（四）u-boot启动流程分析（C语言部分board_r.c）

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;
......
}

同样，board_init_r的实现也很简单，主要是执行init_sequence_r里面定义的初始化

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,
};

还是一样，我们来选择一些属性的函数解释：

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_infoInitialize 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_rearly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_ethaddrEthernet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;
}

主要完成了如下功能：

（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;
}

调用了main_loop( )函数：

/* 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();
}

main_loop流程如下：

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 */
}

运行preboot对应的流程，具体内容，可参考上一节，对preboot的流程有详细的说明。

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();
}

运行secure bootcmd

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 */
}

执行bootcmd之前，有abortboot函数，如果有Ctrl+C，则可断开串口输入。

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。