本文主要探讨x210的uboot的start.S文件,也是uboot启动的第一阶段。
头文件
config.h
config.h == x210_sd.h,由mkconfig脚本生成,包含了开发板的配置宏
root@kaxi-virtual-machine:~/qt_x210v3s_160307/uboot/include# cat config.h
/* Automatically generated - do not edit */
#include <configs/x210_sd.h>
version.h
#ifndef __VERSION_H__
#define __VERSION_H__#ifndef DO_DEPS_ONLY
#include "version_autogenerated.h"
#endif#endif /* __VERSION_H__ */root@kaxi-virtual-machine:~/qt_x210v3s_160307/uboot/include# cat version_autogenerated.h
#define U_BOOT_VERSION "U-Boot 1.3.4"定义uboot版本号,uboot启动时打印的版本信息
asm/proc/domain.h
asm/proc/domain.h == include/asm-arm/proc-armv/domain.h
regs.h
regs.h == s5pc110.h
16字节头
#if defined(CONFIG_EVT1) && !defined(CONFIG_FUSED).word 0x2000.word 0x0.word 0x0.word 0x0
#endif定义16字节头,用于存放校验信息
异常向量表构建
.globl _start
_start: b resetldr pc, _undefined_instructionldr pc, _software_interruptldr pc, _prefetch_abortldr pc, _data_abortldr pc, _not_usedldr pc, _irqldr pc, _fiq_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 *//** the actual reset code*/reset:/** set the cpu to SVC32 mode and IRQ & FIQ disable*/@;mrs r0,cpsr@;bic r0,r0,#0x1f@;orr r0,r0,#0xd3@;msr cpsr,r0msr cpsr_c, #0xd3 @ I & F disable, Mode: 0x13 - SVC 将CPU设置为禁止FIQ和IRQ,置于ARM状态设置SVC模式
CPU复位默认进入SVC模式,uboot工作于SVC模式
.balignl 16,0xdeadbeef. 对齐访问效率快,是硬件要求
TEXT_BASE
_TEXT_BASE:.word TEXT_BASEroot@kaxi-virtual-machine:~/qt_x210v3s_160307/uboot/board/samsung/x210# cat config.mk
TEXT_BASE = 0xc3e00000x210_nand_config : unconfig@$(MKCONFIG) $(@:_config=) arm s5pc11x x210 samsung s5pc110@echo "TEXT_BASE = 0xc3e00000" > $(obj)board/samsung/x210/config.mk
定义uboot链接地址(0xc3e00000)
make x210_sd_config(调用mkconfig脚本) ==> uboot/board/samsung/x210/config.mk
CFG_PHY_UBOOT_BASE
_TEXT_PHY_BASE:.word CFG_PHY_UBOOT_BASECFG_PHY_UBOOT_BASE为0x33e0000是uboot在DDR中的物理地址
cpu_init_crit(设置L2、L1cache、MMU)
bl disable_l2cache // 禁止L2 cache
bl set_l2cache_auxctrl_cycle // l2 cache相关初始化
bl enable_l2cache // 使能l2 cache
刷新L1 cache、icache、dcache。
关闭MMU
cpu_init_crit:bl disable_l2cachebl set_l2cache_auxctrl_cyclebl enable_l2cache/** Invalidate L1 I/D*/mov r0, #0 @ set up for MCRmcr p15, 0, r0, c8, c7, 0 @ invalidate TLBsmcr p15, 0, r0, c7, c5, 0 @ invalidate icache/** disable MMU stuff and caches*/mrc p15, 0, r0, c1, c0, 0bic r0, r0, #0x00002000 @ clear bits 13 (--V-)bic r0, r0, #0x00000007 @ clear bits 2:0 (-CAM)orr r0, r0, #0x00000002 @ set bit 1 (--A-) Alignorr r0, r0, #0x00000800 @ set bit 12 (Z---) BTBmcr p15, 0, r0, c1, c0, 0启动介质选择
/* Read booting information */ldr r0, =PRO_ID_BASEldr r1, [r0,#OMR_OFFSET]bic r2, r1, #0xffffffc1/* NAND BOOT */cmp r2, #0x0 @ 512B 4-cyclemoveq r3, #BOOT_NANDcmp r2, #0x2 @ 2KB 5-cyclemoveq r3, #BOOT_NANDcmp r2, #0x4 @ 4KB 5-cycle 8-bit ECCmoveq r3, #BOOT_NANDcmp r2, #0x6 @ 4KB 5-cycle 16-bit ECCmoveq r3, #BOOT_NANDcmp r2, #0x8 @ OneNAND Muxmoveq r3, #BOOT_ONENAND/* SD/MMC BOOT */cmp r2, #0xcmoveq r3, #BOOT_MMCSD /* NOR BOOT */cmp r2, #0x14moveq r3, #BOOT_NOR /* Uart BOOTONG failed */cmp r2, #(0x1<<4)moveq r3, #BOOT_SEC_DEVldr r0, =INF_REG_BASEstr r3, [r0, #INF_REG3_OFFSET]寄存器(0xE0000004)存储OM引脚接法,用于判断启动介质是Nand还是SD等
设置栈(SRAM栈)并调用lowlevel_init
/** Go setup Memory and board specific bits prior to relocation.*/ldr sp, =0xd0036000 /* end of sram dedicated to u-boot */sub sp, sp, #12 /* set stack */mov fp, #0bl lowlevel_init /* go setup pll,mux,memory */设置栈(0xd0036000,第一次),当前代码在SRAM运行,DDR未初始化
lowlevel_init.S
uboot/board/samsumg/x210/lowlevel_init.S
push {lr}
由于lowlevel_init.S还调用了其他函数,防止之前的lr被覆盖(bl lowlevel_init处的地址),需先入栈
检查复位状态
/* check reset status */ldr r0, =(ELFIN_CLOCK_POWER_BASE+RST_STAT_OFFSET)ldr r1, [r0]bic r1, r1, #0xfff6ffffcmp r1, #0x10000beq wakeup_reset_precmp r1, #0x80000beq wakeup_reset_from_didle CPU允许复位情况：冷上电、热启动、睡眠唤醒等
依据复位状态初始化DDR：冷上电DDR需初始化,热启动或低功耗不需要
IO状态恢复
/* IO Retention release */ldr r0, =(ELFIN_CLOCK_POWER_BASE + OTHERS_OFFSET)ldr r1, [r0]ldr r2, =IO_RET_RELorr r1, r1, r2str r1, [r0]关看门狗
/* Disable Watchdog */ldr r0, =ELFIN_WATCHDOG_BASE /* 0xE2700000 */mov r1, #0str r1, [r0]SRAM,SROM的GPIO设置
/* SRAM(2MB) init for SMDKC110 *//* GPJ1 SROM_ADDR_16to21 */ldr r0, =ELFIN_GPIO_BASEldr r1, [r0, #GPJ1CON_OFFSET]bic r1, r1, #0xFFFFFFldr r2, =0x444444orr r1, r1, r2str r1, [r0, #GPJ1CON_OFFSET]ldr r1, [r0, #GPJ1PUD_OFFSET]ldr r2, =0x3ffbic r1, r1, r2str r1, [r0, #GPJ1PUD_OFFSET]/* GPJ4 SROM_ADDR_16to21 */ldr r1, [r0, #GPJ4CON_OFFSET]bic r1, r1, #(0xf<<16)ldr r2, =(0x4<<16)orr r1, r1, r2str r1, [r0, #GPJ4CON_OFFSET]ldr r1, [r0, #GPJ4PUD_OFFSET]ldr r2, =(0x3<<8)bic r1, r1, r2str r1, [r0, #GPJ4PUD_OFFSET]/* CS0 - 16bit sram, enable nBE, Byte base address */ldr r0, =ELFIN_SROM_BASE /* 0xE8000000 */mov r1, #0x1str r1, [r0]供电锁存
/* PS_HOLD pin(GPH0_0) set to high */ldr r0, =(ELFIN_CLOCK_POWER_BASE + PS_HOLD_CONTROL_OFFSET)ldr r1, [r0]orr r1, r1, #0x300 orr r1, r1, #0x1 str r1, [r0]判断执行代码位置
/* when we already run in ram, we don't need to relocate U-Boot.* and actually, memory controller must be configured before U-Boot* is running in ram.*/ldr r0, =0xff000fffbic r1, pc, r0 /* r0 <- current base addr of code */ldr r2, _TEXT_BASE /* r1 <- original base addr in ram */bic r2, r2, r0 /* r0 <- current base addr of code */cmp r1, r2 /* compare r0, r1 */beq 1f /* r0 == r1 then skip sdram init */对比运行地址和链接地址来判断在SRAM中（不相等）还是DDR中（相等）,从而决定是否要时钟和DDR初始化
system_clock_init,x210_sd.h有时钟相关配置值
mem_ctrl_asm_init(uboot/cpu/s5pc11x/s5pc110/cpu_init.S)初始化DDR
uboot中DMC0的256MB内存地址范围为0x30000000-0x3FFFFFFF
uboot物理地址范围为：0x30000000-0x4FFFFFFF共512MB,30000000-3FFFFFFF为DMC0,40000000-4FFFFFFF为DMC1
uart_asm_init初始化串口,发送'O',
tzpc_init,trust zone初始化
通过串口打印'K'
设置栈（33E00000,DDR栈,二次）和重定位
/* get ready to call C functions */ldr sp, _TEXT_PHY_BASE /* setup temp stack pointer */sub sp, sp, #12mov fp, #0 /* no previous frame, so fp=0 *//* when we already run in ram, we don't need to relocate U-Boot.* and actually, memory controller must be configured before U-Boot* is running in ram.*/ldr r0, =0xff000fffbic r1, pc, r0 /* r0 <- current base addr of code */ldr r2, _TEXT_BASE /* r1 <- original base addr in ram */bic r2, r2, r0 /* r0 <- current base addr of code */cmp r1, r2 /* compare r0, r1 */beq after_copy /* r0 == r1 then skip flash copy */#if defined(CONFIG_EVT1)/* If BL1 was copied from SD/MMC CH2 */ldr r0, =0xD0037488ldr r1, [r0]ldr r2, =0xEB200000cmp r1, r2beq mmcsd_boot
#endifldr r0, =INF_REG_BASEldr r1, [r0, #INF_REG3_OFFSET]cmp r1, #BOOT_NAND /* 0x0 => boot device is nand */beq nand_bootcmp r1, #BOOT_ONENAND /* 0x1 => boot device is onenand */beq onenand_bootcmp r1, #BOOT_MMCSDbeq mmcsd_bootcmp r1, #BOOT_NORbeq nor_bootcmp r1, #BOOT_SEC_DEVbeq mmcsd_bootnand_boot:mov r0, #0x1000bl copy_from_nandb after_copyonenand_boot:bl onenand_bl2_copyb after_copymmcsd_boot:
#if DELETEldr sp, _TEXT_PHY_BASE sub sp, sp, #12mov fp, #0
#endifbl movi_bl2_copyb after_copynor_boot:bl read_hwordb after_copy 冷启动uboot的16kb从SD卡加载到SRAM中运行,要加载第二部分(SD卡)到DDR中(33e00000)
D0037488内存地址(SRAM)是硬件设置,根据SD启动的通道修改值,EB000000为SD1启动,EB200000为SD2启动
start.S的260确定MMCSD启动,278将BOOT_MMCSD写入INF_REG3寄存器,322读去并和和BOOT_MMCSD对比确定从MMCSD启动,跳转到mmcsd_boot
uboot/cpu/s5pc11x/movi.c中调用movi_bl2_copy函数完成重定位
copy_bl2(2, MOVI_BL2_POS, MOVI_BL2_BLKCNT,CFG_PHY_UBOOT_BASE, 0); 2表示通道2
MOVI_BL2_POS第二部分在SD卡中的开始扇区,和烧录uboot烧录位置相同
MOVI_BL2_BLKCNT是uboot长度占用的扇区数
CFG_PHY_UBOOT_BASE是重定位将第二部分复制到DDR中的起始地址(33E00000)
虚拟地址映射
after_copy:#if defined(CONFIG_ENABLE_MMU)
enable_mmu:/* enable domain access */ldr r5, =0x0000ffffmcr p15, 0, r5, c3, c0, 0 @load domain access register/* Set the TTB register */ldr r0, _mmu_table_baseldr r1, =CFG_PHY_UBOOT_BASEldr r2, =0xfff00000bic r0, r0, r2orr r1, r0, r1mcr p15, 0, r1, c2, c0, 0/* Enable the MMU */
mmu_on:mrc p15, 0, r0, c1, c0, 0orr r0, r0, #1mcr p15, 0, r0, c1, c0, 0nopnopnopnop
#endif MMU实现虚拟地址到物理地址映射,在CP15协处理器中进行控制
cp15的c3寄存器是使能域访问,及控制访问权限
cp15的c2寄存器是设置TTB(转换表基地址)
转换表是虚拟地址映射的关键包含表索引和表项,表索引对应虚拟地址,表项对应物理地址,表索引和表项构成转换表单元,可对内存块进行虚拟地址转换(ARM中包含3种块大小：细表1KB、粗表4KB、段1MB),转换表由转换表单元构成,每个单元对应1个内存块,整体对应整个内存空间(0-4G)的映射
转换表在内存中,将基地址TTB设置到cp15的c2寄存器中,MMU工作时自动调用
cp15的c1寄存器使能MMU单元
再次设置栈(三次,DDR)
skip_hw_init:/* Set up the stack */
stack_setup:
#if defined(CONFIG_MEMORY_UPPER_CODE)ldr sp, =(CFG_UBOOT_BASE + CFG_UBOOT_SIZE - 0x1000)
#elseldr r0, _TEXT_BASE /* upper 128 KiB: relocated uboot */sub r0, r0, #CFG_MALLOC_LEN /* malloc area */sub r0, r0, #CFG_GBL_DATA_SIZE /* bdinfo */
#if defined(CONFIG_USE_IRQ)sub r0, r0, #(CONFIG_STACKSIZE_IRQ+CONFIG_STACKSIZE_FIQ)
#endifsub sp, r0, #12 /* leave 3 words for abort-stack */#endif栈设置在uboot起始地址上方2MB处,安全栈空间是：2MB减去uboot大小
清理bss
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, #4cmp r0, r1ble clbss_l执行二阶段代码
ldr pc, _start_armboot_start_armboot:.word start_armboot#if defined(CONFIG_ENABLE_MMU)
_mmu_table_base:.word mmu_table
#endifstart_armboot在uboot/lib_arm/board.c
uboot一阶段
构建异常向量表,启动介质选择,设置CPU为SVC模式,关看门狗,开发板供电置锁,时钟初始化,DDR初始化,串口初始化并打印"OK",重定位,建立映射表并开启MMU,清理bss,跳转到第二阶段
