u-boot启动的第一阶段
u-boot的第一阶段的任务是完成 部分硬件的设置：
1.设置CPU工作在管理员模式
1 mrs r0,cpsr 2 bic r0,r0,#0x1f 3 orr r0,r0,#0xd3 4 msr cpsr,r0
2.关闭看门狗
1 /* turn off the watchdog */ 2 #if defined(CONFIG_S3C2400) 3 # define pWTCON 0x15300000 4 # define INTMSK 0x14400008 /* Interupt-Controller base addresses */ 5 # define CLKDIVN 0x14800014 /* clock divisor register */ 6 #elif defined(CONFIG_S3C2410) 7 # define pWTCON 0x53000000 8 # define INTMOD 0X4A000004 9 # define INTMSK 0x4A000008 /* Interupt-Controller base addresses */ 10 # define INTSUBMSK 0x4A00001C 11 # define CLKDIVN 0x4C000014 /* clock divisor register */ 12 #endif 13 14 #if defined(CONFIG_S3C2400) || defined(CONFIG_S3C2410) 15 ldr r0, =pWTCON 16 mov r1, #0x0 17 str r1, [r0]
3.禁止所有中断
1 mov r1, #0xffffffff 2 ldr r0, =INTMSK 3 str r1, [r0] 4 # if defined(CONFIG_S3C2410) 5 ldr r1, =0x3ff 6 ldr r0, =INTSUBMSK 7 str r1, [r0] 8 # endif
4.设置时钟
1 #define S3C2440_MPLL_400MHZ ((0x5c<<12)|(0x01<<4)|(0x01)) 2 #define S3C2440_UPLL_48MHZ ((0x38<<12)|(0x02<<4)|(0x02)) 3 #define S3C2440_CLKDIV (0x05) // | (1<<3)) /* FCLK:HCLK:PCLK = 1:4:8, UCLK = UPLL/2 */ 4 5 ldr r1, =CLKDIVN 6 mov r2, #S3C2440_CLKDIV 7 str r2, [r1] 8 9 mrc p15, 0, r1, c1, c0, 0 // read ctrl register 10 orr r1, r1, #0xc0000000 // Asynchronous 11 mcr p15, 0, r1, c1, c0, 0 // write ctrl register 12 13 ldr r0,=LOCKTIME 14 ldr r1,=0xffffff 15 str r1,[r0] 16 // delay 17 mov r0, #0x200 18 1: subs r0, r0, #1 19 bne 1b 20 21 // Configure MPLL 22 ldr r0,=MPLLCON 23 ldr r1,=S3C2440_MPLL_400MHZ 24 str r1,[r0] 25 // delay 26 mov r0, #0x200 27 1: subs r0, r0, #1 28 bne 1b 29 30 //Configure UPLL 31 ldr r0, =UPLLCON 32 ldr r1, =S3C2440_UPLL_48MHZ 33 str r1, [r0] 34 // delay 35 mov r0, #0x200 36 1: subs r0, r0, #1 37 bne 1b
5.使能SDRAM
1 adr r0, _start /* r0 <- current position of code */ 2 ldr r1, _TEXT_BASE /* test if we run from flash or RAM */ 3 cmp r0, r1 /* don't reloc during debug */ 4 blne cpu_init_crit 5 6 7 8 cpu_init_crit: 9 /* 10 * flush v4 I/D caches 11 */ 12 mov r0, #0 13 mcr p15, 0, r0, c7, c7, 0 /* flush v3/v4 cache */ 14 mcr p15, 0, r0, c8, c7, 0 /* flush v4 TLB */ 15 16 /* 17 * disable MMU stuff and caches 18 */ 19 mrc p15, 0, r0, c1, c0, 0 20 bic r0, r0, #0x00002300 @ clear bits 13, 9:8 (--V- --RS) 21 bic r0, r0, #0x00000087 @ clear bits 7, 2:0 (B--- -CAM) 22 orr r0, r0, #0x00000002 @ set bit 2 (A) Align 23 orr r0, r0, #0x00001000 @ set bit 12 (I) I-Cache 24 mcr p15, 0, r0, c1, c0, 0 25 26 /* 27 * before relocating, we have to setup RAM timing 28 * because memory timing is board-dependend, you will 29 * find a lowlevel_init.S in your board directory. 30 */ 31 mov ip, lr 32 bl lowlevel_init 33 mov lr, ip 34 mov pc, lr 35 36 37 38 _TEXT_BASE: 39 .word TEXT_BASE 40 41 .globl lowlevel_init 42 lowlevel_init: 43 /* memory control configuration */ 44 /* make r0 relative the current location so that it */ 45 /* reads SMRDATA out of FLASH rather than memory ! */ 46 ldr r0, =SMRDATA 47 ldr r1, _TEXT_BASE 48 sub r0, r0, r1 49 ldr r1, =BWSCON /* Bus Width Status Controller */ 50 add r2, r0, #13*4 51 0: 52 ldr r3, [r0], #4 53 str r3, [r1], #4 54 cmp r2, r0 55 bne 0b 56 57 /* everything is fine now */ 58 mov pc, lr 59 60 .ltorg 61 /* the literal pools origin */ 62 63 SMRDATA: 64 .word (0+(B1_BWSCON<<4)+(B2_BWSCON<<8)+(B3_BWSCON<<12)+(B4_BWSCON<<16)+(B5_BWSCON<<20)+(B6_BWSCON<<24)+(B7_BWSCON<<28)) 65 .word ((B0_Tacs<<13)+(B0_Tcos<<11)+(B0_Tacc<<8)+(B0_Tcoh<<6)+(B0_Tah<<4)+(B0_Tacp<<2)+(B0_PMC)) 66 .word ((B1_Tacs<<13)+(B1_Tcos<<11)+(B1_Tacc<<8)+(B1_Tcoh<<6)+(B1_Tah<<4)+(B1_Tacp<<2)+(B1_PMC)) 67 .word ((B2_Tacs<<13)+(B2_Tcos<<11)+(B2_Tacc<<8)+(B2_Tcoh<<6)+(B2_Tah<<4)+(B2_Tacp<<2)+(B2_PMC)) 68 .word ((B3_Tacs<<13)+(B3_Tcos<<11)+(B3_Tacc<<8)+(B3_Tcoh<<6)+(B3_Tah<<4)+(B3_Tacp<<2)+(B3_PMC)) 69 .word ((B4_Tacs<<13)+(B4_Tcos<<11)+(B4_Tacc<<8)+(B4_Tcoh<<6)+(B4_Tah<<4)+(B4_Tacp<<2)+(B4_PMC)) 70 .word ((B5_Tacs<<13)+(B5_Tcos<<11)+(B5_Tacc<<8)+(B5_Tcoh<<6)+(B5_Tah<<4)+(B5_Tacp<<2)+(B5_PMC)) 71 .word ((B6_MT<<15)+(B6_Trcd<<2)+(B6_SCAN)) 72 .word ((B7_MT<<15)+(B7_Trcd<<2)+(B7_SCAN)) 73 .word ((REFEN<<23)+(TREFMD<<22)+(Trp<<20)+(Trc<<18)+(Tchr<<16)+REFCNT) 74 .word 0xb1 75 .word 0x30 76 .word 0x30
6.设置栈
1 stack_setup: 2 ldr r0, _TEXT_BASE /* upper 128 KiB: relocated uboot */ 3 sub r0, r0, #CFG_MALLOC_LEN /* malloc area */ 4 sub r0, r0, #CFG_GBL_DATA_SIZE /* bdinfo */ 5 6 #ifdef CONFIG_USE_IRQ 7 sub r0, r0, #(CONFIG_STACKSIZE_IRQ+CONFIG_STACKSIZE_FIQ) 8 #endif 9 sub sp, r0, #12 /* leave 3 words for abort-stack */
7.代码重定位
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 clear_bss 6 7 ldr r2, _armboot_start 8 ldr r3, _bss_start 9 sub r2, r3, r2 /* r2 <- size of armboot */ 10 #if 1 11 bl CopyCode2Ram /* r0: source, r1: dest, r2: size */ 12 #else 13 add r2, r0, r2 /* r2 <- source end address */ 14 15 copy_loop: 16 ldmia r0!, {r3-r10} /* copy from source address [r0] */ 17 stmia r1!, {r3-r10} /* copy to target address [r1] */ 18 cmp r0, r2 /* until source end addreee [r2] */ 19 ble copy_loop
1 int CopyCode2Ram(unsigned long start_addr, unsigned char *buf, int size) 2 { 3 unsigned int *pdwDest; 4 unsigned int *pdwSrc; 5 int i; 6 7 if (bBootFrmNORFlash()) 8 { 9 pdwDest = (unsigned int *)buf; 10 pdwSrc = (unsigned int *)start_addr; 11 /* 从 NOR Flash启动 */ 12 for (i = 0; i < size / 4; i++) 13 { 14 pdwDest[i] = pdwSrc[i]; 15 } 16 return 0; 17 } 18 else 19 { 20 /* 初始化NAND Flash */ 21 nand_init_ll(); 22 /* 从 NAND Flash启动 */ 23 nand_read_ll_lp(buf, start_addr, (size + NAND_BLOCK_MASK_LP)&~(NAND_BLOCK_MASK_LP)); 24 return 0; 25 } 26 }
8.清除BSS段
clear_bss: ldr r0, _bss_start /* find start of bss segment */ ldr r1, _bss_end /* stop here */ mov r2, #0x00000000 /* clear */ clbss_l:str r2, [r0] /* clear loop... */ add r0, r0, #4 cmp r0, r1 ble clbss_l
第一阶段到这结束，后面经过一个C函数跳转至u-boot启动的第二阶段
