UBOOT stage2 board_init_r();函数到引导内核流程

转载 ： http://blog.csdn.net/u014381531/article/details/52062257

本人用的是friendlyarm smart4418的板子，用的也是从其github clone下来的uboot-nanopi2的源码，感觉这个uboot特别的复杂，跟网上很多其余板子的教程有很多地方不同，此篇博客是学习的一点记录，欢迎广大网友指正。

上面的一篇博客给了很大帮助，也有别的很多优秀的博客，就没有一一列举。

UBOOT分为两个阶段，第一个阶段主要是汇编代码在START.S文件中实现。在stage1的最后初始化堆栈等操作为stage2C语言的运行提供了环境，最后程序跳入C语言。

ldr	sp, =(CONFIG_SYS_INIT_SP_ADDR)
	bic	sp, sp, #7					/* 8-byte alignment for ABI compliance */
	sub	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	r0, #0
	bl	board_init_f

	mov	sp, r9						/* SP is GD's base address */
	bic	sp, sp, #7					/* 8-byte alignment for ABI compliance */
	sub	sp, #GENERATED_BD_INFO_SIZE	/* allocate one BD above SP */
	bic	sp, sp, #7					/* 8-byte alignment for ABI compliance */

	mov	r0, r9						/* gd_t *gd */
	ldr r1, TEXT_BASE				/* ulong text */
	mov r2, sp						/* ulong sp */
	bl	gdt_reset

	/* call board_init_r(gd_t *id, ulong dest_addr) */
	mov	r0, r9							/* gd_t */
	ldr	r1,  =(CONFIG_SYS_MALLOC_END)	/* dest_addr for malloc heap end */
	/* call board_init_r */
	ldr	pc, =board_init_r				/* this is auto-relocated! */

#else	/* CONFIG_RELOC_TO_TEXT_BASE */

	bl	_main
#endif

上图是我所用的uboot-nanopi2下arch/arm/cpu/slsip/s5p4418/start.s文件，跟网上的很多教程相比很相似，但是细究起来差别也蛮大的，就上面的代码来说，在擦除了bss后设置可sp指针，然后就跳入board_init_f();函数，在board_init.f函数里面，完成了一系列初始化后再调回来。gdt_reset进行gd结构体的初始化，最后进入到了board_init_r();函数，这个函数就是最后载入内核或者开始uboot命令行的操作。

board_init_f();board_init_r();函数在arch/arm/lib/目录下，board_init_r();函数的一系列初始化操作就不说了，因为我也还没有弄懂具体的初始化机制和原由，直奔主题-------怎么进去的内核。

下图是我粘贴的board_init_r();的完整内容，可以直接略过。

/************************************************************************
 *
 * This is the next part if the initialization sequence: we are now
 * running from RAM and have a "normal" C environment, i. e. global
 * data can be written, BSS has been cleared, the stack size in not
 * that critical any more, etc.
 *
 ************************************************************************
 */

void board_init_r(gd_t *id, ulong dest_addr)
{
	ulong malloc_start;
#if !defined(CONFIG_SYS_NO_FLASH)
	ulong flash_size;
#endif

	gd->flags |= GD_FLG_RELOC;	/* tell others: relocation done */
	bootstage_mark_name(BOOTSTAGE_ID_START_UBOOT_R, "board_init_r");

	monitor_flash_len = (ulong)&__rel_dyn_end - (ulong)_start;

	/* Enable caches */
	enable_caches();

	debug("monitor flash len: %08lX\n", monitor_flash_len);
	board_init();	/* Setup chipselects */
	/*
	 * 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
	serial_initialize();

	debug("Now running in RAM - U-Boot at: %08lx\n", dest_addr);

#ifdef CONFIG_LOGBUFFER
	logbuff_init_ptrs();
#endif
#ifdef CONFIG_POST
	post_output_backlog();
#endif

	/* The Malloc area is immediately below the monitor copy in DRAM */
	malloc_start = dest_addr - TOTAL_MALLOC_LEN;
	mem_malloc_init (malloc_start, TOTAL_MALLOC_LEN);

#ifdef CONFIG_ARCH_EARLY_INIT_R
	arch_early_init_r();
#endif

#ifndef CONFIG_PMIC_REG_DUMP
	power_init_board();
#endif

#if !defined(CONFIG_SYS_NO_FLASH)
	puts("Flash: ");

	flash_size = flash_init();
	if (flash_size > 0) {
# ifdef CONFIG_SYS_FLASH_CHECKSUM
		print_size(flash_size, "");
		/*
		 * Compute and print flash CRC if flashchecksum is set to 'y'
		 *
		 * NOTE: Maybe we should add some WATCHDOG_RESET()? XXX
		 */
		if (getenv_yesno("flashchecksum") == 1) {
			printf("  CRC: %08X", crc32(0,
				(const unsigned char *) CONFIG_SYS_FLASH_BASE,
				flash_size));
		}
		putc('\n');
# else	/* !CONFIG_SYS_FLASH_CHECKSUM */
		print_size(flash_size, "\n");
# endif /* CONFIG_SYS_FLASH_CHECKSUM */
	} else {
		puts(failed);
		hang();
	}
#endif

#if defined(CONFIG_CMD_NAND)
#if defined(CONFIG_NAND_MTD)
	puts("NAND:  ");
	nand_init();		/* go init the NAND */
#elif defined(CONFIG_NAND_FTL)
#include 
	puts("NAND FTL:  ");
	nand_ftl_init();		/* go init the NAND */
#endif
#endif /* CONFIG_CMD_NAND */

#if defined(CONFIG_CMD_ONENAND)
	onenand_init();
#endif

#ifdef CONFIG_GENERIC_MMC
	puts("MMC:   ");
	mmc_initialize(gd->bd);
#endif

#ifdef CONFIG_CMD_SCSI
	puts("SCSI:  ");
	scsi_init();
#endif

#ifdef CONFIG_HAS_DATAFLASH
	AT91F_DataflashInit();
	dataflash_print_info();
#endif

	/* initialize environment */
	if (should_load_env())
		env_relocate();
	else
		set_default_env(NULL);

#if defined(CONFIG_CMD_PCI) || defined(CONFIG_PCI)
	arm_pci_init();
#endif

	stdio_init();	/* get the devices list going. */

	jumptable_init();

#if defined(CONFIG_API)
	/* Initialize API */
	api_init();
#endif

	console_init_r();	/* fully init console as a device */

#ifdef CONFIG_PMIC_REG_DUMP
	power_init_board();
#endif

#ifdef CONFIG_DISPLAY_BOARDINFO_LATE
# ifdef CONFIG_OF_CONTROL
	/* Put this here so it appears on the LCD, now it is ready */
	display_fdt_model(gd->fdt_blob);
# else
	checkboard();
# endif
#endif

#if defined(CONFIG_ARCH_MISC_INIT)
	/* miscellaneous arch dependent initialisations */
	arch_misc_init();
#endif
#if defined(CONFIG_MISC_INIT_R)
	/* miscellaneous platform dependent initialisations */
	misc_init_r();
#endif

	 /* set up exceptions */
	interrupt_init();
	/* enable exceptions */
	enable_interrupts();

	/* Initialize from environment */
	load_addr = getenv_ulong("loadaddr", 16, load_addr);

#ifdef CONFIG_BOARD_LATE_INIT
	board_late_init();
#endif

#ifdef CONFIG_BITBANGMII
	bb_miiphy_init();
#endif
#if defined(CONFIG_CMD_NET)
	puts("Net:   ");
	eth_initialize(gd->bd);
#if defined(CONFIG_RESET_PHY_R)
	debug("Reset Ethernet PHY\n");
	reset_phy();
#endif
#endif

#ifdef CONFIG_POST
	post_run(NULL, POST_RAM | post_bootmode_get(0));
#endif

#if defined(CONFIG_PRAM) || defined(CONFIG_LOGBUFFER)
	/*
	 * Export available size of memory for Linux,
	 * taking into account the protected RAM at top of memory
	 */
	{
		ulong pram = 0;
		uchar memsz[32];

#ifdef CONFIG_PRAM
		pram = getenv_ulong("pram", 10, CONFIG_PRAM);
#endif
#ifdef CONFIG_LOGBUFFER
#ifndef CONFIG_ALT_LB_ADDR
		/* Also take the logbuffer into account (pram is in kB) */
		pram += (LOGBUFF_LEN + LOGBUFF_OVERHEAD) / 1024;
#endif
#endif
		sprintf((char *)memsz, "%ldk", (gd->ram_size / 1024) - pram);
		setenv("mem", (char *)memsz);
	}
#endif

	/* main_loop() can return to retry autoboot, if so just run it again. */
	for (;;) {
		main_loop();
	}

	/* NOTREACHED - no way out of command loop except booting */
}

200多行其实有关的只有这个main_loop();循环。

main_loop();循环：

/* We come here after U-Boot is initialised and ready to process commands */
void main_loop(void)
{
	const char *s;

	bootstage_mark_name(BOOTSTAGE_ID_MAIN_LOOP, "main_loop");

#ifndef CONFIG_SYS_GENERIC_BOARD
	puts("Warning: Your board does not use generic board. Please read\n");
	puts("doc/README.generic-board and take action. Boards not\n");
	puts("upgraded by the late 2014 may break or be removed.\n");
#endif

	modem_init();
#ifdef CONFIG_VERSION_VARIABLE
	setenv("ver", version_string);  /* set version variable */
#endif /* CONFIG_VERSION_VARIABLE */

	cli_init();

	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);

	autoboot_command(s);

	cli_loop();
}

autoboot_command(s);

void autoboot_command(const char *s)
{
	debug("### main_loop: bootcmd=\"%s\"\n", s ? s : "");

	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 */
}

我把编译指令都用黄色去掉，发现剩下的就是一个abortboot();这个函数比较有用。

abortboot();

static int abortboot(int bootdelay)
{
#ifdef CONFIG_AUTOBOOT_KEYED
	return abortboot_keyed(bootdelay);
#else
	return abortboot_normal(bootdelay);
#endif
}

abortboot_normal();

static int abortboot_normal(int bootdelay)
{
	int abort = 0;
	unsigned long ts;

#ifdef CONFIG_MENUPROMPT
	printf(CONFIG_MENUPROMPT);
#else
	if (bootdelay >= 0)
		printf("Hit any key to stop autoboot: %2d ", bootdelay);
#endif

#if defined CONFIG_ZERO_BOOTDELAY_CHECK
	/*
	 * Check if key already pressed
	 * Don't check if bootdelay < 0
	 */
	if (bootdelay >= 0) {
		if (tstc()) {	/* we got a key press	*/
			(void) getc();  /* consume input	*/
			puts("\b\b\b 0");
			abort = 1;	/* don't auto boot	*/
		}
	}
#endif

	while ((bootdelay > 0) && (!abort)) {
		--bootdelay;
		/* delay 1000 ms */
		ts = get_timer(0);
		do {
			if (tstc()) {	/* we got a key press	*/
				abort  = 1;	/* don't auto boot	*/
				bootdelay = 0;	/* no more delay	*/
# ifdef CONFIG_MENUKEY
				menukey = getc();
# else
				(void) getc();  /* consume input	*/
# endif
				break;
			}
			udelay(10000);
		} while (!abort && get_timer(ts) < 1000);

		printf("\b\b\b%2d ", bootdelay);
	}

	putc('\n');

#ifdef CONFIG_SILENT_CONSOLE
	if (abort)
		gd->flags &= ~GD_FLG_SILENT;
#endif

	return abort;
}

这个函数里面重要的都用红色标出，其中tstc();函数是查询串口的接收标志位，每次buf中收到数据（对应着如果你在这时候按下了某个按键）从而打断uboot自动加载内核从而进入command line模式。

假设没有按键，让其启动内核。这时候函数返回，执行run_command_list();函数。

int run_command_list(const char *cmd, int len, int flag)
{
	int need_buff = 1;
	char *buff = (char *)cmd;	/* cast away const */
	int rcode = 0;

	if (len == -1) {
		len = strlen(cmd);
#ifdef CONFIG_SYS_HUSH_PARSER
		/* hush will never change our string */
		need_buff = 0;
#else
		/* the built-in parser will change our string if it sees \n */
		need_buff = strchr(cmd, '\n') != NULL;
#endif
	}
	if (need_buff) {
		buff = malloc(len + 1);
		if (!buff)
			return 1;
		memcpy(buff, cmd, len);
		buff[len] = '\0';
	}
#ifdef CONFIG_SYS_HUSH_PARSER
	rcode = parse_string_outer(buff, FLAG_PARSE_SEMICOLON);
#else
	/*
	 * This function will overwrite any \n it sees with a \0, which
	 * is why it can't work with a const char *. Here we are making
	 * using of internal knowledge of this function, to avoid always
	 * doing a malloc() which is actually required only in a case that
	 * is pretty rare.
	 */
	rcode = cli_simple_run_command_list(buff, flag);
	if (need_buff)
		free(buff);
#endif

	return rcode;
}

cli_simple_run_command_list();

int cli_simple_run_command_list(char *cmd, int flag)
{
	char *line, *next;
	int rcode = 0;

	/*
	 * Break into individual lines, and execute each line; terminate on
	 * error.
	 */
	next = cmd;
	line = cmd;
	while (*next) {
		if (*next == '\n') {
			*next = '\0';
			/* run only non-empty commands */
			if (*line) {
				debug("** exec: \"%s\"\n", line);
				if (cli_simple_run_command(line, 0) < 0) {
					rcode = 1;
					break;
				}
			}
			line = next + 1;
		}
		++next;
	}
	if (rcode == 0 && *line)
		rcode = (cli_simple_run_command(line, 0) < 0);

	return rcode;
}

cli_simple_run_command();

/*
 * WARNING:
 *
 * We must create a temporary copy of the command since the command we get
 * may be the result from getenv(), which returns a pointer directly to
 * the environment data, which may change magicly when the command we run
 * creates or modifies environment variables (like "bootp" does).
 */
int cli_simple_run_command(const char *cmd, int flag)
{
	char cmdbuf[CONFIG_SYS_CBSIZE];	/* working copy of cmd		*/
	char *token;			/* start of token in cmdbuf	*/
	char *sep;			/* end of token (separator) in cmdbuf */
	char finaltoken[CONFIG_SYS_CBSIZE];
	char *str = cmdbuf;
	char *argv[CONFIG_SYS_MAXARGS + 1];	/* NULL terminated	*/
	int argc, inquotes;
	int repeatable = 1;
	int rc = 0;

	debug_parser("[RUN_COMMAND] cmd[%p]=\"", cmd);
	if (DEBUG_PARSER) {
		/* use puts - string may be loooong */
		puts(cmd ? cmd : "NULL");
		puts("\"\n");
	}
	clear_ctrlc();		/* forget any previous Control C */

	if (!cmd || !*cmd)
		return -1;	/* empty command */

	if (strlen(cmd) >= CONFIG_SYS_CBSIZE) {
		puts("## Command too long!\n");
		return -1;
	}

	strcpy(cmdbuf, cmd);

	/* Process separators and check for invalid
	 * repeatable commands
	 */

	debug_parser("[PROCESS_SEPARATORS] %s\n", cmd);
	while (*str) {
		/*
		 * Find separator, or string end
		 * Allow simple escape of ';' by writing "\;"
		 */
		for (inquotes = 0, sep = str; *sep; sep++) {
			if ((*sep == '\'') &&
			    (*(sep - 1) != '\\'))
				inquotes = !inquotes;

			if (!inquotes &&
			    (*sep == ';') &&	/* separator		*/
			    (sep != str) &&	/* past string start	*/
			    (*(sep - 1) != '\\'))	/* and NOT escaped */
				break;
		}

		/*
		 * Limit the token to data between separators
		 */
		token = str;
		if (*sep) {
			str = sep + 1;	/* start of command for next pass */
			*sep = '\0';
		} else {
			str = sep;	/* no more commands for next pass */
		}
		debug_parser("token: \"%s\"\n", token);

		/* find macros in this token and replace them */
		process_macros(token, finaltoken);

		/* Extract arguments */
		argc = cli_simple_parse_line(finaltoken, argv);
		if (argc == 0) {
			rc = -1;	/* no command at all */
			continue;
		}

		if (cmd_process(flag, argc, argv, &repeatable, NULL))
			rc = -1;

		/* Did the user stop this? */
		if (had_ctrlc())
			return -1;	/* if stopped then not repeatable */
	}

	return rc ? rc : repeatable;
}

cmd_process();

enum command_ret_t cmd_process(int flag, int argc, char * const argv[],
			       int *repeatable, ulong *ticks)
{
	enum command_ret_t rc = CMD_RET_SUCCESS;
	cmd_tbl_t *cmdtp;

	/* Look up command in command table */
	cmdtp = find_cmd(argv[0]);
	if (cmdtp == NULL) {
		printf("Unknown command '%s' - try 'help'\n", argv[0]);
		return 1;
	}

	/* found - check max args */
	if (argc > cmdtp->maxargs)
		rc = CMD_RET_USAGE;

#if defined(CONFIG_CMD_BOOTD)
	/* avoid "bootd" recursion */
	else if (cmdtp->cmd == do_bootd) {
		if (flag & CMD_FLAG_BOOTD) {
			puts("'bootd' recursion detected\n");
			rc = CMD_RET_FAILURE;
		} else {
			flag |= CMD_FLAG_BOOTD;
		}
	}
#endif

	/* If OK so far, then do the command */
	if (!rc) {
		if (ticks)
			*ticks = get_timer(0);
		rc = cmd_call(cmdtp, flag, argc, argv);
		if (ticks)
			*ticks = get_timer(*ticks);
		*repeatable &= cmdtp->repeatable;
	}
	if (rc == CMD_RET_USAGE)
		rc = cmd_usage(cmdtp);
	return rc;
}

cmd_call();

/**
 * Call a command function. This should be the only route in U-Boot to call
 * a command, so that we can track whether we are waiting for input or
 * executing a command.
 *
 * @param cmdtp		Pointer to the command to execute
 * @param flag		Some flags normally 0 (see CMD_FLAG_.. above)
 * @param argc		Number of arguments (arg 0 must be the command text)
 * @param argv		Arguments
 * @return 0 if command succeeded, else non-zero (CMD_RET_...)
 */
static int cmd_call(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
{
	int result;

	result = (cmdtp->cmd)(cmdtp, flag, argc, argv);
	if (result)
		debug("Command failed, result=%d", result);
	return result;
}

到了这里应该算是结束了。。。下图就是cmd_tbl_s结构体，这个结构体定义了uboot能够识别并且执行的命令，其中包括了name,maxargs,(*cmd）其中cmd就是指令对应处理函数的指针。

struct cmd_tbl_s {
	char		*name;		/* Command Name			*/
	int		maxargs;	/* maximum number of arguments	*/
	int		repeatable;	/* autorepeat allowed?		*/
					/* Implementation function	*/
	int		(*cmd)(struct cmd_tbl_s *, int, int, char * const []);
	char		*usage;		/* Usage message	(short)	*/
#ifdef	CONFIG_SYS_LONGHELP
	char		*help;		/* Help  message	(long)	*/
#endif
#ifdef CONFIG_AUTO_COMPLETE
	/* do auto completion on the arguments */
	int		(*complete)(int argc, char * const argv[], char last_char, int maxv, char *cmdv[]);
#endif
};

typedef struct cmd_tbl_s	cmd_tbl_t;

加载内核用的是do_bootm命令，可以查到对应的cmd_tbl_s结构。

到了这里就算是完成了这些工作。