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
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