot不去读取eeprom，而是直接将header的name赋值为"TQ335x"，后面能够依据这一配置区分是否为TQ335x开发板。

然后是改动get_dpll_ddr_params（board/ti/am335x/board.c）函数，详细的改动内容例如以下：

const struct dpll_params *get_dpll_ddr_params(void)
{
	struct am335x_baseboard_id header;

	enable_i2c0_pin_mux();
	i2c_init(CONFIG_SYS_OMAP24_I2C_SPEED, CONFIG_SYS_OMAP24_I2C_SLAVE);
	if (read_eeprom(&header) < 0)
		puts("Could not get board ID.\n");

	if (board_is_tq335x(&header) || board_is_evm_sk(&header))
		return &dpll_ddr_evm_sk;
	else if (board_is_bone_lt(&header))
		return &dpll_ddr_bone_black;
	else if (board_is_evm_15_or_later(&header))
		return &dpll_ddr_evm_sk;
	else
		return &dpll_ddr;
}

然后是改动sdram_init（board/ti/am335x/board.c）函数，详细的改动内容例如以下：

void sdram_init(void)
{
	__maybe_unused struct am335x_baseboard_id header;

	if (read_eeprom(&header) < 0)
		puts("Could not get board ID.\n");

	if (board_is_evm_sk(&header)) {
		/*
		 * EVM SK 1.2A and later use gpio0_7 to enable DDR3.
		 * This is safe enough to do on older revs.
		 */
		gpio_request(GPIO_DDR_VTT_EN, "ddr_vtt_en");
		gpio_direction_output(GPIO_DDR_VTT_EN, 1);
	}

	if (board_is_evm_sk(&header) || board_is_tq335x(&header))
		config_ddr(303, &ioregs_evmsk, &ddr3_data,
			   &ddr3_cmd_ctrl_data, &ddr3_emif_reg_data, 0);
	else if (board_is_bone_lt(&header))
		config_ddr(400, &ioregs_bonelt,
			   &ddr3_beagleblack_data,
			   &ddr3_beagleblack_cmd_ctrl_data,
			   &ddr3_beagleblack_emif_reg_data, 0);
	else if (board_is_evm_15_or_later(&header))
		config_ddr(303, &ioregs_evm15, &ddr3_evm_data,
			   &ddr3_evm_cmd_ctrl_data, &ddr3_evm_emif_reg_data, 0);
	else
		config_ddr(266, &ioregs, &ddr2_data,
			   &ddr2_cmd_ctrl_data, &ddr2_emif_reg_data, 0);
}

然后加入board_is_tq335x函数的详细实现，參考其他类似函数实现就可以，因为我们的read_eeprom仅读到了name，其内容是"TQ335x"，故可例如以下实现。在board/ti/am335x/board.h中加入例如以下内容：

static inline int board_is_tq335x(struct am335x_baseboard_id *header)
{
	return !strncmp(header->name, "TQ335x", HDR_NAME_LEN);
}

最后是改动enable_board_pin_mux（board/ti/am335x/mux.c）函数，详细的改动内容例如以下：

void enable_board_pin_mux(struct am335x_baseboard_id *header)
{
	/* Do board-specific muxes. */
	if (board_is_bone(header) || board_is_tq335x(header)) {
		/* Beaglebone pinmux */
		configure_module_pin_mux(i2c1_pin_mux);
		configure_module_pin_mux(mii1_pin_mux);
		configure_module_pin_mux(mmc0_pin_mux);
#if defined(CONFIG_NAND)
		configure_module_pin_mux(nand_pin_mux);
#elif defined(CONFIG_NOR)
		configure_module_pin_mux(bone_norcape_pin_mux);
#else
		configure_module_pin_mux(mmc1_pin_mux);
#endif
	} else if (board_is_gp_evm(header)) {
		/* General Purpose EVM */
		unsigned short profile = detect_daughter_board_profile();
		configure_module_pin_mux(rgmii1_pin_mux);
		configure_module_pin_mux(mmc0_pin_mux);
		/* In profile #2 i2c1 and spi0 conflict. */
		if (profile & ~PROFILE_2)
			configure_module_pin_mux(i2c1_pin_mux);
		/* Profiles 2 & 3 don't have NAND */
#ifdef CONFIG_NAND
		if (profile & ~(PROFILE_2 | PROFILE_3))
			configure_module_pin_mux(nand_pin_mux);
#endif
		else if (profile == PROFILE_2) {
			configure_module_pin_mux(mmc1_pin_mux);
			configure_module_pin_mux(spi0_pin_mux);
		}
	} else if (board_is_idk(header)) {
		/* Industrial Motor Control (IDK) */
		configure_module_pin_mux(mii1_pin_mux);
		configure_module_pin_mux(mmc0_no_cd_pin_mux);
	} else if (board_is_evm_sk(header)) {
		/* Starter Kit EVM */
		configure_module_pin_mux(i2c1_pin_mux);
		configure_module_pin_mux(gpio0_7_pin_mux);
		configure_module_pin_mux(rgmii1_pin_mux);
		configure_module_pin_mux(mmc0_pin_mux_sk_evm);
	} else if (board_is_bone_lt(header)) {
		/* Beaglebone LT pinmux */
		configure_module_pin_mux(i2c1_pin_mux);
		configure_module_pin_mux(mii1_pin_mux);
		configure_module_pin_mux(mmc0_pin_mux);
#if defined(CONFIG_NAND)
		configure_module_pin_mux(nand_pin_mux);
#elif defined(CONFIG_NOR)
		configure_module_pin_mux(bone_norcape_pin_mux);
#else
		configure_module_pin_mux(mmc1_pin_mux);
#endif
	} else {
		puts("Unknown board, cannot configure pinmux.");
		hang();
	}
}

另外，这个版本号的u-boot有个bug。须要改动fat_register_device（fs/fat/fat.c）函数：

int fat_register_device(block_dev_desc_t *dev_desc, int part_no)
{
	disk_partition_t info;

	/* First close any currently found FAT filesystem */
	cur_dev = NULL;

	/* Read the partition table, if present */
	if (get_partition_info(dev_desc, part_no, &info)) {
		/*if (part_no != 0) {
			printf("** Partition %d not valid on device %d **\n",
					part_no, dev_desc->dev);
			return -1;
		}*/

		info.start = 0;
		info.size = dev_desc->lba;
		info.blksz = dev_desc->blksz;
		info.name[0] = 0;
		info.type[0] = 0;
		info.bootable = 0;
#ifdef CONFIG_PARTITION_UUIDS
		info.uuid[0] = 0;
#endif
	}

	return fat_set_blk_dev(dev_desc, &info);
}

至此，u-boot就已经能够启动了，可是有多余的步骤和log。只是能够去掉。改动file_fat_read_at（fs/fat/fat.c）函数：

long file_fat_read_at(const char *filename, unsigned long pos, void *buffer,
		      unsigned long maxsize)
{
	debug("reading %s\n", filename);
	return do_fat_read_at(filename, pos, buffer, maxsize, LS_NO, 0);
}

最后，TQ335x是MLO启动u-boot。然后u-boot去启动内核。故能够去掉配置项CONFIG_SPL_OS_BOOT，详细的改动文件include/configs/ti_armv7_common.h：

#if defined(CONFIG_SPL_OS_BOOT_ENABLE)
#define CONFIG_SPL_OS_BOOT
#endif

至此，u-boot的移植工作就完毕了，编译方法例如以下：

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- am335x_evm_defconfig
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- -j8

当中，arm-linux-gnueabi-须要依据自己的交叉编译工具链前缀进行改动。完毕u-boot的移植工作后我们来研究怎样启动内核。

源代码下载地址：

u-boot-2014.10 for TQ335x/TQ3358(SD卡启动)

本文作者：girlkoo

本文链接：http://blog.csdn.net/girlkoo/article/details/41183217