uboot入口

arch/arm/lib/crt0.S

#include <config.h>
#include <asm-offsets.h>
#include <linux/linkage.h>

/*
 * This file handles the target-independent stages of the U-Boot
 * start-up where a C runtime environment is needed. Its entry point
 * is _main and is branched into from the target's start.S file.
 *
 * _main execution sequence is:
 *
 * 1. Set up initial environment for calling board_init_f().
 *    This environment only provides a stack and a place to store
 *    the GD ('global data') structure, both located in some readily
 *    available RAM (SRAM, locked cache...). In this context, VARIABLE
 *    global data, initialized or not (BSS), are UNAVAILABLE; only
 *    CONSTANT initialized data are available.
 *
 * 2. Call board_init_f(). This function prepares the hardware for
 *    execution from system RAM (DRAM, DDR...) As system RAM may not
 *    be available yet, , board_init_f() must use the current GD to
 *    store any data which must be passed on to later stages. These
 *    data include the relocation destination, the future stack, and
 *    the future GD location.
 *
 * (the following applies only to non-SPL builds)
 *
 * 3. Set up intermediate environment where the stack and GD are the
 *    ones allocated by board_init_f() in system RAM, but BSS and
 *    initialized non-const data are still not available.
 *
 * 4. Call relocate_code(). This function relocates U-Boot from its
 *    current location into the relocation destination computed by
 *    board_init_f().
 *
 * 5. Set up final environment for calling board_init_r(). This
 *    environment has BSS (initialized to 0), initialized non-const
 *    data (initialized to their intended value), and stack in system
 *    RAM. GD has retained values set by board_init_f(). Some CPUs
 *    have some work left to do at this point regarding memory, so
 *    call c_runtime_cpu_setup.
 *
 * 6. Branch to board_init_r().
 */

/*
 * entry point of crt0 sequence
 */

ENTRY(_main)

/*
 * Set up initial C runtime environment and call board_init_f(0).
 */

#if defined(CONFIG_SPL_BUILD) && defined(CONFIG_SPL_STACK)
	ldr	sp, =(CONFIG_SPL_STACK)
#else
	ldr	sp, =(CONFIG_SYS_INIT_SP_ADDR)
#endif
	bic	sp, sp, #7	/* 8-byte alignment for ABI compliance */
	mov	r2, sp
	sub	sp, sp, #GD_SIZE	/* allocate one GD above SP */
	bic	sp, sp, #7	/* 8-byte alignment for ABI compliance */
	mov	r9, sp		/* GD is above SP */
	mov	r1, sp
	mov	r0, #0
clr_gd:
	cmp	r1, r2			/* while not at end of GD */
	strlo	r0, [r1]		/* clear 32-bit GD word */
	addlo	r1, r1, #4		/* move to next */
	blo	clr_gd
#if defined(CONFIG_SYS_MALLOC_F_LEN)
	sub	sp, sp, #CONFIG_SYS_MALLOC_F_LEN
	str	sp, [r9, #GD_MALLOC_BASE]
#endif
	/* mov r0, #0 not needed due to above code */
	bl	board_init_f

#if ! defined(CONFIG_SPL_BUILD)

/*
 * Set up intermediate environment (new sp and gd) and call
 * relocate_code(addr_moni). Trick here is that we'll return
 * 'here' but relocated.
 */

	ldr	sp, [r9, #GD_START_ADDR_SP]	/* sp = gd->start_addr_sp */
	bic	sp, sp, #7	/* 8-byte alignment for ABI compliance */
	ldr	r9, [r9, #GD_BD]		/* r9 = gd->bd */
	sub	r9, r9, #GD_SIZE		/* new GD is below bd */

	adr	lr, here
	ldr	r0, [r9, #GD_RELOC_OFF]		/* r0 = gd->reloc_off */
	add	lr, lr, r0
	ldr	r0, [r9, #GD_RELOCADDR]		/* r0 = gd->relocaddr */
	b	relocate_code
here:
/*
 * now relocate vectors
 */

	bl	relocate_vectors

/* Set up final (full) environment */

	bl	c_runtime_cpu_setup	/* we still call old routine here */
#endif
#if !defined(CONFIG_SPL_BUILD) || defined(CONFIG_SPL_FRAMEWORK)
# ifdef CONFIG_SPL_BUILD
	/* Use a DRAM stack for the rest of SPL, if requested */
	bl	spl_relocate_stack_gd
	cmp	r0, #0
	movne	sp, r0
# endif
	ldr	r0, =__bss_start	/* this is auto-relocated! */

#ifdef CONFIG_USE_ARCH_MEMSET
	ldr	r3, =__bss_end		/* this is auto-relocated! */
	mov	r1, #0x00000000		/* prepare zero to clear BSS */

	subs	r2, r3, r0		/* r2 = memset len */
	bl	memset
#else
	ldr	r1, =__bss_end		/* this is auto-relocated! */
	mov	r2, #0x00000000		/* prepare zero to clear BSS */

clbss_l:cmp	r0, r1			/* while not at end of BSS */
	strlo	r2, [r0]		/* clear 32-bit BSS word */
	addlo	r0, r0, #4		/* move to next */
	blo	clbss_l
#endif

#if ! defined(CONFIG_SPL_BUILD)
	bl coloured_LED_init
	bl red_led_on
#endif
	/* call board_init_r(gd_t *id, ulong dest_addr) */
	mov     r0, r9                  /* gd_t */
	ldr	r1, [r9, #GD_RELOCADDR]	/* dest_addr */
	/* call board_init_r */
	ldr	pc, =<span style="color:#FF0000;">board_init_r</span>	/* this is auto-relocated! */

	/* we should not return here. */
#endif
 

board/freescale/mx6sabresd下的mx6sabresd.c

void board_init_f(ulong dummy)
{
	/* setup AIPS and disable watchdog */
	arch_cpu_init();

	ccgr_init();
	gpr_init();

	/* iomux and setup of i2c */
	board_early_init_f();

	/* setup GP timer */
	timer_init();

	/* UART clocks enabled and gd valid - init serial console */
	preloader_console_init();

	/* DDR initialization */
	spl_dram_init();

	/* Clear the BSS. */
	memset(__bss_start, 0, __bss_end - __bss_start);

	/* load/boot image from boot device */
	<span style="color:#FF0000;">board_init_r(NULL, 0);</span>
}
 

函式board_init_r(NULL, 0)最終呼叫了common/board_r.c

void board_init_r(gd_t *new_gd, ulong dest_addr)
{
#ifdef CONFIG_NEEDS_MANUAL_RELOC
    int i;
#endif

#ifdef CONFIG_AVR32
    mmu_init_r(dest_addr);
#endif

#if !defined(CONFIG_X86) && !defined(CONFIG_ARM) && !defined(CONFIG_ARM64)
    gd = new_gd;
#endif

#ifdef CONFIG_NEEDS_MANUAL_RELOC
    for (i = 0; i < ARRAY_SIZE(init_sequence_r); i++)
        init_sequence_r[i] += gd->reloc_off;
#endif

    if (initcall_run_list(<span style="color:#FF0000;">init_sequence_r</span>))
        hang();

    /* NOTREACHED - run_main_loop() does not return */
    hang();
}
 

這裡看看陣列init_sequence_r的內容。

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,
#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_NEEDS_MANUAL_RELOC
	initr_manual_reloc_cmdtable,
#endif
#if defined(CONFIG_PPC) || defined(CONFIG_M68K)
	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) || defined(CONFIG_M68K)
	/* 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,
#ifdef CONFIG_SYS_BOOTPARAMS_LEN
	initr_malloc_bootparams,
#endif
	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
	<span style="color:#FF0000;">stdio_add_devices,</span>
	initr_jumptable,
#ifdef CONFIG_API
	initr_api,
#endif
	console_init_r,		/* fully init console as a device */
#ifdef CONFIG_DISPLAY_BOARDINFO_LATE
	show_board_info,
#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) || defined(CONFIG_AVR32)
	initr_enable_interrupts,
#endif
#if defined(CONFIG_X86) || defined(CONFIG_MICROBLAZE) || defined(CONFIG_AVR32) \
	|| defined(CONFIG_M68K)
	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_FSL_FASTBOOT
	initr_fastboot_setup,
#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
#ifdef CONFIG_FSL_FASTBOOT
	initr_check_fastboot,
#endif
	run_main_loop,
};

int stdio_add_devices(void)
{
#ifdef CONFIG_SYS_I2C
	i2c_init_all();
#else
#if defined(CONFIG_HARD_I2C)
	i2c_init (CONFIG_SYS_I2C_SPEED, CONFIG_SYS_I2C_SLAVE);
#endif
#endif
#ifdef CONFIG_LCD
	drv_lcd_init ();
#endif
#if defined(CONFIG_VIDEO) || defined(CONFIG_CFB_CONSOLE)
	<span style="color:#FF0000;">drv_video_init ();</span>
#endif
#ifdef CONFIG_KEYBOARD
	drv_keyboard_init ();
#endif
#ifdef CONFIG_LOGBUFFER
	drv_logbuff_init ();
#endif
	drv_system_init ();
	serial_stdio_init ();
#ifdef CONFIG_USB_TTY
	drv_usbtty_init ();
#endif
#ifdef CONFIG_NETCONSOLE
	drv_nc_init ();
#endif
#ifdef CONFIG_JTAG_CONSOLE
	drv_jtag_console_init ();
#endif
#ifdef CONFIG_CBMEM_CONSOLE
	cbmemc_init();
#endif

	return 0;
}

int drv_video_init(void)
{
	int skip_dev_init;
	struct stdio_dev console_dev;

	/* Check if video initialization should be skipped */
	<span style="color:#FF0000;">if (board_video_skip())</span>
		return 0;

	/* Init video chip - returns with framebuffer cleared */
	<span style="color:#FF0000;">skip_dev_init = (video_init() == -1);</span>

	if (board_cfb_skip())
		return 0;

#if !defined(CONFIG_VGA_AS_SINGLE_DEVICE)
	debug("KBD: Keyboard init ...\n");
	skip_dev_init |= (VIDEO_KBD_INIT_FCT == -1);
#endif

	if (skip_dev_init)
		return 0;

	/* Init vga device */
	memset(&console_dev, 0, sizeof(console_dev));
	strcpy(console_dev.name, "vga");
	console_dev.ext = DEV_EXT_VIDEO;	/* Video extensions */
	console_dev.flags = DEV_FLAGS_OUTPUT | DEV_FLAGS_SYSTEM;
	console_dev.putc = video_putc;	/* 'putc' function */
	console_dev.puts = video_puts;	/* 'puts' function */

#if !defined(CONFIG_VGA_AS_SINGLE_DEVICE)
	/* Also init console device */
	console_dev.flags |= DEV_FLAGS_INPUT;
	console_dev.tstc = VIDEO_TSTC_FCT;	/* 'tstc' function */
	console_dev.getc = VIDEO_GETC_FCT;	/* 'getc' function */
#endif /* CONFIG_VGA_AS_SINGLE_DEVICE */

	if (stdio_register(&console_dev) != 0)
		return 0;

	/* Return success */
	return 1;
}

board_video_skip獲取要初始化的螢幕引數arch/arm/imx-common/video.c

int board_video_skip(void)
{
	int i;
	int ret;
	char const *panel = getenv("panel");

	if (!panel) {
		for (i = 0; i < display_count; i++) {
			struct display_info_t const *dev = displays+i;
			if (dev->detect && dev->detect(dev)) {
				panel = dev->mode.name;
				printf("auto-detected panel %s\n", panel);
				break;
			}
		}
		if (!panel) {
			panel = displays[0].mode.name;
			printf("No panel detected: default to %s\n", panel);
			i = 2;
		}
	} else {
		for (i = 0; i < display_count; i++) {
			if (!strcmp(panel, displays[i].mode.name))
				break;
		}
	}

	if (i < display_count) {
		ret = <span style="color:#FF0000;">ipuv3_fb_init</span>(&displays[i].mode, 0,
				    displays[i].pixfmt);
		if (!ret) {
			if (displays[i].enable)
				displays[i].enable(displays + i);

			printf("Display: %s (%ux%u)\n",
			       displays[i].mode.name,
			       displays[i].mode.xres,
			       displays[i].mode.yres);
		} else
			printf("LCD %s cannot be configured: %d\n",
			       displays[i].mode.name, ret);
	} else {
		printf("unsupported panel %s\n", panel);
		return -EINVAL;
	}

	return 0;

void video_init(void)

{

------

video_hw_init  //螢幕初始化(根據上面獲取到的引數)

video_logo();//刷logo(位於tools/logos/xxx.bmp,該bmp點陣圖被編譯成陣列，最終被刷出來)

------

}

在刷logo的過程中會呼叫flush_cache重新整理一下緩衝區，否則影象會變得離散。

if (cfb_do_flush_cache)
        flush_cache(VIDEO_FB_ADRS, VIDEO_SIZE)；

VIDEO_FB_ADRS顯示基地址

VIDEO_SIZE顯示的大小

在uboot中有很多debug函式，開啟debug函式可以看到uboot中函式的呼叫過程。

dedug函式(include/common.h)的定義為

#ifdef DEBUG
#define _DEBUG	1
#else
#define _DEBUG	0
#endif

#ifndef pr_fmt
#define pr_fmt(fmt) fmt
#endif

/*
 * Output a debug text when condition "cond" is met. The "cond" should be
 * computed by a preprocessor in the best case, allowing for the best
 * optimization.
 */
#define debug_cond(cond, fmt, args...)			\
	do {						\
		if (cond)				\
			printf(pr_fmt(fmt), ##args);	\
	} while (0)

#define debug(fmt, args...)			\
	debug_cond(_DEBUG, fmt, ##args)

只需在前面新增#define DEBUG即可開啟該函式。

       另外,查詢函式呼叫關係時，如果有多個地方被定義，不確定具體的定義位置時，只需到該目錄下，ls -al *.o，即可確認真正被呼叫的函式。

因為該函式被編譯了，就會生成.o檔案。