（四）u-boot启动流程分析（C语言部分board_r.c）
慕宏儒
C语言部分主要集中在两个函数board_init_f和board_init_r，主要是board初始化的前部分（front）及后部分（rear），上一节我们分析了board_init_f函数的实现，这一节我们来看看board_r.c：
common/board_r.c
void board_init_r(gd_t *new_gd, ulong dest_addr)
{
......
for (i = 0; i < ARRAY_SIZE(init_sequence_r); i++)
init_sequence_r[i] += gd->reloc_off;
......
}
init_fnc_t init_sequence_r[] = {
initr_trace,
initr_reloc,
/* TODO: could x86/PPC have this also perhaps? */
#ifdef CONFIG_ARM
initr_caches,
#endif
initr_reloc_global_data,
#if defined(CONFIG_SYS_INIT_RAM_LOCK) && defined(CONFIG_E500)
initr_unlock_ram_in_cache,
#endif
initr_barrier,
initr_malloc,
console_init_m,
#ifdef CONFIG_SYS_NONCACHED_MEMORY
initr_noncached,
#endif
bootstage_relocate,
#ifdef CONFIG_DM
initr_dm,
#endif
#ifdef CONFIG_ARM
board_init, /* Setup chipselects */
#endif
/*
* TODO: printing of the clock inforamtion of the board is now
* implemented as part of bdinfo command. Currently only support for
* davinci SOC's is added. Remove this check once all the board
* implement this.
*/
#ifdef CONFIG_CLOCKS
set_cpu_clk_info, /* Setup clock information */
#endif
stdio_init_tables,
initr_serial,
initr_announce,
INIT_FUNC_WATCHDOG_RESET
#ifdef CONFIG_PPC
initr_trap,
#endif
#ifdef CONFIG_ADDR_MAP
initr_addr_map,
#endif
#if defined(CONFIG_BOARD_EARLY_INIT_R)
board_early_init_r,
#endif
INIT_FUNC_WATCHDOG_RESET
#ifdef CONFIG_LOGBUFFER
initr_logbuffer,
#endif
#ifdef CONFIG_POST
initr_post_backlog,
#endif
INIT_FUNC_WATCHDOG_RESET
#ifdef CONFIG_SYS_DELAYED_ICACHE
initr_icache_enable,
#endif
#if defined(CONFIG_PCI) && defined(CONFIG_SYS_EARLY_PCI_INIT)
/*
* Do early PCI configuration _before_ the flash gets initialised,
* because PCU ressources are crucial for flash access on some boards.
*/
initr_pci,
#endif
#ifdef CONFIG_WINBOND_83C553
initr_w83c553f,
#endif
#ifdef CONFIG_ARCH_EARLY_INIT_R
arch_early_init_r,
#endif
power_init_board,
#ifndef CONFIG_SYS_NO_FLASH
initr_flash,
#endif
INIT_FUNC_WATCHDOG_RESET
#if defined(CONFIG_PPC)
/* initialize higher level parts of CPU like time base and timers */
cpu_init_r,
#endif
#ifdef CONFIG_PPC
initr_spi,
#endif
#if defined(CONFIG_X86) && defined(CONFIG_SPI)
init_func_spi,
#endif
#ifdef CONFIG_CMD_NAND
initr_nand,
#endif
#ifdef CONFIG_CMD_ONENAND
initr_onenand,
#endif
#ifdef CONFIG_GENERIC_MMC
initr_mmc,
#endif
#ifdef CONFIG_HAS_DATAFLASH
initr_dataflash,
#endif
initr_env,
INIT_FUNC_WATCHDOG_RESET
initr_secondary_cpu,
#ifdef CONFIG_SC3
initr_sc3_read_eeprom,
#endif
#if defined(CONFIG_ID_EEPROM) || defined(CONFIG_SYS_I2C_MAC_OFFSET)
mac_read_from_eeprom,
#endif
INIT_FUNC_WATCHDOG_RESET
#if defined(CONFIG_PCI) && !defined(CONFIG_SYS_EARLY_PCI_INIT)
/*
* Do pci configuration
*/
initr_pci,
#endif
stdio_add_devices,
initr_jumptable,
#ifdef CONFIG_API
initr_api,
#endif
console_init_r, /* fully init console as a device */
#ifdef CONFIG_DISPLAY_BOARDINFO_LATE
show_model_r,
#endif
#ifdef CONFIG_ARCH_MISC_INIT
arch_misc_init, /* miscellaneous arch-dependent init */
#endif
#ifdef CONFIG_MISC_INIT_R
misc_init_r, /* miscellaneous platform-dependent init */
#endif
INIT_FUNC_WATCHDOG_RESET
#ifdef CONFIG_CMD_KGDB
initr_kgdb,
#endif
interrupt_init,
#if defined(CONFIG_ARM)
initr_enable_interrupts,
#endif
#ifdef CONFIG_X86
timer_init, /* initialize timer */
#endif
#if defined(CONFIG_STATUS_LED) && defined(STATUS_LED_BOOT)
initr_status_led,
#endif
/* PPC has a udelay(20) here dating from 2002. Why? */
#ifdef CONFIG_CMD_NET
initr_ethaddr,
#endif
#ifdef CONFIG_BOARD_LATE_INIT
board_late_init,
#endif
#ifdef CONFIG_CMD_SCSI
INIT_FUNC_WATCHDOG_RESET
initr_scsi,
#endif
#ifdef CONFIG_CMD_DOC
INIT_FUNC_WATCHDOG_RESET
initr_doc,
#endif
#ifdef CONFIG_BITBANGMII
initr_bbmii,
#endif
#ifdef CONFIG_CMD_NET
INIT_FUNC_WATCHDOG_RESET
initr_net,
#endif
#ifdef CONFIG_POST
initr_post,
#endif
#if defined(CONFIG_CMD_PCMCIA) && !defined(CONFIG_CMD_IDE)
initr_pcmcia,
#endif
#if defined(CONFIG_CMD_IDE)
initr_ide,
#endif
#ifdef CONFIG_LAST_STAGE_INIT
INIT_FUNC_WATCHDOG_RESET
/*
* Some parts can be only initialized if all others (like
* Interrupts) are up and running (i.e. the PC-style ISA
* keyboard).
*/
last_stage_init,
#endif
#ifdef CONFIG_CMD_BEDBUG
INIT_FUNC_WATCHDOG_RESET
initr_bedbug,
#endif
#if defined(CONFIG_PRAM) || defined(CONFIG_LOGBUFFER)
initr_mem,
#endif
#ifdef CONFIG_PS2KBD
initr_kbd,
#endif
run_main_loop,
};
initr_trace 初始化并使能u-boot的tracing system
initr_reloc 设置relocation完成的标志
initr_caches 使能dcache、icache
initr_malloc malloc有关的初始化
initr_dm relocate之后，重新初始化DM
board_init 板级初始化
set_cpu_clk_info Initialize clock framework
initr_serial 重新初始化串口
initr_announce 宣布已经在RAM中执行
board_early_init_r early板级初始化
arch_early_init_r 由arch代码实现
power_init_board 板级的power init代码
initr_flash
initr_nand
initr_onenand
initr_mmc
initr_dataflash 各种flash设备的初始化
initr_env 环境变量有关的初始化。
initr_secondary_cpu 初始化其它的CPU core。
stdio_add_devices 各种输入输出设备的初始化，如LCD driver等。
interrupt_init 中断有关的初始化。
initr_enable_interrupts 使能系统的中断
initr_status_led 状态指示LED的初始化
initr_ethaddr Ethernet的初始化
board_late_init 由板级代码实现
run_main_loop 执行到main_loop
我们主要关注下board相关的初始化，针对board有如上红色标记部分，针对具体的实现，可针对上述函数的初始化具体理解。下面仅看下board_late_init函数
int board_late_init(void){
//update env before anyone using it
run_command("get_rebootmode; echo reboot_mode=${reboot_mode}; "\
"if test ${reboot_mode} = factory_reset; then "\
"defenv_reserv aml_dt;setenv upgrade_step 2;save; fi;", 0);
run_command("if itest ${upgrade_step} == 1; then "\
"defenv_reserv; setenv upgrade_step 2; saveenv; fi;", 0);
/*add board late init function here*/
int ret;
ret = run_command("store dtb read $dtb_mem_addr", 1);
if (ret) {
printf("%s(): [store dtb read $dtb_mem_addr] fail\n", __func__);
#ifdef CONFIG_DTB_MEM_ADDR
char cmd[64];
printf("load dtb to %x\n", CONFIG_DTB_MEM_ADDR);
sprintf(cmd, "store dtb read %x", CONFIG_DTB_MEM_ADDR);
ret = run_command(cmd, 1);
if (ret) {
printf("%s(): %s fail\n", __func__, cmd);
}
#endif
}
..........................//其他相关初始化，省略
return 0;
}
（1）检查reboot_mode，如果是factory_reset,则把env default，然后设置upgrade_step=2
（2）检查upgrade_step，如果为1，则env default ，然后设置upgrade_step=2
（3）从存储设备读取dtb到地址$dtb_mem_addr
执行到最后，进入了run_main_loop函数，我们来看看此函数的实现：
static int run_main_loop(void)
{
#ifdef CONFIG_SANDBOX
sandbox_main_loop_init();
#endif
/* main_loop() can return to retry autoboot, if so just run it again */
for (;;)
main_loop();
return 0;
}
/* We come here after U-Boot is initialised and ready to process commands */
void main_loop(void)
{
const char *s;
.................//省略
run_preboot_environment_command();
#if defined(CONFIG_UPDATE_TFTP)
update_tftp(0UL);
#endif /* CONFIG_UPDATE_TFTP */
s = bootdelay_process();
if (cli_process_fdt(&s))
cli_secure_boot_cmd(s);
...........................//省略
autoboot_command(s);
cli_loop();
}
1. 运行preboot，run_preboot_environment_command()
static void run_preboot_environment_command(void)
{
#ifdef CONFIG_PREBOOT
char *p;
p = getenv("preboot");
if (p != NULL) {
# ifdef CONFIG_AUTOBOOT_KEYED
int prev = disable_ctrlc(1); /* disable Control C checking */
# endif
run_command_list(p, -1, 0);
# ifdef CONFIG_AUTOBOOT_KEYED
disable_ctrlc(prev); /* restore Control C checking */
# endif
}
#endif /* CONFIG_PREBOOT */
}
2. 获取bootcmd，bootdelay_process()
const char *bootdelay_process(void)
{
char *s;
int bootdelay;
.......................//省略
s = getenv("bootcmd");
process_fdt_options(gd->fdt_blob);
stored_bootdelay = bootdelay;
return s;
}
获取bootcmd值
3.如果有bootsecure设置，则执行secure boot，cli_secure_boot_cmd(s)
void cli_secure_boot_cmd(const char *cmd)
{
cmd_tbl_t *cmdtp;
int rc;
if (!cmd) {
printf("## Error: Secure boot command not specified\n");
goto err;
}
/* Disable Ctrl-C just in case some command is used that checks it. */
disable_ctrlc(1);
/* Find the command directly. */
cmdtp = find_cmd(cmd);
if (!cmdtp) {
printf("## Error: \"%s\" not defined\n", cmd);
goto err;
}
/* Run the command, forcing no flags and faking argc and argv. */
rc = (cmdtp->cmd)(cmdtp, 0, 1, (char **)&cmd);
/* Shouldn't ever return from boot command. */
printf("## Error: \"%s\" returned (code %d)\n", cmd, rc);
err:
hang();
}
4. 没有secureboot，执行bootcmd， autoboot_command(s);
void autoboot_command(const char *s)
{
debug("### main_loop: bootcmd=\"%s\"\n", s ? s : "<UNDEFINED>");
if (stored_bootdelay != -1 && s && !abortboot(stored_bootdelay)) {
#if defined(CONFIG_AUTOBOOT_KEYED) && !defined(CONFIG_AUTOBOOT_KEYED_CTRLC)
int prev = disable_ctrlc(1); /* disable Control C checking */
#endif
run_command_list(s, -1, 0);
#if defined(CONFIG_AUTOBOOT_KEYED) && !defined(CONFIG_AUTOBOOT_KEYED_CTRLC)
disable_ctrlc(prev); /* restore Control C checking */
#endif
}
#ifdef CONFIG_MENUKEY
if (menukey == CONFIG_MENUKEY) {
s = getenv("menucmd");
if (s)
run_command_list(s, -1, 0);
}
#endif /* CONFIG_MENUKEY */
}
5.执行完bootcmd
则启动到kerenl阶段，u-boot执行结束。
以上即为board_r.c的启动过程，主要是一些初始化，及启动检查，然后加载内核启动。
参考：http://www.wowotech.net/u-boot/boot_flow_2.html
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