u-boot启动方式：
1.设置CPU为管理者模式
start_code:
/*
* set the cpu to SVC32 mode
*/
mrs r0, cpsr
bic r0, r0, #0x1f
orr r0, r0, #0xd3
msr cpsr, r02.关看门狗，关中断, 设置时钟频率
0x53000000
# define INTMSK 0x4A000008 /* Interrupt-Controller base addresses */
# define INTSUBMSK 0x4A00001C
# define CLKDIVN 0x4C000014 /* clock divisor register */
# endif
ldr r0, =pWTCON
mov r1, #0x0
str r1, [r0]
/*
* mask all IRQs by setting all bits in the INTMR - default
*/
mov r1, #0xffffffff
ldr r0, =INTMSK
str r1, [r0]
# if defined(CONFIG_S3C2410)
ldr r1, =0x3ff
ldr r0, =INTSUBMSK
str r1, [r0]
# endif
/* FCLK:HCLK:PCLK = 1:2:4 */
/* default FCLK is 120 MHz ! */
ldr r0, =CLKDIVN
mov r1, #3
str r1, [r0]
#endif /* CONFIG_S3C24X0 */3.关MMU,初始各个bank
#ifndef CONFIG_SKIP_LOWLEVEL_INIT
bl cpu_init_crit
cpu_init_crit:
/*
* flush v4 I/D caches
*/
mov r0, #0
mcr p15, 0, r0, c7, c7, 0 /* flush v3/v4 cache */
mcr p15, 0, r0, c8, c7, 0 /* flush v4 TLB */
/*
* disable MMU stuff and caches
*/
mrc p15, 0, r0, c1, c0, 0
bic r0, r0, #0x00002300 @ clear bits 13, 9:8 (--V- --RS)
bic r0, r0, #0x00000087 @ clear bits 7, 2:0 (B--- -CAM)
orr r0, r0, #0x00000002 @ set bit 2 (A) Align
orr r0, r0, #0x00001000 @ set bit 12 (I) I-Cache
mcr p15, 0, r0, c1, c0, 0
/*
* before relocating, we have to setup RAM timing
* because memory timing is board-dependend, you will
* find a lowlevel_init.S in your board directory.
*/
mov ip, lr
bl lowlevel_init
mov lr, ip
mov pc, lr
#endif /* CONFIG_SKIP_LOWLEVEL_INIT */lowlevel_init:
/* memory control configuration */
/* make r0 relative the current location so that it */
/* reads SMRDATA out of FLASH rather than memory ! */
ldr r0, =SMRDATA
ldr r1, _TEXT_BASE
sub r0, r0, r1
ldr r1, =BWSCON /* Bus Width Status Controller */
add r2, r0, #13*4
0:
ldr r3, [r0], #4
str r3, [r1], #4
cmp r2, r0
bne 0b
/* everything is fine now */
mov pc, lr
.ltorg
/* the literal pools origin */
SMRDATA:
.word (0+(B1_BWSCON<<4)+(B2_BWSCON<<8)+(B3_BWSCON<<12)+(B4_BWSCON<<16)+(B5_BWSCON<<20)+(B6_BWSCON<<24)+(B7_BWSCON<<28))
.word ((B0_Tacs<<13)+(B0_Tcos<<11)+(B0_Tacc<<8)+(B0_Tcoh<<6)+(B0_Tah<<4)+(B0_Tacp<<2)+(B0_PMC))
.word ((B1_Tacs<<13)+(B1_Tcos<<11)+(B1_Tacc<<8)+(B1_Tcoh<<6)+(B1_Tah<<4)+(B1_Tacp<<2)+(B1_PMC))
.word ((B2_Tacs<<13)+(B2_Tcos<<11)+(B2_Tacc<<8)+(B2_Tcoh<<6)+(B2_Tah<<4)+(B2_Tacp<<2)+(B2_PMC))
.word ((B3_Tacs<<13)+(B3_Tcos<<11)+(B3_Tacc<<8)+(B3_Tcoh<<6)+(B3_Tah<<4)+(B3_Tacp<<2)+(B3_PMC))
.word ((B4_Tacs<<13)+(B4_Tcos<<11)+(B4_Tacc<<8)+(B4_Tcoh<<6)+(B4_Tah<<4)+(B4_Tacp<<2)+(B4_PMC))
.word ((B5_Tacs<<13)+(B5_Tcos<<11)+(B5_Tacc<<8)+(B5_Tcoh<<6)+(B5_Tah<<4)+(B5_Tacp<<2)+(B5_PMC))
.word ((B6_MT<<15)+(B6_Trcd<<2)+(B6_SCAN))
.word ((B7_MT<<15)+(B7_Trcd<<2)+(B7_SCAN))
.word ((REFEN<<23)+(TREFMD<<22)+(Trp<<20)+(Trc<<18)+(Tchr<<16)+REFCNT)
.word 0x32
.word 0x30
.word 0x30 4.进入board_init_f()函数 (初始化定时器,GPIO,串口等,划分内存区域: 清空gd指向的结构体、通过init_sequence函数数组,来初始化各个函数以及逐步填充gd结构体，最后划分内存区域,将数据保存在gd里,然后调用relocate_code()对uboot重定位,gd是用来传递给内核的参数)
call_board_init_f: ldr sp, =(CONFIG_SYS_INIT_SP_ADDR) //CONFIG_SYS_INIT_SP_ADDR=0x30000f80 bic sp, sp, #7 //sp=0x30000f80 ldr r0,=0x00000000 bl board_init_f
反汇编：arm-linux-objdump -D u-boot>u-boot.dis
00000098 <call_board_init_f>: 98: e59fd3d8 ldr sp, [pc, #984] ; 478 <fiq+0x58>
.......
478: 30000f80 .word 0x30000f80
void board_init_f(ulong bootflag){ bd_t *bd; init_fnc_t **init_fnc_ptr; gd_t *id; ulong addr, addr_sp;#ifdef CONFIG_PRAM ulong reg;#endif bootstage_mark_name(BOOTSTAGE_ID_START_UBOOT_F, "board_init_f"); /* Pointer is writable since we allocated a register for it */ gd = (gd_t *) ((CONFIG_SYS_INIT_SP_ADDR) & ~0x07); /* compiler optimization barrier needed for GCC >= 3.4 */ __asm__ __volatile__("": : :"memory"); memset((void *)gd, 0, sizeof(gd_t)); gd->mon_len = _bss_end_ofs;#ifdef CONFIG_OF_EMBED /* Get a pointer to the FDT */ gd->fdt_blob = _binary_dt_dtb_start;#elif defined CONFIG_OF_SEPARATE /* FDT is at end of image */ gd->fdt_blob = (void *)(_end_ofs + _TEXT_BASE);#endif /* Allow the early environment to override the fdt address */ gd->fdt_blob = (void *)getenv_ulong("fdtcontroladdr", 16, (uintptr_t)gd->fdt_blob); for (init_fnc_ptr = init_sequence; *init_fnc_ptr; ++init_fnc_ptr) { if ((*init_fnc_ptr)() != 0) { hang (); } }#ifdef CONFIG_OF_CONTROL /* For now, put this check after the console is ready */ if (fdtdec_prepare_fdt()) { panic("** CONFIG_OF_CONTROL defined but no FDT - please see " "doc/README.fdt-control"); }#endif debug("monitor len: %08lX\n", gd->mon_len); /* * Ram is setup, size stored in gd !! */ debug("ramsize: %08lX\n", gd->ram_size);#if defined(CONFIG_SYS_MEM_TOP_HIDE) /* * Subtract specified amount of memory to hide so that it won't * get "touched" at all by U-Boot. By fixing up gd->ram_size * the Linux kernel should now get passed the now "corrected" * memory size and won't touch it either. This should work * for arch/ppc and arch/powerpc. Only Linux board ports in * arch/powerpc with bootwrapper support, that recalculate the * memory size from the SDRAM controller setup will have to * get fixed. */ gd->ram_size -= CONFIG_SYS_MEM_TOP_HIDE;#endif addr = CONFIG_SYS_SDRAM_BASE + gd->ram_size;#ifdef CONFIG_LOGBUFFER#ifndef CONFIG_ALT_LB_ADDR /* reserve kernel log buffer */ addr -= (LOGBUFF_RESERVE); debug("Reserving %dk for kernel logbuffer at %08lx\n", LOGBUFF_LEN, addr);#endif#endif#ifdef CONFIG_PRAM /* * reserve protected RAM */ reg = getenv_ulong("pram", 10, CONFIG_PRAM); addr -= (reg << 10); /* size is in kB */ debug("Reserving %ldk for protected RAM at %08lx\n", reg, addr);#endif /* CONFIG_PRAM */#if !(defined(CONFIG_SYS_ICACHE_OFF) && defined(CONFIG_SYS_DCACHE_OFF)) /* reserve TLB table */ addr -= (4096 * 4); /* round down to next 64 kB limit */ addr &= ~(0x10000 - 1); gd->tlb_addr = addr; debug("TLB table at: %08lx\n", addr);#endif /* round down to next 4 kB limit */ addr &= ~(4096 - 1); debug("Top of RAM usable for U-Boot at: %08lx\n", addr);#ifdef CONFIG_LCD#ifdef CONFIG_FB_ADDR gd->fb_base = CONFIG_FB_ADDR;#else /* reserve memory for LCD display (always full pages) */ addr = lcd_setmem(addr); gd->fb_base = addr;#endif /* CONFIG_FB_ADDR */#endif /* CONFIG_LCD */ /* * reserve memory for U-Boot code, data & bss * round down to next 4 kB limit */ addr -= gd->mon_len; addr &= ~(4096 - 1); debug("Reserving %ldk for U-Boot at: %08lx\n", gd->mon_len >> 10, addr);#ifndef CONFIG_SPL_BUILD /* * reserve memory for malloc() arena */ addr_sp = addr - TOTAL_MALLOC_LEN; debug("Reserving %dk for malloc() at: %08lx\n", TOTAL_MALLOC_LEN >> 10, addr_sp); /* * (permanently) allocate a Board Info struct * and a permanent copy of the "global" data */ addr_sp -= sizeof (bd_t); bd = (bd_t *) addr_sp; gd->bd = bd; debug("Reserving %zu Bytes for Board Info at: %08lx\n", sizeof (bd_t), addr_sp);#ifdef CONFIG_MACH_TYPE gd->bd->bi_arch_number = CONFIG_MACH_TYPE; /* board id for Linux */#endif addr_sp -= sizeof (gd_t); id = (gd_t *) addr_sp; debug("Reserving %zu Bytes for Global Data at: %08lx\n", sizeof (gd_t), addr_sp); /* setup stackpointer for exeptions */ gd->irq_sp = addr_sp;#ifdef CONFIG_USE_IRQ addr_sp -= (CONFIG_STACKSIZE_IRQ+CONFIG_STACKSIZE_FIQ); debug("Reserving %zu Bytes for IRQ stack at: %08lx\n", CONFIG_STACKSIZE_IRQ+CONFIG_STACKSIZE_FIQ, addr_sp);#endif /* leave 3 words for abort-stack */ addr_sp -= 12; /* 8-byte alignment for ABI compliance */ addr_sp &= ~0x07;#else addr_sp += 128; /* leave 32 words for abort-stack */ gd->irq_sp = addr_sp;#endif debug("New Stack Pointer is: %08lx\n", addr_sp);#ifdef CONFIG_POST post_bootmode_init(); post_run(NULL, POST_ROM | post_bootmode_get(0));#endif gd->bd->bi_baudrate = gd->baudrate; /* Ram ist board specific, so move it to board code ... */ dram_init_banksize(); display_dram_config(); /* and display it */ gd->relocaddr = addr; gd->start_addr_sp = addr_sp; gd->reloc_off = addr - _TEXT_BASE; debug("relocation Offset is: %08lx\n", gd->reloc_off); memcpy(id, (void *)gd, sizeof(gd_t)); relocate_code(addr_sp, id, addr); /* NOTREACHED - relocate_code() does not return */}
init_fnc_t *init_sequence[] = {#if defined(CONFIG_ARCH_CPU_INIT) arch_cpu_init, /* basic arch cpu dependent setup */#endif#if defined(CONFIG_BOARD_EARLY_INIT_F) board_early_init_f,#endif#ifdef CONFIG_OF_CONTROL fdtdec_check_fdt,#endif timer_init, /* initialize timer */#ifdef CONFIG_FSL_ESDHC get_clocks,#endif env_init, /* initialize environment */ init_baudrate, /* initialze baudrate settings */ serial_init, /* serial communications setup */ console_init_f, /* stage 1 init of console */ display_banner, /* say that we are here */#if defined(CONFIG_DISPLAY_CPUINFO) print_cpuinfo, /* display cpu info (and speed) */#endif#if defined(CONFIG_DISPLAY_BOARDINFO) checkboard, /* display board info */#endif#if defined(CONFIG_HARD_I2C) || defined(CONFIG_SOFT_I2C) init_func_i2c,#endif dram_init, /* configure available RAM banks */ NULL,};
5.重定位 (复制uboot,然后修改SDRAM上的uboot链接地址)
copy_loop: ldmia r0!, {r9-r10} /* copy from source address [r0] */ stmia r1!, {r9-r10} /* copy to target address [r1] */ cmp r0, r2 /* until source end address [r2] */ blo copy_loop#ifndef CONFIG_SPL_BUILD /* * fix .rel.dyn relocations */ ldr r0, _TEXT_BASE /* r0 <- Text base */ sub r9, r6, r0 /* r9 <- relocation offset */ ldr r10, _dynsym_start_ofs /* r10 <- sym table ofs */ add r10, r10, r0 /* r10 <- sym table in FLASH */ ldr r2, _rel_dyn_start_ofs /* r2 <- rel dyn start ofs */ add r2, r2, r0 /* r2 <- rel dyn start in FLASH */ ldr r3, _rel_dyn_end_ofs /* r3 <- rel dyn end ofs */ add r3, r3, r0 /* r3 <- rel dyn end in FLASH */fixloop: ldr r0, [r2] /* r0 <- location to fix up, IN FLASH! */ add r0, r0, r9 /* r0 <- location to fix up in RAM */ ldr r1, [r2, #4] and r7, r1, #0xff cmp r7, #23 /* relative fixup? */ beq fixrel cmp r7, #2 /* absolute fixup? */ beq fixabs /* ignore unknown type of fixup */ b fixnextfixabs: /* absolute fix: set location to (offset) symbol value */ mov r1, r1, LSR #4 /* r1 <- symbol index in .dynsym */ add r1, r10, r1 /* r1 <- address of symbol in table */ ldr r1, [r1, #4] /* r1 <- symbol value */ add r1, r1, r9 /* r1 <- relocated sym addr */ b fixnextfixrel: /* relative fix: increase location by offset */ ldr r1, [r0] add r1, r1, r9fixnext: str r1, [r0] add r2, r2, #8 /* each rel.dyn entry is 8 bytes */ cmp r2, r3 blo fixloop#endif
6.清bss
clear_bss:#ifndef CONFIG_SPL_BUILD ldr r0, _bss_start_ofs ldr r1, _bss_end_ofs mov r4, r6 /* reloc addr */ add r0, r0, r4 add r1, r1, r4 mov r2, #0x00000000 /* clear */clbss_l:str r2, [r0] /* clear loop... */ add r0, r0, #4 cmp r0, r1 bne clbss_l bl coloured_LED_init bl red_led_on#endif
7. 跳转到board_init_r()函数,启动流程结束
ldr r0, _board_init_r_ofs adr r1, _start add lr, r0, r1 add lr, lr, r9 /* setup parameters for board_init_r */ mov r0, r5 /* gd_t */ mov r1, r6 /* dest_addr */ /* jump to it ... */ mov pc, lr_board_init_r_ofs: .word board_init_r - _start
void board_init_r(gd_t *id, ulong dest_addr)
{
//硬件初始化...
.........for (;;) { main_loop(); }.........
}