u-boot启动之第2阶段浅析

??????????在第一阶段分析中已经知道，经过一系列板级初始化后最后是调用函数start_armboot (void)，这个告诉我们第2阶段应该是从这个函数开始进行分析，这个函数是在/lib_arm/board.c文件中。

1. /* Pointer is writable since we allocated a register for it */
2. ?gd = (gd_t*)(_armboot_start - CFG_MALLOC_LEN - sizeof(gd_t));??? //这里的gd_t*是一个结构体的指针，直接给它分配一段内存，在完全手册的图
3. ?/* compiler optimization barrier needed for GCC >= 3.4 */
4. ?__asm__ __volatile__("": : :"memory");
5. ?memset ((void*)gd,sizeof (gd_t));
6. ?gd->bd = (bd_t*)((char*)gd - sizeof(bd_t));???????????????? //分配内存块大小??????????
7. ?memset (gd->bd,sizeof (bd_t));
8. ?monitor_flash_len = _bss_start - _armboot_start;
9. ?for (init_fnc_ptr = init_sequence; *init_fnc_ptr; ++init_fnc_ptr) {?????? //调用函数初始化指针
10. ???????????????? ??if ((*init_fnc_ptr)() != 0)
11. ???????????????????????????? ?{
12. ?????????????????????????????????????? ?????hang ();
13. ??????????????????????????????}

?????????????????????????????????????????????

这个结构体gd_t*在u-boot内存中的指向就是在128? Bytes的内存CFG_GBL_DATA_SIZE。函数init_sequence是一系列函数指针：

1. init_fnc_t *init_sequence[] = {

2. ????????????? ?cpu_init,??/* basic cpu dependent setup */?????????????????????

3. ????????????? ?board_init,??/* basic board dependent setup */???????????????? //单板初始化

4. ???????????????interrupt_init,??/* set up exceptions */

5. ????????????? env_init,??/* initialize environment */??????????????????????????????????? //环境变量初始化

6. ???????????? ?init_baudrate,??/* initialze baudrate settings */

7. ?????????? ? ?serial_init,??/* serial communications setup */

8. ?????????? ?? console_init_f,??/* stage 1 init of console */

9. ???????? ?? ?display_banner,??/* say that we are here */

10. #if defined(CONFIG_DISPLAY_CPUINFO)

11. ????????? ?? print_cpuinfo,??/* display cpu info (and speed) */

12. #endif

比如CPU的初始化就是在cpu/arm920t/cpu.c中：

1. int cpu_init (void)
2. {
3. ?/*
   ? * setup up stacks if necessary
   ? */
4. #ifdef CONFIG_USE_IRQ
5. ??????????? ?IRQ_STACK_START = _armboot_start - CFG_MALLOC_LEN - CFG_GBL_DATA_SIZE - 4;
6. ??????????? ?FIQ_STACK_START = IRQ_STACK_START - CONFIG_STACKSIZE_IRQ;
7. ???????????? FREE_RAM_END = FIQ_STACK_START - CONFIG_STACKSIZE_FIQ - CONFIG_STACKSIZE;
8. ???????????? FREE_RAM_SIZE = FREE_RAM_END - PHYS_SDRAM_1;
9. #else?
   ?
   ????????? ? FREE_RAM_END = _armboot_start - CFG_MALLOC_LEN - CFG_GBL_DATA_SIZE - 4 - CONFIG_STACKSIZE;
10. ????????????FREE_RAM_SIZE = FREE_RAM_END - PHYS_SDRAM_1;
11. #endif
12. ?????????? ?return 0;
13. }

?单板初始化函数?board_init（）就是在board/open24x0/open24x0.c中：

?/*
?* Miscellaneous platform dependent initialisations
?*/

1. int board_init (void)
2. ????????????{
3. ???????????????????????? S3C24X0_CLOCK_POWER * const clk_power = S3C24X0_GetBase_CLOCK_POWER();
4. ?????????????????? ??? ? S3C24X0_GPIO * const gpio = S3C24X0_GetBase_GPIO();
5. ??? /* set up the I/O ports */
6. ??????????????????? ? ? gpio->GPACON = 0x007FFFFF;????? //参考数据手册来设置
7. ????????????????????? ? gpio->GPBCON = 0x00044555;
8. ???????????????????? ?? gpio->GPBUP = 0x000007FF;
9. ????????????????????? ? gpio->GPCCON = 0xAAAAAAAA;
10. ???????????????????? ?? gpio->GPCUP = 0x0000FFFF;
11. ??????????????????? ??? gpio->GPDCON = 0xAAAAAAAA;
12. ????????????????????? ? gpio->GPDUP = 0x0000FFFF;
13. ???????????????????? ?? gpio->GPECON = 0xAAAAAAAA;
14. ?????????????????????? ?gpio->GPEUP = 0x0000FFFF;
15. ??????????????????????? gpio->GPFCON = 0x000055AA;
16. ?????????????????????? ?gpio->GPFUP = 0x000000FF;
17. ?????????????????????? ?gpio->GPGCON = 0xFF95FFBA;
18. ????????????????????? ? gpio->GPGUP = 0x0000FFFF;
19. ????????????????????? ? gpio->GPHCON = 0x002AFAAA;
20. ???????????????????? ?? gpio->GPHUP = 0x000007FF;
21. ??? /* support both of S3C2410 and S3C2440,by www.arm9.net */
22. ????????????????????? ? if ((gpio->GSTATUS1 == 0x32410000) || (gpio->GSTATUS1 == 0x32410002))
23. ?????????????????????????????? ?{
24. ??????? /* arch number of SMDK2410-Board */
25. ??????????????????????????????????????? ? gd->bd->bi_arch_number = MACH_TYPE_SMDK2410;
26. ?????????????????????????????? ? }
27. ??? else
28. ??????????? ??? {
29. ??????? /* arch number of SMDK2440-Board */
30. ?????????????????????? ? gd->bd->bi_arch_number = MACH_TYPE_S3C2440;???????? //arch_number 架构数字就是机器码，显然这个在启动内核时要传递给内核才能正确启动
31. ????????????? ?? }????????????????????????????????????????????????????????????????????????????????????????????????????????????? //否则会有提示start? kernel..........就停在这里不动
32. ??? /* adress of boot parameters */
33. ??????????????????? ??? gd->bd->bi_boot_params = 0x30000100;????????? //启动参数在启动内核时也要传递给内核，0x30000100就是存放地址，内核从这里读取参数
34. ??????????????????? ??? icache_enable();
35. #if 0
    ???????????????????? ?dcache_enable();
    #endif
36. ?????????????????? ?? return 0;
37. ????????????? }

这些寄存器的初化都是跟板级的处理器有非常密切关系，不同的开发板不同处理器一般会有不同的参数，在移植的时候可以借鉴这个思路，参考相关的手册就可以移植。回到我们主题，要想从Nand Flash中读取内核数据，首先是要能够执行读操作，也就是u-boot必须支持读命令这样才能正常读取数据。现在很多的u-boot为了方便开发，在其中加了了可以写的功能函数。

?

2.?? 对Flash 初始化，在Board.c中

1. #ifndef CFG_NO_FLASH
2. ?/* configure available FLASH banks */
3. ?????????????????? ?size = flash_init ();?????????????????????????????????? //对flash的初化函数???????????????????
4. ?????????????????? ?display_flash_config (size);
5. #endif /* CFG_NO_FLASH */

下面的代码是具体的初始化代码，在drivers/cfi_flash.c中：

这个函数可以识别不同的Flash，具体的实现过程参考相关手册。

1. /*-----------------------------------------------------------------------
   ?*/
   unsigned long flash_init (void)
2. ??????????? {
3. ??????????????????? ?unsigned long size = 0;
4. ?????????????????????int i;
5. #ifdef CFG_FLASH_PROTECTION
6. ???????????????????? char *s = getenv("unlock");
7. #endif
8. ?/* Init: no FLASHes known */
9. ?????????????????? ?for (i = 0; i < CFG_MAX_FLASH_BANKS; ++i) {
10. ????????????????? ??flash_info[i].flash_id = FLASH_UNKNOWN;
11. ??????????????????? size += flash_info[i].size = flash_get_size (bank_base[i],i);
12. ??if (flash_info[i].flash_id == FLASH_UNKNOWN) {??????????????????????????? //用于识别不同的Flash
13. #ifndef CFG_FLASH_QUIET_TEST
14. ???printf ("## Unknown FLASH on Bank %d - Size = 0x%08lx = %ld MBn",
    ????i,flash_info[i].size,flash_info[i].size << 20);
15. #endif /* CFG_FLASH_QUIET_TEST */
    ??????????? ??}
    #ifdef CFG_FLASH_PROTECTION
16. ??else if ((s != NULL) && (strcmp(s,"yes") == 0)) {
17. ???/*
    ??? * Only the U-Boot image and it's environment is protected,
    ??? * all other sectors are unprotected (unlocked) if flash
    ??? * hardware protection is used (CFG_FLASH_PROTECTION) and
    ??? * the environment variable "unlock" is set to "yes".
    ??? */
18. ????????????????? ?if (flash_info[i].legacy_unlock) {
19. ???????????????????int k;
20. ????/*
    ???? * Disable legacy_unlock temporarily,since
    ???? * flash_real_protect would relock all other sectors
    ???? * again otherwise.
    ???? */
21. ???????????????? ??flash_info[i].legacy_unlock = 0;
22. ????/*
    ???? * Legacy unlocking (e.g. Intel J3) -> unlock only one
    ???? * sector. This will unlock all sectors.
    ???? */
23. ???????????????? ???flash_real_protect (&flash_info[i],0);
24. ????????????????? ??flash_info[i].legacy_unlock = 1;
25. ????/*
    ???? * Manually mark other sectors as unlocked (unprotected)
    ???? */
26. ????????????????? ??for (k = 1; k < flash_info[i].sector_count; k++)
27. ?????????????????? ?flash_info[i].protect[k] = 0;
28. ???????????????? ???} else {
29. ????/*
    ???? * No legancy unlocking -> unlock all sectors
    ???? */
30. ???????????????????????????????????? ? ??flash_protect (FLAG_PROTECT_CLEAR,
31. ????????????????????????????????????? ?? flash_info[i].start[0],
32. ???????????????????????????????? ??? ??? flash_info[i].start[0] + flash_info[i].size - 1,
33. ???????????????????????????????????????? &flash_info[i]);
34. ???????????????????????????? ???}
35. ??? ??}
36. #endif /* CFG_FLASH_PROTECTION */
37. ????????????? ?}
38. ?/* Monitor protection ON by default */
39. #if (CFG_MONITOR_BASE >= CFG_FLASH_BASE)
40. ???????????????????? ?flash_protect (FLAG_PROTECT_SET,
41. ??????????????????????????? ??? CFG_MONITOR_BASE,
42. ???????????????????????????? ?? CFG_MONITOR_BASE + monitor_flash_len? - 1,
43. ?????????????????????????? ???? flash_get_info(CFG_MONITOR_BASE));
44. #endif
45. ?/* Environment protection ON by default */
46. #ifdef CFG_ENV_IS_IN_FLASH
47. ?????????????????? ?flash_protect (FLAG_PROTECT_SET,
48. ???????????????????????????????CFG_ENV_ADDR,
49. ?????????????????????????????? CFG_ENV_ADDR + CFG_ENV_SECT_SIZE - 1,
50. ???????????????????????????? ? flash_get_info(CFG_ENV_ADDR));
51. #endif
52. ?/* Redundant environment protection ON by default */
53. #ifdef CFG_ENV_ADDR_REDUND
54. ??????????????? ?flash_protect (FLAG_PROTECT_SET,
55. ???????????????????????????? ?CFG_ENV_ADDR_REDUND,
56. ????????????????????????????? CFG_ENV_ADDR_REDUND + CFG_ENV_SIZE_REDUND - 1,
57. ????????????????????????????? ?flash_get_info(CFG_ENV_ADDR_REDUND));
58. #endif
59. ?????????????????????? ?return (size);
60. ????????? }
    

???????????? /* armboot_start is defined in the board-specific linker script */

????????????? ?mem_malloc_init (_armboot_start - CFG_MALLOC_LEN);???????? //这个是给内存分配空间，对应上面内存图中192K字节空间-----CFG_MALLOC_LEN.在这里实现

?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????? //堆空间的分配和释放?

?

?继续往下看：

1. #if (CONFIG_COMMANDS & CFG_CMD_NAND)
2. ?puts ("NAND:? ");
3. ?nand_init();????????????????? ?/* go init the NAND */
4. #endif

nand_init();的具体代码是在drivers/nand/nand.c中，它可以识别在单板中的Nand Flash。

1. void nand_init(void)
2. {
3. ?int i;
4. ?unsigned int size = 0;
5. ?for (i = 0; i < CFG_MAX_NAND_DEVICE; i++) {
6. ??nand_init_chip(&nand_info[i],&nand_chip[i],base_address[i]);
7. ??size += nand_info[i].size;
8. ??if (nand_curr_device == -1)
9. ???nand_curr_device = i;
10. ?}
11. ?printf("%lu MiBn",size / (1024 * 1024));
12. #ifdef CFG_NAND_SELECT_DEVICE
13. ?/*
    ? * Select the chip in the board/cpu specific driver
    ? */
14. ?board_nand_select_device(nand_info[nand_curr_device].priv,nand_curr_device);
15. #endif
16. }

其实我们的u-boot就是通过调用这两个函数flash_init (void)和nand_init(void)来实现对内核的数据的读取的，代码过程可以不用理它，只要把它作为一个接口调用即可。

?

1. #ifdef CONFIG_HAS_DATAFLASH
2. ?AT91F_DataflashInit();
3. ?dataflash_print_info();
4. #endif
5. ?/* initialize environment */
6. ?env_relocate ();?????????????????? //环境变量初始化，一种是在代码中写好了的默认值，一种是在Flash中保存的，这个是修改后的值，启动时先到Flash中看是否有

?????????????????????????????????????????????????????????? //要是有就用最新的环境变量值，没有就用默认的值

?

?

?

下现是网卡和USB等等的一些IP等的初始化：

1. ?/* IP Address */
2. ??????????????? ?gd->bd->bi_ip_addr = getenv_IPaddr ("ipaddr");
3. ?/* MAC Address */
4. ?????????????????????? ?{
5. ????????????????????????????????? ?int i;
6. ??????????????????????????????? ? ?ulong reg;
7. ?????????????????????????????????? char *s,*e;
8. ???????????????????????????????? ??char tmp[64];
9. ???????????????????????????????? ??i = getenv_r ("ethaddr",tmp,sizeof (tmp));
10. ???????????????????????????????? ??s = (i > 0) ? tmp : NULL;
11. ???????????????????????????????? ??for (reg = 0; reg < 6; ++reg) {
12. ????????????????????????????????? gd->bd->bi_enetaddr[reg] = s ? simple_strtoul (s,&e,16) : 0;
13. ???????????????????????????????????if (s)
14. ?????????????????????????????????????????? ??s = (*e) ? e + 1 : e;
15. ????????????????????? ?}
16. #ifdef CONFIG_HAS_ETH1
17. ??????????????????????????????? ?i = getenv_r ("eth1addr",sizeof (tmp));
18. ?????????????????????????????? ??s = (i > 0) ? tmp : NULL;
19. ?????????????????????????????? ??for (reg = 0; reg < 6; ++reg) {
20. ??????????????????????????????? gd->bd->bi_enet1addr[reg] = s ? simple_strtoul (s,16) : 0;
21. ????????????????????????????? ???if (s)
22. ?????????????????????????????????s = (*e) ? e + 1 : e;?????????????????? //网卡的初始化
23. ????????????????????????? ?}
24. #endif
25. ???????????????????? ?}
26. ?????????????????????????????? ?devices_init ();?????????????????????????? /* get the devices list going. */
27. #ifdef CONFIG_CMC_PU2
28. ?????????????????????????????? ?load_sernum_ethaddr ();
29. #endif /* CONFIG_CMC_PU2 */
30. ?????????????????????????????? ?jumptable_init ();
31. ????????????????????????????? ?console_init_r ();??????????????????????????? ?/* fully init console as a device */
32. #if defined(CONFIG_MISC_INIT_R)
33. ?/* miscellaneous platform dependent initialisations */
34. ????????????????????????????? ?misc_init_r ();
35. #endif
36. ????????????????????????????? ?Port_Init();
37. ????????????????????????????? ?if (!PreLoadedONRAM) {????????????????????????? //如果用调试器下载的话这个PreLoadedONRAM被制成1
38. ??/* enable exceptions */
39. ?????????????????????????????? enable_interrupts ();
40. ???? /* add by www.arm9.net */
41. ????????????????????????????? ?usb_init();????????????????????????????????????? //USB设备初始化
42. ?}
43. ??? /* Perform network card initialisation if necessary */
44. #ifdef CONFIG_DRIVER_CS8900
45. ?????????????????????????????? ?cs8900_get_enetaddr (gd->bd->bi_enetaddr);
46. #endif
47. #if defined(CONFIG_DRIVER_SMC91111) || defined (CONFIG_DRIVER_LAN91C96)
48. ????????????????????????????? ?if (getenv ("ethaddr")) {????????????????????????????????????????????????????
49. ????????????????????????????????????? ??smc_set_mac_addr(gd->bd->bi_enetaddr);???????????????? //获取MAC地址
50. ?}
51. #endif /* CONFIG_DRIVER_SMC91111 || CONFIG_DRIVER_LAN91C96 */
52. ?/* Initialize from environment */
53. ????????????????????????????? ?if ((s = getenv ("loadaddr")) != NULL) {
54. ????????????????????????????? ?load_addr = simple_strtoul (s,NULL,16);
55. ?}
56. #if (CONFIG_COMMANDS & CFG_CMD_NET)
57. ???????????????????????????? ?if ((s = getenv ("bootfile")) != NULL) {
58. ??????????????????????????????????? ??copy_filename (BootFile,s,sizeof (BootFile));
59. ?}
60. #endif?/* CFG_CMD_NET */
61. #ifdef BOARD_LATE_INIT
62. ????????????????????????????? ?board_late_init ();
63. #endif
64. #if (CONFIG_COMMANDS & CFG_CMD_NET)
65. #if defined(CONFIG_NET_MULTI)
66. ????????????????????????????? ?puts ("Net:?? ");
67. #endif
68. ????????????????????????????? ?eth_initialize(gd->bd);
69. #endif
70. ?/* main_loop() can return to retry autoboot,if so just run it again. */
71. ?????????????????????????????????for (;;) {
72. ????????????????????????????????????????? ??main_loop ();????????????????????? //最终进入这个C语言函数，进行循环，就像在等待输入命令，一个死循环
73. ?????????????????? ?}
74. ?/* NOTREACHED - no way out of command loop except booting */
    ?????????????????}

经过第二阶段的初始化后，最后进入函数?main_loop ()，这个函数是在/comman/main.c中：

1. #ifdef CONFIG_BOOTCOUNT_LIMIT
2. ?if (bootlimit && (bootcount > bootlimit)) {
3. ???????????? ??printf ("Warning: Bootlimit (%u) exceeded. Using altbootcmd.n",
4. ????????????????????????? ?(unsigned)bootlimit);
5. ???????????? ?s = getenv ("altbootcmd");
6. ?}
7. ?else
8. #endif /* CONFIG_BOOTCOUNT_LIMIT */
9. ????????????? ?s = getenv ("bootcmd");
10. ?debug ("### main_loop: bootcmd="%s"n",s ? s : "<UNDEFINED>");
11. ??????????????????? ?if (bootdelay >= 0 && s && !abortboot (bootdelay)) {?????????????????? //这里是在u-boot启动时有倒数计时，要是没有空格被按下则会跳到其他分支，下面有说明
12. # ifdef CONFIG_AUTOBOOT_KEYED
13. ??????????????????? ??int prev = disable_ctrlc(1);?/* disable Control C checking */
14. # endif
15. # ifndef CFG_HUSH_PARSER
16. #ifdef CONFIG_SURPORT_WINCE
17. ??????? if (!TOC_Read())
18. ???????????????? ?? {
19. ?????????????????????? ?? /* Launch wince */
20. ????????????????????????? ?? char cmd_buf[16];
21. ???????????????????????? ??? printf("Booting wince ...n");
    ??????????
    ??????????????????????????? ?strcpy(cmd_buf,"wince");
22. ??????????????????????? ??? run_command(cmd_buf,0);
23. ??????? }
24. ??????? else
25. #endif
26. ??????? {
27. ??????????? printf("Booting Linux ...n");??
    ????????
    ??? ???? run_command (s,0);
28. ??????? }
29. # else
30. ?????????? ?parse_string_outer(s,FLAG_PARSE_SEMICOLON |
31. ??????????????????? ? FLAG_EXIT_FROM_LOOP);
32. # endif
33. # ifdef CONFIG_AUTOBOOT_KEYED
34. ?????????????????? ?disable_ctrlc(prev);?/* restore Control C checking */
    # endif
35. ?}
36. # ifdef CONFIG_MENUKEY
37. ??????????????????? ?if (menukey == CONFIG_MENUKEY) {????????????????????? //要是空格被按下程序就会跳到这里来执行
38. ??????????????????????????? ?s = getenv("menucmd");
39. ?????????????????????? ??? if (s) {
40. # ifndef CFG_HUSH_PARSER
41. ???????????????????????????????????????????? ??run_command (s,0);
42. # else
43. ????????????????????????????????? ??parse_string_outer(s,FLAG_PARSE_SEMICOLON |
44. ???????????????????????????????? ?? FLAG_EXIT_FROM_LOOP);
45. # endif
46. ???????? ?? }
47. ??}
48. #endif /* CONFIG_MENUKEY */
49. #endif?/* CONFIG_BOOTDELAY */
50. #ifdef CONFIG_AMIGAONEG3SE
51. ?????????? ?{
    ??????????????????????? extern void video_banner(void);
52. ?????????????????????? ?video_banner();
53. ?}
54. #endif
55. ??????????????????? ?? run_command("menu",0);??????????? //u-boot启动时按下空格键时有个菜单的原因就是执行了这个函数
    ?/*
    ? * Main Loop for Monitor Command Processing
    ? */
56. 
    PROMPT:
57. #ifdef CFG_HUSH_PARSER
58. ??????????????? ?parse_file_outer();
59. ?/* This point is never reached */
60. ??????????????? ?for (;;);??????????????????????? //进入菜单后又是一个死循环，等待输入命令，有命令输入后它就会解析命令，没有则显示异常提示信息，因此命令就是u-boot的核心
61. #else
62. ?????????????? ?for (;;) {
63. #ifdef CONFIG_BOOT_RETRY_TIME
64. ????????????? ??if (rc >= 0) {
65. ???/* Saw enough of a valid command to
    ??? * restart the timeout.
    ??? */
66. ???????????????????????? ??reset_cmd_timeout();
67. ??}
68. #endif
69. ??????????????????????? ??len = readline (CFG_PROMPT);
70. 
    ??????????????????????? ??flag = 0;?/* assume no special flags for now */
71. ???????????????????????????if (len > 0)
72. ?????????????????????????????????????? ?strcpy (lastcommand,console_buffer);
73. ????????????????????????????????????? ??else if (len == 0)
74. ????????????????????????????????????????????? ???flag |= CMD_FLAG_REPEAT;
75. #ifdef CONFIG_BOOT_RETRY_TIME
76. ???????????????????????????????????? ??else if (len == -2) {
77. ???/* -2 means timed out,retry autoboot
    ??? */
78. ???????????????????????????????????? ???puts ("nTimed out waiting for commandn");
79. # ifdef CONFIG_RESET_TO_RETRY
80. ???/* Reinit board to run initialization code again */
81. ????????????????????????????????????? ?do_reset (NULL,NULL);
82. # else
83. ???????????????????????????????????? ??return;??/* retry autoboot */
84. # endif
85. ??}
86. #endif
87. ??????????????????????????????????? ??if (len == -1)
88. ???????????????????????????????????????????? ??puts ("<INTERRUPT>n");
89. ??else
90. ???????????????????????????????????????????? ??rc = run_command (lastcommand,flag);
91. 
    ???????????????????????????????????? ?if (rc <= 0) {
92. ???/* invalid command or not repeatable,forget it */
93. ?????????????????????????????????????????????? ??lastcommand[0] = 0;
94. ???????????? ??}
95. ??? ?}
96. #endif /*CFG_HUSH_PARSER*/
97. }
98. #ifdef CONFIG_BOOT_RETRY_TIME

到这里总结一下启动内核是如何调用相关函数的：1.????s = getenv ("altbootcmd");获取环境变量参数

??????????????????????????????????????????????????????????????????????????????????????? 2.????调用?run_command (s,0);函数

?

而在u-boot的控制界面时：1.?? 调用readline（）函数，读取串口数据

??????????????????????????????????????????????? 2.?? 还是调用?run_command (s,0);函数

?

?

在common/main.c中readline()函数代码如下：

/****************************************************************************/

1. /*
   ?* Prompt for input and read a line.
   ?* If? CONFIG_BOOT_RETRY_TIME is defined and retry_time >= 0,
   ?* time out when time goes past endtime (timebase time in ticks).
   ?* Return:?number of read characters
   ?*??-1 if break
   ?*??-2 if timed out
   ?*/
   int readline (const char *const prompt)
2. ???????????? {
3. #ifdef CONFIG_CMDLINE_EDITING
4. ???????????????????????? ?char *p = console_buffer;
5. ???????????????????????? ?unsigned int len=MAX_CMDBUF_SIZE;
6. ??????????????????????????int rc;
7. ???????????????????????? ?static int initted = 0;
8. ???????????????????????? ?if (!initted) {
9. ???????????????????????????????? ??hist_init();
10. ???????????????????????????????????initted = 1;
11. ????????????????????????????????????????????? ?}
12. ???????????????????????? ?puts (prompt);
13. ???????????????????????? ?rc = cread_line(p,&len);
14. ???????????????????????? ?return rc < 0 ? rc : len;
    #else
15. ??????????????????????? ?char?? *p = console_buffer;
16. ???????????????????????? ?int?n = 0;????/* buffer index??*/
17. ??????????????????????? ?int?plen = 0;???/* prompt length?*/
18. ??????????????????????? ?int?col;????/* output column cnt?*/
19. ?????????????????????????char?c;
20. ?/* print prompt */
21. ?????????????????????? ?if (prompt) {
22. ?????????????????????????????? ??plen = strlen (prompt);
23. ?????????????????????????????? ??puts (prompt);
24. ??????????????????????????????????????????? ?}
25. ?????????? ?col = plen;
26. ?????????????for (;;) {
27. #ifdef CONFIG_BOOT_RETRY_TIME
28. ???????????????while (!tstc()) {?/* while no incoming data */
29. ????????????????if (retry_time >= 0 && get_ticks() > endtime)
30. ?????????????????????? ??return (-2);?/* timed out */
31. ????????????????????????????????????? ??}
32. #endif
33. ??????????????????WATCHDOG_RESET();??/* Trigger watchdog,if needed */
34. 
    #ifdef CONFIG_SHOW_ACTIVITY
35. ?????????????? ??while (!tstc()) {
36. ???????????? ???extern void show_activity(int arg);
37. ?????????????? ??show_activity(0);
38. ??}
39. #endif
40. ?????????????? ?c = getc();
41. ??/*
    ?? * Special character handling
    ?? */
42. ????????????? switch (c) {
43. ????????????????????????????????? ?case 'r':????/* Enter??*/
44. ??????????????????????????????? ??case 'n':
45. ??????????????????????????????? ??*p = '';
46. ????????????????????????????? ???puts ("rn");
47. ?????????????????????????????? ??return (p - console_buffer);
48. ????????????????????case '':????????????????????????????????????? ?/* nul???*/
49. ???????????????? ????????????? ??continue;
50. ?????????????????????????????? ??case 0x03:
    ????/* ^C - break??*/
51. ??????????????????????????? ? ??console_buffer[0] = '';?????????????????????? /* discard input */
52. ??????????????????????????? ???return (-1);
53. ???????????????? ??case 0x15:
    ????/* ^U - erase line?*/
    ????????????????????????????? ??while (col > plen) {
54. ??????????????????????????? ????puts (erase_seq);
55. ?????????????????????????????????--col;
56. ??? ???}
57. ???????????????????????????? ??p = console_buffer;
58. ???????????????????????????????n = 0;
59. ??????????????????????????? ???continue;
60. ?????????????? ??case 0x17:
    ?
    ???/* ^W - erase word ?*/
    ?????????????????????????? ???p=delete_char(console_buffer,p,&col,&n,plen);
61. ???????????????????????????? ??while ((n > 0) && (*p != ' ')) {
62. ??????????????????????????? ??p=delete_char(console_buffer,plen);
63. ???}
64. ????????????????????????? ???continue;
65. ?????????????? ??case 0x08:
    ????/* ^H? - backspace?*/
66. ????????????? ??case 0x7F:????/* DEL - backspace?*/
67. ??????????????????????????? ?p=delete_char(console_buffer,plen);
68. ??????????????????????????? ?continue;
69. ???????????????????????????? ?default:
70. ???/*
    ??? * Must be a normal character then
    ??? */
71. ?????????????? ??if (n < CFG_CBSIZE-2) {
72. ?????????????????????? ??if (c == 't') {???????????????????????????????????????? ?/* expand TABs??*/
73. #ifdef CONFIG_AUTO_COMPLETE
    ?????/* if auto completion triggered just continue */
74. ?????*p = '';
75. ??????????????????????????????????????? ?if (cmd_auto_complete(prompt,console_buffer,&col)) {
76. ????????????????????????????????????????????????? ???p = console_buffer + n;?????????????????????????????????????????? ?/* reset */
77. ???????????????????????????????????????????????? ?????continue;
78. ?????}
79. #endif
80. ????????????????????????????????????? ?puts (tab_seq+(col&07));
81. ????????????????????????????????????? ?col += 8 - (col&07);
82. ????} else {
83. ???????????????????????????????????? ??++col;???????????????????????????????????????? ??/* echo input??*/
84. ???????????????????????????????????? ???putc (c);
85. ????}
86. ?????????????????????????????????????? ?*p++ = c;
87. ????????????????????????????????????? ???++n;
88. ?????????????????????????????????????? ??} else {???/* Buffer full??*/
89. ???????????????????????????????????? ???putc ('a');
90. ???}
91. ??}
92. ?}
93. #endif /* CONFIG_CMDLINE_EDITING */
94. }

?

?参考韦东山老师的视频教程！