AM335x(TQ335x)学习笔记——u-boot-2014.10移植
最近移植了下u-boot-2014.10到TQ335x，如果基于am335x evm进行移植，需要修改的地方并不多。由于TI的am335x evm开发使用了一个eeprom保存了板载配置信息，用来区分不同板子的型号的，而TQ335x没有这个eeprom，因此，需要修改eeprom相关的部分，使u-boot适应TQ335x开发板。
使用source insight查看代码，很容易发现，所有获取板载配置的部分都是通过读取eeprom获得的，因此，首选修改read_eeprom(board/ti/am335x/board.c)函数，具体的修改如下：
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;
}
通过上述修改，u-boot不去读取eeprom，而是直接将header的name赋值为"TQ335x"，后面可以根据这一配置区分是否为TQ335x开发板。然后是修改get_dpll_ddr_params(board/ti/am335x/board.c)函数，具体的修改内容如下：
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;
}
然后是修改sdram_init(board/ti/am335x/board.c)函数，具体的修改内容如下：
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);
}
然后添加board_is_tq335x函数的具体实现，参考其它类似函数实现即可，由于我们的read_eeprom仅读到了name，其内容是"TQ335x"，故可如下实现，在board/ti/am335x/board.h中添加如下内容：
static inline int board_is_tq335x(struct am335x_baseboard_id *header)
{
return !strncmp(header->name, "TQ335x", HDR_NAME_LEN);
}
最后是修改enable_board_pin_mux(board/ti/am335x/mux.c)函数，具体的修改内容如下：
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，这个版本的u-boot有个bug，需要修改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;
info.type = 0;
info.bootable = 0;
#ifdef CONFIG_PARTITION_UUIDS
info.uuid = 0;
#endif
}
return fat_set_blk_dev(dev_desc, &info);
}
至此，u-boot就已经可以启动了，但是有多余的步骤和log，不过可以去掉，修改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，故可以去掉配置项CONFIG_SPL_OS_BOOT，具体的修改文件include/configs/ti_armv7_common.h：
#if defined(CONFIG_SPL_OS_BOOT_ENABLE)
#define CONFIG_SPL_OS_BOOT
#endif
至此，u-boot的移植工作就完成了，编译方法如下：
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- am335x_evm_defconfig
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- -j8
其中，arm-linux-gnueabi-需要根据自己的交叉编译工具链前缀进行修改。完成u-boot的移植工作后我们来研究如何启动内核。
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