韦东山老师教学视频

0.环境搭建过程中遇到的问题

1.解决THE FOLLOWING PACKAGES HAVE UNMET DEPENDENCIES问题！！！

终于搭建完成开发环境： 2.执行编译指令报错 Ubuntu下手动安装clang：

apt-get install clang

进入《Configuring_ubuntu.sh》文件搜索clang，发现如下代码，这是该脚本不支持ubuntu16的意思么？ 似乎是… 经过实测需要使用ubuntu18.04

1.启动流程分析

reset_vector_up.s 1.关中断；设置CPU为SVC32模式；

/* * disable interrupts (FIQ and IRQ), also set the cpu to SVC32 mode, * except if in HYP mode already */ mrs r0, cpsr and r1, r0, #0x1f @ mask mode bits teq r1, #0x1a @ test for HYP mode bicne r0, r0, #0x1f @ clear all mode bits orrne r0, r0, #0x13 @ set SVC mode orr r0, r0, #0xc0 @ disable FIQ and IRQ msr cpsr,r0

2.禁止I-cache；

/* * If I-cache is enabled invalidate it */ mcr p15, 0, r0, c7, c5, 0 @ invalidate icache mcr p15, 0, r0, c7, c10, 4 @ DSB mcr p15, 0, r0, c7, c5, 4 @ ISB

3.重定位（把程序复制到运行地址）；

/* r11: delta of physical address and virtual address */ adr r11, pa_va_offset //把变量pa_va_offset的地址给r11 ldr r0, [r11] //把变量r11存储的变量作为地址，指向的数据给r0 sub r11, r11, r0 //计算地址偏差 /* if we need to relocate to proper location or not */ adr r4, __exception_handlers /* r4: base of load address */ /*__exception_handlers就是异常向量表的首地址，也就是整个程序运行的首地址*/ ldr r5, =SYS_MEM_BASE /* r5: base of physical address*/ /* 处理器内部DDR的物理空间起始地址 */ subs r12, r4, r5 /* r12: delta of load address and physical address */ beq reloc_img_to_bottom_done /* if we load image at the bottom of physical address */ /* 若当前的运行地址和物理地址一致，则跳转到下面的函数，无需进行进行搬运 ，即重定位*/

3.1.搬运分支

/* we need to relocate image at the bottom of physical address */ ldr r7, =__exception_handlers /* r7: base of linked address (or vm address) */ /* r7=实际程序代码段的首地址 */ ldr r6, =__bss_start /* r6: end of linked address (or vm address) */ /* r6=实际程序代码段的末地址 */ sub r6, r7 /* r6: delta of linked address (or vm address) */ /* r6=实际程序代码段的长度 */ add r6, r4 /* r6: end of load address */ /* r6=实际程序代码段的末地址 */ /* 循环搬运 */ reloc_img_to_bottom_loop: ldr r7, [r4], #4 str r7, [r5], #4 cmp r4, r6 bne reloc_img_to_bottom_loop sub pc, r12 nop sub r11, r11, r12 /* r11: eventual address offset */

3.2.无需搬运分支

ldr r4, =g_firstPageTable /* r4: physical address of translation table and clear it */ /* r4=页表的物理地址起始地址 */ add r4, r4, r11 bl page_table_clear /* 页表空间清零 */

4.LINE175：设置页表（虚拟地址转换为物理地址），代码如下

PAGE_TABLE_SET SYS_MEM_BASE, UNCACHED_VMM_BASE, UNCACHED_VMM_SIZE, MMU_INITIAL_MAP_STRONGLY_ORDERED #ifdef LOSCFG_PLATFORM_IMX6ULL PAGE_TABLE_SET DDR_RAMFS_ADDR, DDR_RAMFS_VBASE, DDR_RAMFS_SIZE, MMU_INITIAL_MAP_DEVICE PAGE_TABLE_SET LCD_FB_BASE, LCD_FB_VBASE, LCD_FB_SIZE, MMU_INITIAL_MAP_DEVICE #endif PAGE_TABLE_SET SYS_MEM_BASE, KERNEL_VMM_BASE, KERNEL_VMM_SIZE, MMU_DESCRIPTOR_KERNEL_L1_PTE_FLAGS PAGE_TABLE_SET PERIPH_PMM_BASE, PERIPH_DEVICE_BASE, PERIPH_DEVICE_SIZE, MMU_INITIAL_MAP_DEVICE PAGE_TABLE_SET PERIPH_PMM_BASE, PERIPH_CACHED_BASE, PERIPH_CACHED_SIZE, MMU_DESCRIPTOR_KERNEL_L1_PTE_FLAGS PAGE_TABLE_SET PERIPH_PMM_BASE, PERIPH_UNCACHED_BASE, PERIPH_UNCACHED_SIZE, MMU_INITIAL_MAP_STRONGLY_ORDERED

其中，PAGE_TABLE_SET 为宏定义，其定义在reset_vector_up.s为：

/* param0 is physical address, 物理地址 param1 virtual address, 虚拟地址 param2 is sizes, 大小 param3 is flag 标志 */ .macro PAGE_TABLE_SET param0, param1, param2, param3 ldr r6, =\param0 ldr r7, =\param1 ldr r8, =\param2 ldr r10, =\param3 bl page_table_build .endm

在MMU启动之前，CPU发出的地址可以直接到达设备，之后则需要经过MMU再发给设备（关于页表和MMU的具体值是参见《嵌入式Linux应用开发完全手册_韦东山全系列视频文档全集V2.4》P639）

bl mmu_setup /* set up the mmu */

5.多核心CPU的处理方式

/* get cpuid and keep it in r11 */ mrc p15, 0, r11, c0, c0, 5 and r11, r11, #MPIDR_CPUID_MASK /* 判断当前的core是否为核0，若为核0则初始化堆栈，若不是则跳过 */ cmp r11, #0 bne excstatck_loop_done excstatck_loop: /* clear out the interrupt and exception stack and set magic num to check the overflow */ ldr r0, =__undef_stack ldr r1, =__exc_stack_top bl stack_init STACK_MAGIC_SET __undef_stack, #OS_EXC_UNDEF_STACK_SIZE, OS_STACK_MAGIC_WORD STACK_MAGIC_SET __abt_stack, #OS_EXC_ABT_STACK_SIZE, OS_STACK_MAGIC_WORD STACK_MAGIC_SET __irq_stack, #OS_EXC_IRQ_STACK_SIZE, OS_STACK_MAGIC_WORD STACK_MAGIC_SET __fiq_stack, #OS_EXC_FIQ_STACK_SIZE, OS_STACK_MAGIC_WORD STACK_MAGIC_SET __svc_stack, #OS_EXC_SVC_STACK_SIZE, OS_STACK_MAGIC_WORD STACK_MAGIC_SET __exc_stack, #OS_EXC_STACK_SIZE, OS_STACK_MAGIC_WORD excstatck_loop_done:

6.设置堆栈

/* set svc stack, every cpu has OS_EXC_SVC_STACK_SIZE stack */ ldr r0, =__svc_stack_top mov r2, #OS_EXC_SVC_STACK_SIZE mul r2, r2, r11 sub r0, r0, r2 mov sp, r0

7.设置FPU+NEON

/* enable fpu+neon */ MRC p15, 0, r0, c1, c1, 2 ORR r0, r0, #0xC00 BIC r0, r0, #0xC000 MCR p15, 0, r0, c1, c1, 2 LDR r0, =(0xF << 20) MCR p15, 0, r0, c1, c0, 2 MOV r3, #0x40000000 VMSR FPEXC, r3 LDR r0, =__exception_handlers MCR p15, 0, r0, c12, c0, 0 cmp r11, #0 bne cpu_start

8.跳转到main函数

bl main

9.跳转到main函数-路径\kernel\liteos_a\platform

LITE_OS_SEC_TEXT_INIT INT32 main(VOID) { UINT32 uwRet = LOS_OK; OsSetMainTask(); OsCurrTaskSet(OsGetMainTask()); /* set smp system counter freq */ #if (LOSCFG_KERNEL_SMP == YES) #ifndef LOSCFG_TEE_ENABLE HalClockFreqWrite(OS_SYS_CLOCK); #endif #endif /* system and chip info */ OsSystemInfo(); PRINT_RELEASE("\nmain core booting up...\n"); uwRet = OsMain(); if (uwRet != LOS_OK) { return LOS_NOK; } #if (LOSCFG_KERNEL_SMP == YES) PRINT_RELEASE("releasing %u secondary cores\n", LOSCFG_KERNEL_SMP_CORE_NUM - 1); release_secondary_cores(); #endif CPU_MAP_SET(0, OsHwIDGet()); OsStart(); while (1) { __asm volatile("wfi"); } }

7.跳转到uwRet = OsMain();函数 （1）串口初始化；uart_init(); （2）操作系统任务初始化；ret = OsTaskInit(); （3）操作系统内存初始化；ret = OsSysMemInit(); …