关于裸机程序的启动代码startup.s

一直搞不懂这个裸机程序的启动代码应该怎么写，有些很简单，有些又很复杂。

    IMPORT      _main                    ; C entrypoint for Steppingstone loader.
    AREA |C$$code|, CODE, READONLY
    global        Start

Start
        b        _main

        DCB        "ABCDabcd"
        END

像这个就很简单
;*************************************************************************************/

                GET        option.inc

;=======================================================
;                        ENTRY  
;=======================================================

                AREA    Init,CODE,READONLY

                ENTRY
ResetHandler
                
                LDR R13, =top_of_stacks

    [ (USE_TCM = 1)
; ----------------------------------------
;                Initialize TCM
; ----------------------------------------
; TCM0(D-TCM, I-TCM) Configuration
                mov     r0,#0x0
                mcr        p15,0,r0,c9,c2,0        ; Write TCM Selection register

                ldr     r0,=ITCM0_BaseAddress
                mcr        p15,0,r0,c9,c1,1        ; Write Instruction TCM0 region register
                                
                ldr     r0,=DTCM0_BaseAddress
                mcr        p15,0,r0,c9,c1,0        ; Write Data TCM0 region register

; TCM1(D-TCM, I-TCM) Configuration
                mov     r0,#0x1
                mcr        p15,0,r0,c9,c2,0        ; Write TCM Selection register

                ldr     r0,=ITCM1_BaseAddress
                mcr        p15,0,r0,c9,c1,1        ; Write Instruction TCM1 region register
                                
                ldr     r0,=DTCM1_BaseAddress
                mcr        p15,0,r0,c9,c1,0        ; Write Data TCM0 region register
    ]
                
                IMPORT ScatterLoad
                LDR    R0, =ScatterLoad
                MOV    LR, PC
                BX    R0
                
                EXPORT    __main
__main
                ;; initialise the C library (which calls main())
                IMPORT    __rt_entry
                LDR    R0, =__rt_entry
                BX       R0
                
                   b        .
;=======================================================                  
                END
这个又有点复杂，哪位大哥能指点下迷津，帮我解答一下疑惑。谢谢啦！

呵呵，其实所谓的启动代码，其实是一段初始化代码，主要是初始化ARM的一些寄存器，初始化一下DRAM（能让后面的程序在DRAM里面运行），然后初始化一下堆栈（能运行C程序）。完成了上面的任务就行，复杂不复杂，完全可以看自己