Yamon startup分析（未整理四）

                                         作者：makethyme

接上...，继续分析arch/reset/init.S

finish_initialisation:DISP_STR(msg_platform)/* perform platform specific initialisaton. this does not include memory test/clearthe function returns the following parameters:v0 = error code (0 = no error) 返回值中v0表示error code, v1表示RAM长度v1 = RAM size in bytes*/jal sys_init_platform 看下面的分析nop1：bne v0, zero, errornopmove s0, v1 将RAM size放入s0/* s0 holde RAM size, now perform memory test/clear */DISP_STR(msq_ram)move a0, s0jal sys_memory_setup memory setup包括memory test和bss section initializationbne v0, zero, error nop/* COPY code to RAM */DISP_STR(msg_copy_code)#ifndef _SIMULATE_la a0, _etext_init /*SRC*/ 其中_etext_init, _ftext_ram, _etext_ram都是定义在link_el.xn中根据网上文章对linker script的分析，text_init不需要拷贝到RAM中；text_init包含了reset目录下文件的代码。而其结尾就是_etext_init.接下来定义text_ram，并提到AT(_etext_init)表示设置LMA,这样binary格式中text_ram段就仅跟着text_init段，但是这个段不能直接运行，要搬到它的VMA(0x80005000)处才能运行，如果不设置LMA，那默认LMA=VMA，它和上一段就不是紧挨着的，这样最后产生的binary格式文件会很大。另外，bss段和sbss段在映像文件中不占用空间的，但是并不阻止连接器定位符的移动，_end-_fbss就等于实际空间大小，要手动在RAM中分配。la a1, _ftext_ram /* DST*/la a2, _etext_ram /*STOP*/bal copy_textnop/* copy the wait code to memory so that it is not running from flash */la a0, waitcode_start /*SRC*/ 将本来分配在text_init中的代码waitcode_start拷贝到RAM中li a1, SCRLAUNCH ／＊DST＊／li a2, SCRLAUNCH + （waitcode_end – waitcode_start） /* stop */bal copy_text 接上..., 将数据/代码拷贝到RAM中。

copy_data: 将初始化数据拷贝到RAM中DISP_STR(msg_copy_data)la t0, _etext /*SRC*/ 在linker script中是LMA地址la t1, _fdata /* DST*/ 在linker script中就是VMA地址la t2, _fbss /*STOP*/KSEG0A(t1)KSEG0A(t2) beq t1,t2, setup_sp nop addiu t2, -41 : lw t3, 0(t0) add t0, 4 sw t3, 0(t1) bne t1, t2, 1b add t1, 4#define VERIFY_COPYDATA#ifdef VERIFY_COPYDATA根据是否定义了VERIFY_COPYDATA，如果定义了，则读出这些数值进行比较，确定是否正确。#endif接上面，设置stacksetup_sp:/* setup sp (at top of memory) */DISP_STR(msg_sp)la sp,_ freemen 根据link script，_freemen在bss/sbss段之后了li t0, SYS_STACK_SIZE 定义为0x5000addu sp, t0 设定spli t0, ~0xfand sp, t0 /* align sp to 16 byte boundary *//* store system info */DISP_STR(msg_info)la t0, sys_processorsw k1, 0(t0) k1中保存了processor信息la t0, sys_ramsizesw s0, 0(t0)

 

/* Determine cache info and store it */ 接下来部分，跟cache相关，暂时不讨论/* calc first free RAM address. We add the dcache line size to avoid cache writebackproblem if user executes uncached code */li t0, SYS_APPL_STACK_SIZEaddu t0, spaddu t0, v0la t1, sys_freememsw t0, 0(t1)/* C-functions can now be called (memory ready and sp, gp have been set). Interrupts are disabled. we are using the exception handlers of the bootprom*//* call the first c-function. it should never return. if it does, we consider it an error,and expect vo t0 hold the error code.*/DISP_STR(msg_main)li t0, 4*4 用于参数传递subu sp, t0la t0, c_entryjalr t0noperror :/*Error handling. Display error code(if device for this is available) enter an infinite loop (from init.h) */ERROR_HANDLINGend(_reset_handler) 至此，函数进入到C语言的世界。第一个函数是c_entry.