1.看下開發板介紹

1 品牌: 天嵌
2 CPU型號: NXP i.MX6Q
3 架構: Cortex_A9
4 主頻: 4*1GHz
5 內存: 2GB DDR3
6 存儲: 8GB eMMC FLA（64GB可擴）

2. 看下相關驅動啥的。

3. 看下資料的下載，在淘寶找的

4. 看下uboot的源碼，根據手冊是

1 ./build_sh 編譯

5. 是的，你比較厲害，-j8用8個線程去編譯。

1 export ARCH=arm
2 export CROSS_COMPILE=arm-linux-
3 make mx6q_sabresd_android_config
4 make -j8

6. 找到mx6q_sabresd_android_config，沒搞明白，2個make可以放在一起？打開IMX6_CoreC_CD\Linux 源碼包\uboot源碼\uboot_IMX6_CoreC_1.3.4_for_Linux\Makefile

1 mx6q_sabresd_config            2 mx6q_sabresd_android_config             3 mx6q_sabresd_mfg_config            4 mx6q_sabresd_iram_config    : unconfig
5     @[ -z "$(findstring iram_,$@)" ] || 6         { echo "TEXT_BASE = 0x00907000" >$(obj)board/freescale/mx6q_sabresd/config.tmp ; 7           echo "... with iram configuration" ; 8         }
9     @$(MKCONFIG) $(@:_config=) arm arm_cortexa8 mx6q_sabresd freescale mx6

7. 上面的幾個參數，arm是構架 arm_cortexa8是CPU型號 mx6q_sabresd是板子的型號 freescale mx6

8. 找到鏈接文件uboot_IMX6_CoreC_1.3.4_for_Linux\board\freescale\mx6q_sabresd\u-boot.lds

 1 OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
 2 OUTPUT_ARCH(arm)
 3 ENTRY(_start)
 4 SECTIONS
 5 {
 6     . = 0x00000000;  //放置的起始位置
 7 
 8     . = ALIGN(4); //4字節對齊
 9     .text       :   //代碼段
10     {
11       /* WARNING - the following is hand-optimized to fit within    */
12       /* the sector layout of our flash chips!    XXX FIXME XXX    */
13       board/freescale/mx6q_sabresd/flash_header.module    (.text.flasheader)  //天嵌定制？
14       cpu/arm_cortexa8/start.o //啟動文件
15       board/freescale/mx6q_sabresd/libmx6q_sabresd.a    (.text)
16       lib_arm/libarm.a        (.text)
17       net/libnet.a            (.text)
18       drivers/mtd/libmtd.a        (.text)
19       drivers/mmc/libmmc.a        (.text)
20 
21       . = DEFINED(env_offset) ? env_offset : .;
22       common/env_embedded.o(.text)
23 
24       *(.text)
25     }
26 
27     . = ALIGN(4);  //只讀數據段,ROM
28     .rodata : { *(SORT_BY_ALIGNMENT(SORT_BY_NAME(.rodata*))) }
29 
30     . = ALIGN(4); //數據段
31     .data : { *(.data) }
32 
33     . = ALIGN(4);
34     .got : { *(.got) }
35 
36     . = .;
37     __u_boot_cmd_start = .;
38     .u_boot_cmd : { *(.u_boot_cmd) }
39     __u_boot_cmd_end = .;
40 
41     . = ALIGN(4);
42     _end_of_copy = .; /* end_of ROM copy code here */
43 
44     /* Extend to align to 0x1000, then put the Hab Data */
45     . = ALIGN(0x1000);
46     __hab_data = .;
47     . = . + 0x2000;
48     __data_enc_key = .;
49     /* actually, only 64bytes are needed, but this generates
50         a size multiple of 512bytes, which is optimal for SD boot */
51     . = . + 0x200;
52     __hab_data_end = .;
53     /* End of Hab Data, Place it before BSS section */
54 
55     __bss_start = .;
56     .bss : { *(.bss) }
57     _end = .;
58 }

9. 第一行，這個不清楚是啥，天嵌定制的？

board/freescale/mx6q_sabresd/flash_header.module    (.text.flasheader)

10.第2個鏈接的文件是start.c

#include <config.h>
#include <version.h>

.globl _start  //定義一個全局可見的變量
_start: b    reset  //問題，哪裏算是_start的結束？下一個冒號的位置
    ldr    pc, _undefined_instruction  //未定義指令
    ldr    pc, _software_interrupt //軟件中斷向量
    ldr    pc, _prefetch_abort //預取指令中斷向量
    ldr    pc, _data_abort//數據操作異常向量
    ldr    pc, _not_used /、未使用
    ldr    pc, _irq//慢速中斷向量
    ldr    pc, _fiq//快速中斷向量

_undefined_instruction: .word undefined_instruction
_software_interrupt:    .word software_interrupt
_prefetch_abort:    .word prefetch_abort
_data_abort:        .word data_abort
_not_used:        .word not_used
_irq:            .word irq
_fiq:            .word fiq
_pad:            .word 0x12345678 /* now 16*4=64 */
.global _end_vect
_end_vect:

11. 上面的.wordirq說是是什麽意思，點是什麽意思？加點的是偽指令，不會被編譯的，理解如下.word是一個匯編偽指令，表示是一個字節，.word是偽操作，用於分配一小段字內存單元

1 _software_interrupt:    .word software_interrupt  //_software_interrupt = software_interrupt

12. 下面是reset的代碼

 1 reset:
 2     /*
 3      * set the cpu to SVC32 mode
 4      *//ARM有7種模式，SVC是特權模式，可以訪問所有寄存器
 5     mrs    r0, cpsr
 6     bic    r0, r0, #0x1f
 7     orr    r0, r0, #0xd3
 8     msr    cpsr,r0
33     /* the mask ROM code should have PLL and others stable */
34 #ifndef CONFIG_SKIP_LOWLEVEL_INIT
35     bl    cpu_init_crit
36 #endif

13.首先會將CPU的工作模式設置為svc32模式，然後便調用 cpu_init_crit ，需要註意的是，這裏使用的是 bl 指令，也就是說在運行完 cpu_init_crit 標號處的代碼之後，會通過這個指令返回來

1 mov    pc, lr            @ back to my caller

14. 跳轉到cpu_init_crit

 1 cpu_init_crit:
 2     /*
 3      * Invalidate L1 I/D
 4      */
 5     mov    r0, #0            @ set up for MCR
 6     mcr    p15, 0, r0, c8, c7, 0    @ invalidate TLBs
 7     mcr    p15, 0, r0, c7, c5, 0    @ invalidate icache
 8 
 9     /*
10      * disable MMU stuff and caches
11      */
12     mrc    p15, 0, r0, c1, c0, 0
13     bic    r0, r0, #0x00002000    @ clear bits 13 (--V-)
14     bic    r0, r0, #0x00000007    @ clear bits 2:0 (-CAM)
15     orr    r0, r0, #0x00000002    @ set bit 1 (--A-) Align
16     orr    r0, r0, #0x00000800    @ set bit 12 (Z---) BTB
17     mcr    p15, 0, r0, c1, c0, 0
18 
19     /*
20      * Jump to board specific initialization...
21      * The Mask ROM will have already initialized
22      * basic memory. Go here to bump up clock rate and handle
23      * wake up conditions.
24      */
25     mov    ip, lr            @ persevere link reg across call
26     bl    lowlevel_init        @ go setup pll,mux,memory
27     mov    lr, ip            @ restore link
28     mov    pc, lr            @ back to my caller

15.找到lowlevel_init這個函數，E:\arm_a\IMX6_CoreC_CD\Linux 源碼包\uboot源碼\uboot_IMX6_CoreC_1.3.4_for_Linux\board\freescale\mx6q_sabresd\lowlevel_init.S

1 .globl lowlevel_init
2 lowlevel_init:
3     inv_dcache
4     init_l2cc
5     init_aips
6     init_clock
7     mov pc, lr

16. 接下來一個尷尬的問題，不知道程序接下來往哪裏走了！！假設匯編代碼是順序執行的，那麽接下來是relocate

 1 relocate:                @ relocate U-Boot to RAM
 2     adr    r0, _start        @ r0 <- current position of code
 3     ldr    r1, _TEXT_BASE        @ test if we run from flash or RAM
 4     cmp    r0, r1            @ don‘t reloc during debug
 5     beq    stack_setup
 6 
 7     ldr    r2, _armboot_start
 8     ldr    r3, _bss_start
 9     sub    r2, r3, r2        @ r2 <- size of armboot
10     add    r2, r0, r2        @ r2 <- source end address
11 
12 copy_loop:                @ copy 32 bytes at a time
13     ldmia    r0!, {r3 - r10}        @ copy from source address [r0]
14     stmia    r1!, {r3 - r10}        @ copy to   target address [r1]
15     cmp    r0, r2            @ until source end addreee [r2]
16     ble    copy_loop
17 #endif    /* CONFIG_SKIP_RELOCATE_UBOOT */
18 
19     /* Set up the stack */
20 stack_setup:
21     ldr    r0, _TEXT_BASE        @ upper 128 KiB: relocated uboot
22     sub    r0, r0, #CONFIG_SYS_MALLOC_LEN @ malloc area
23     sub    r0, r0, #CONFIG_SYS_GBL_DATA_SIZE @ bdinfo
24 #ifdef CONFIG_USE_IRQ
25     sub    r0, r0, #(CONFIG_STACKSIZE_IRQ + CONFIG_STACKSIZE_FIQ)
26 #endif
27     sub    sp, r0, #12        @ leave 3 words for abort-stack
28     and    sp, sp, #~7        @ 8 byte alinged for (ldr/str)d
29 
30     /* Clear BSS (if any). Is below tx (watch load addr - need space) */
31 clear_bss:
32     ldr    r0, _bss_start        @ find start of bss segment
33     ldr    r1, _bss_end        @ stop here
34     mov    r2, #0x00000000        @ clear value
35 clbss_l:
36     str    r2, [r0]        @ clear BSS location
37     cmp    r0, r1            @ are we at the end yet
38     add    r0, r0, #4        @ increment clear index pointer
39     bne    clbss_l            @ keep clearing till at end
40 
41 #ifdef CONFIG_ARCH_MMU
42     bl board_mmu_init
43 #endif
44     ldr    pc, _start_armboot    @ jump to C code
45 
46 _start_armboot: .word start_armboot

17. 跳入到C語言函數中start_armboot，但是這個函數在哪裏？還好在書中找到了答案。uboot_IMX6_CoreC_1.3.4_for_Linux\lib_arm\board.c

  1 void start_armboot (void)
  2 {
  3     init_fnc_t **init_fnc_ptr;
  4     char *s;
  5 #if defined(CONFIG_VFD) || defined(CONFIG_LCD)
  6     unsigned long addr;
  7 #endif
  8 
  9     /* Pointer is writable since we allocated a register for it */
 10     gd = (gd_t*)(_armboot_start - CONFIG_SYS_MALLOC_LEN - sizeof(gd_t));
 11     /* compiler optimization barrier needed for GCC >= 3.4 */
 12     __asm__ __volatile__("": : :"memory");
 13 
 14     memset ((void*)gd, 0, sizeof (gd_t));
 15     gd->bd = (bd_t*)((char*)gd - sizeof(bd_t));
 16     memset (gd->bd, 0, sizeof (bd_t));
 17 
 18     gd->flags |= GD_FLG_RELOC;
 19 
 20     monitor_flash_len = _bss_start - _armboot_start;
 21 
 22     for (init_fnc_ptr = init_sequence; *init_fnc_ptr; ++init_fnc_ptr) {
 23         if ((*init_fnc_ptr)() != 0) {
 24             hang ();
 25         }
 26     }
 27 
 28     /* armboot_start is defined in the board-specific linker script */
 29     mem_malloc_init (_armboot_start - CONFIG_SYS_MALLOC_LEN);
 30 
 31 #ifndef CONFIG_SYS_NO_FLASH
 32     /* configure available FLASH banks */
 33     display_flash_config (flash_init ());
 34 #endif /* CONFIG_SYS_NO_FLASH */
 35 
 36 #ifdef CONFIG_VFD
 37 #    ifndef PAGE_SIZE
 38 #      define PAGE_SIZE 4096
 39 #    endif
 40     /*
 41      * reserve memory for VFD display (always full pages)
 42      */
 43     /* bss_end is defined in the board-specific linker script */
 44     addr = (_bss_end + (PAGE_SIZE - 1)) & ~(PAGE_SIZE - 1);
 45     vfd_setmem (addr);
 46     gd->fb_base = addr;
 47 #endif /* CONFIG_VFD */
 48 
 49 #ifdef CONFIG_LCD
 50     /* board init may have inited fb_base */
 51     if (!gd->fb_base) {
 52 #        ifndef PAGE_SIZE
 53 #          define PAGE_SIZE 4096
 54 #        endif
 55         /*
 56          * reserve memory for LCD display (always full pages)
 57          */
 58         /* bss_end is defined in the board-specific linker script */
 59         addr = (_bss_end + (PAGE_SIZE - 1)) & ~(PAGE_SIZE - 1);
 60         lcd_setmem (addr);
 61         gd->fb_base = addr;
 62     }
 63 #endif /* CONFIG_LCD */
 64 
 65 #if defined(CONFIG_CMD_NAND)
 66     puts ("NAND:  ");
 67     nand_init();        /* go init the NAND */
 68 #endif
 69 
 70 #if defined(CONFIG_CMD_ONENAND)
 71     onenand_init();
 72 #endif
 73 
 74 #ifdef CONFIG_HAS_DATAFLASH
 75     AT91F_DataflashInit();
 76     dataflash_print_info();
 77 #endif
 78 
 79 #ifdef CONFIG_GENERIC_MMC
 80 #ifndef CONFIG_DIS_BOARD_INFO
 81     puts ("MMC:   ");
 82 #endif
 83     mmc_initialize (gd->bd);
 84 #endif
 85 
 86     /* initialize environment */
 87     env_relocate ();
 88 
 89 #ifdef CONFIG_VFD
 90     /* must do this after the framebuffer is allocated */
 91     drv_vfd_init();
 92 #endif /* CONFIG_VFD */
 93 
 94 #ifdef CONFIG_SERIAL_MULTI
 95     serial_initialize();
 96 #endif
 97 
 98     /* IP Address */
 99     gd->bd->bi_ip_addr = getenv_IPaddr ("ipaddr");
100 
101 #if defined CONFIG_SPLASH_SCREEN && defined CONFIG_VIDEO_MX5
102     setup_splash_image();
103 #endif
104 
105     stdio_init ();    /* get the devices list going. */
106 
107     jumptable_init ();
108 
109 #if defined(CONFIG_API)
110     /* Initialize API */
111     api_init ();
112 #endif
113 
114     console_init_r ();    /* fully init console as a device */
115 
116 #if defined(CONFIG_ARCH_MISC_INIT)
117     /* miscellaneous arch dependent initialisations */
118     arch_misc_init ();
119 #endif
120 #if defined(CONFIG_MISC_INIT_R)
121     /* miscellaneous platform dependent initialisations */
122     misc_init_r ();
123 #endif
124 
125     /* enable exceptions */
126     enable_interrupts ();
127 
128     /* Perform network card initialisation if necessary */
129 #ifdef CONFIG_DRIVER_TI_EMAC
130     /* XXX: this needs to be moved to board init */
131 extern void davinci_eth_set_mac_addr (const u_int8_t *addr);
132     if (getenv ("ethaddr")) {
133         uchar enetaddr[6];
134         eth_getenv_enetaddr("ethaddr", enetaddr);
135         davinci_eth_set_mac_addr(enetaddr);
136     }
137 #endif
138 
139 #ifdef CONFIG_DRIVER_CS8900
140     /* XXX: this needs to be moved to board init */
141     cs8900_get_enetaddr ();
142 #endif
143 
144 #if defined(CONFIG_DRIVER_SMC91111) || defined (CONFIG_DRIVER_LAN91C96)
145     /* XXX: this needs to be moved to board init */
146     if (getenv ("ethaddr")) {
147         uchar enetaddr[6];
148         eth_getenv_enetaddr("ethaddr", enetaddr);
149         smc_set_mac_addr(enetaddr);
150     }
151 #endif /* CONFIG_DRIVER_SMC91111 || CONFIG_DRIVER_LAN91C96 */
152 
153 #if defined(CONFIG_ENC28J60_ETH) && !defined(CONFIG_ETHADDR)
154     extern void enc_set_mac_addr (void);
155     enc_set_mac_addr ();
156 #endif /* CONFIG_ENC28J60_ETH && !CONFIG_ETHADDR*/
157 
158     /* Initialize from environment */
159     if ((s = getenv ("loadaddr")) != NULL) {
160         load_addr = simple_strtoul (s, NULL, 16);
161     }
162 #if defined(CONFIG_CMD_NET)
163     if ((s = getenv ("bootfile")) != NULL) {
164         copy_filename (BootFile, s, sizeof (BootFile));
165     }
166 #endif
167 
168 #ifdef BOARD_LATE_INIT
169     board_late_init ();
170 #endif
171 
172 #ifdef CONFIG_ANDROID_RECOVERY
173     check_recovery_mode();
174 #endif
175 
176 #if defined(CONFIG_CMD_NET)
177 #if defined(CONFIG_NET_MULTI)
178 #ifndef CONFIG_DIS_BOARD_INFO
179     puts ("Net:   ");
180 #endif
181 #endif
182     eth_initialize(gd->bd);
183 #if defined(CONFIG_RESET_PHY_R)
184     debug ("Reset Ethernet PHY\n");
185     reset_phy();
186 #endif
187 #endif
188 #ifdef CONFIG_FASTBOOT
189     check_fastboot_mode();
190 #endif
191     /* main_loop() can return to retry autoboot, if so just run it again. */
192     for (;;) {
193         main_loop ();
194     }
195 
196     /* NOTREACHED - no way out of command loop except booting */
197 }                            
//結束

天嵌IMX6開發板測試-第一篇