liteOS-A学习笔记-1.环境搭建过程中遇到的问题+启动流程分析

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, cpsrand	r1, r0, #0x1f		@ mask mode bitsteq	r1, #0x1a		@ test for HYP modebicne	r0, r0, #0x1f		@ clear all mode bitsorrne	r0, r0, #0x13		@ set SVC modeorr	r0, r0, #0xc0		@ disable FIQ and IRQmsr	cpsr,r0

2.禁止I-cache；

	/** If I-cache is enabled invalidate it*/mcr	p15, 0, r0, c7, c5, 0	@ invalidate icachemcr     p15, 0, r0, c7, c10, 4	@ DSBmcr     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], #4str     r7, [r5], #4cmp     r4, r6bne     reloc_img_to_bottom_loopsub     pc, r12nopsub     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, r11bl      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_IMX6ULLPAGE_TABLE_SET DDR_RAMFS_ADDR, DDR_RAMFS_VBASE, DDR_RAMFS_SIZE, MMU_INITIAL_MAP_DEVICEPAGE_TABLE_SET LCD_FB_BASE, LCD_FB_VBASE, LCD_FB_SIZE, MMU_INITIAL_MAP_DEVICE
#endifPAGE_TABLE_SET SYS_MEM_BASE, KERNEL_VMM_BASE, KERNEL_VMM_SIZE, MMU_DESCRIPTOR_KERNEL_L1_PTE_FLAGSPAGE_TABLE_SET PERIPH_PMM_BASE, PERIPH_DEVICE_BASE, PERIPH_DEVICE_SIZE, MMU_INITIAL_MAP_DEVICEPAGE_TABLE_SET PERIPH_PMM_BASE, PERIPH_CACHED_BASE, PERIPH_CACHED_SIZE, MMU_DESCRIPTOR_KERNEL_L1_PTE_FLAGSPAGE_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, param3ldr     r6, =\param0ldr     r7, =\param1ldr     r8, =\param2ldr     r10, =\param3bl      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, 5and     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, #0bne     excstatck_loop_doneexcstatck_loop:/* clear out the interrupt and exception stack and set magic num to check the overflow */ldr     r0, =__undef_stackldr     r1, =__exc_stack_topbl      stack_initSTACK_MAGIC_SET __undef_stack, #OS_EXC_UNDEF_STACK_SIZE, OS_STACK_MAGIC_WORDSTACK_MAGIC_SET __abt_stack, #OS_EXC_ABT_STACK_SIZE, OS_STACK_MAGIC_WORDSTACK_MAGIC_SET __irq_stack, #OS_EXC_IRQ_STACK_SIZE, OS_STACK_MAGIC_WORDSTACK_MAGIC_SET __fiq_stack, #OS_EXC_FIQ_STACK_SIZE, OS_STACK_MAGIC_WORDSTACK_MAGIC_SET __svc_stack, #OS_EXC_SVC_STACK_SIZE, OS_STACK_MAGIC_WORDSTACK_MAGIC_SET __exc_stack, #OS_EXC_STACK_SIZE, OS_STACK_MAGIC_WORDexcstatck_loop_done:

6.设置堆栈

    /* set svc stack, every cpu has OS_EXC_SVC_STACK_SIZE stack */ldr    r0, =__svc_stack_topmov    r2, #OS_EXC_SVC_STACK_SIZEmul    r2, r2, r11sub    r0, r0, r2mov    sp, r0

7.设置FPU+NEON

    /* enable fpu+neon */MRC    p15, 0, r0, c1, c1, 2ORR    r0, r0, #0xC00BIC    r0, r0, #0xC000MCR    p15, 0, r0, c1, c1, 2LDR    r0, =(0xF << 20)MCR    p15, 0, r0, c1, c0, 2MOV    r3, #0x40000000VMSR   FPEXC, r3LDR    r0, =__exception_handlersMCR    p15, 0, r0, c12, c0, 0cmp    r11, #0bne    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_ENABLEHalClockFreqWrite(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();
#endifCPU_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();
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