AM335x uboot spl分析.doc

AM335x uboot spl分析芯片到uboot启动流程ROM SPL uboot.img简介在335x 中ROM code是第一级的bootlader。mpu上电后将会自动执行这里的代码，完成部分初始化和引导第二级的bootlader，第二级的bootlader引导第三级bootader，在ti官方上对于第二级和第三级的bootlader由uboot提供。SPLTo unify all existing implementations for a secondary program loader (SPL) and to allow simply adding of new implementations this generic SPL framework has been created. With this framework almost all source files for a board can be reused. No code duplication or symlinking is necessary anymore.1 Basic ARM initialization2 UART console initialization3 Clocks and DPLL locking (minimal) 4 SDRAM initialization5 Mux (minimal) 6 BootDevice initialization(based on where we are booting from.MMC1/MMC2/Nand/Onenand) 7 Bootloading real u-boot from the BootDevice and passing control to it. uboot spl源代码分析一、makefile分析打开spl文件夹只有一个makefile 可见spl都是复用uboot原先的代码。主要涉及的代码文件为u-boot-2011.09-psp04.06.00.03/arch/arm/cpu/armv7u-boot-2011.09-psp04.06.00.03/arch/arm/libu-boot-2011.09-psp04.06.00.03/drivers LDSCRIPT := $(TOPDIR)/board/$(BOARDDIR)/u-boot-spl.lds这个为链接脚本二、u-boot-spl.ldsSram 0x402F0400Sdram 0x80000000.bss.TEXT （arch/arm/cpu/armv7/start.o）.rodata.data_start 为程序开始_image_copy_end_end三、代码解析_start 为程序开始 （arch/arm/cpu/armv7/start.S）.globl _start 这是在定义u-boot的启动定义入口点，汇编程序的缺省入口是 start标号，用户也可以在连接脚本文件中用ENTRY标志指明其它入口点。.global是GNU ARM汇编的一个伪操作，声明一个符号可被其他文档引用，相当于声明了一个全局变量，.globl和.global相同。该部分为处理器的异常处理向量表。地址范围为0x0000 0000 0x0000 0020,刚好8条指令。为什么是8条指令呢？这里来算一算。首先，一条arm指令为32bit（位），0x0000 0020换算成十进制为25=32B（字节），而32（B） = 4 * 8（B） = 4 * 8 * 8（ bit），所以刚好8条指令（一个字节Byte包含8个位bit）。下面是在汇编程序种经常会遇到的异常向量表。Arm处理器一般包括复位、未定义指令、SWI、预取终止、数据终止、IRQ、FIQ等异常，其中U-Boot中关于异常向量的定义如下：_start: b reset _start 标号表明 oot程序从这里开始执行。b是不带返回的跳转（bl是带返回的跳转），意思是无条件直接跳转到reset标号出执行程序。b是最简单的分支，一旦遇到一个 b 指令，ARM 处理器将立即跳转到给定的地址，从那里继续执行。注意存储在分支指令中的实际的值是相对当前的 R15 的值的一个偏移量；而不是一个绝对地址。它的值由汇编器来计算，它是 24 位有符号数，左移两位后有符号扩展为 32 位，表示的有效偏移为 26 位。 ldr pc, _undefined_instr tion /未定义指令 ldr pc, _software_interrupt /软中断SWI ldr pc, _prefetch_abort /预取终止 ldr pc, _data_abort /数访问终止 ldr pc, _not_used ldr pc, _irq /中断请求IRQ ldr pc, _fiq /快速中断FIQ#ifdef CONFIG_SPL_BUILD/该阶段为spl执行下面代码_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 */#else_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 */#endif/* CONFIG_SPL_BUILD */.word为ARM汇编特有的伪操作符，语法如下：.word , 作用：插入一个32-bit的数据队列。（与armasm中的DCD功能相同）.balignl 16,0xdeadbeef.align伪操作用于表示对齐方式：通过添加填充字节使当前位置满足一定的对齐方式。接下来是对各个段代码的定义略Rest： (arch/arm/cpu/armv7/start.S)blsave_boot_paramssave_boot_params: （arch/arm/cpu/armv7/ti81xx/lowlevel_init.S）#ifdef CONFIG_SPL_BUILDldrr4, =ti81xx_boot_device /ti81xx_boot_device = BOOT_DEVICE_NAND/启动方式ldrr5, r0, #BOOT_DEVICE_OFFSETandr5, r5, #BOOT_DEVICE_MASKstrr5, r4#endifbxlr回到reset：(arch/arm/cpu/armv7/start.S)/设置cpu的工作模式 设置CPU的状态类型为SVC特权模式mrsr0, cpsrbicr0, r0, #0x1forrr0, r0, #0xd3msrcpsr,r0cpu_init_crit: (arch/arm/cpu/armv7/start.S)movr0, #0 set up for MCRmcrp15, 0, r0, c8, c7, 0 invalidate TLBsmcrp15, 0, r0, c7, c5, 0 invalidate icachemcrp15, 0, r0, c7, c5, 6 invalidate BP arraymcr p15, 0, r0, c7, c10, 4 DSBmcr p15, 0, r0, c7, c5, 4 ISB/关闭mmu 缓存mrcp15, 0, r0, c1, c0, 0bicr0, r0, #0x00002000 clear bits 13 (-V-)bicr0, r0, #0x00000007 clear bits 2:0 (-CAM)orrr0, r0, #0x00000002 set bit 1 (-A-) Alignorrr0, r0, #0x00000800 set bit 11 (Z-) BTB#ifdef CONFIG_SYS_ICACHE_OFFbicr0, r0, #0x00001000 clear bit 12 (I) I-cache#elseorrr0, r0, #0x00001000 set bit 12 (I) I-cache#endifmcrp15, 0, r0, c1, c0, 0/调用初始化 函数movip, lr persevere link reg across callbllowlevel_init go setup pll,mux,memorylowlevel_init：（arch/arm/cpu/armv7/ti81xx/lowlevel.S）/* The link register is saved in ip by start.S */mov r6, ip/* check if we are already running from RAM */ldr r2, _lowlevel_init_TEXT_BASE:.wordCONFIG_SYS_TEXT_BASE/* Load address (RAM) */#define CONFIG_SYS_TEXT_BASE0x80800000SDRAM的前8MB作为spl的bss段然后前64bytes做为u-boot.img的头ldr r3, _TEXT_BASEsub r4, r2, r3sub r0, pc, r4/设置堆栈指针/* require dummy instr or subtract pc by 4 instead im doing stack init */ldr sp, SRAM_STACKmark1:ldr r5, _mark1sub r5, r5, r2 /* bytes between mark1 and lowlevel_init */sub r0, r0, r5 /* r0 - _start w.r.t current place of execution */mov r10, #0x0 /* r10 has in_ddr used by s_init() */ands r0, r0, #0xC0000000 /* MSB 2 bits 0 then we are in ocmc or DDR */cmp r0, #0x80000000bne s_init_startmov r10, #0x01b s_init_starts_init_start:（arch/arm/cpu/armv7/ti81xx/lowlevel.S）mov r0, r10 /* passing in_ddr in r0 */bl s_init初始化pll mux memery /* back to arch calling code */mov pc, r6call_board_init_f:（arch/arm/cpu/armv7/start.s)/设置堆栈指针，并调用board_init_f ldrsp, =(CONFIG_SYS_INIT_SP_ADDR)bicsp, sp, #7 /* 8-byte alignment for ABI compliance */ldrr0,=0x00000000blboard_init_fvoid board_init_f(ulong dummy)u-boot-2011.09-psp04.06.00.03/arch/arm/cpu/armv7/omap-common/spl.c调用relocate_code(CONFIG_SPL_STACK, &gdata, CONFIG_SPL_TEXT_BASE);这里使用了 CONFIG_SPL_STACK#define CONFIG_SPL_STACKLOW_LEVEL_SRAM_STACK#define LOW_LEVEL_SRAM_STACK(SRAM0_START + SRAM0_SIZE 4) gdata 为.bss 前一段的空间 描述镜像头#define CONFIG_SPL_TEXT_BASE0x402F0400relocate_code: （arch/arm/cpu/armv7/start.s)重载定位代码jump_2_ram: （arch/arm/cpu/armv7/start.s)跳转到spl的第二阶段board_init_r:(u-boot-2011.09-psp04.06.00.03/arch/arm/cpu/armv7/omap-common/spl.c)初始化时钟： t