2020年01月02日 | ARM裸机篇---启动代码分析

先搞清楚启动代码和Bootloader的区别，启动代码是指CPU复位后到进入C语言的main函数之前需要执行的那段汇编代码。

下面的代码先暂且这样吧，没啥注释的，时间关系，我还是先搞些应用再说^_^

;=========================================

; NAME: 2410INIT.S

; DESC: C start up codes

;       Configure memory, ISR ,stacks

;   Initialize C-variables

; HISTORY:

; 2002.02.25:kwtark: ver 0.0

; 2002.03.20:purnnamu: Add some functions for testing STOP,POWER_OFF mode

; 2002.04.10:SJS:sub interrupt disable 0x3ff -> 0x7ff 

;=========================================

    GET option.s

    GET memcfg.s

    GET 2410addr.s 

BIT_SELFREFRESH EQU (1<<22)

;Pre-defined constants

USERMODE    EQU     0x10

FIQMODE     EQU     0x11

IRQMODE     EQU     0x12

SVCMODE     EQU     0x13

ABORTMODE   EQU     0x17

UNDEFMODE   EQU     0x1b

MODEMASK    EQU     0x1f

NOINT       EQU     0xc0

;The location of stacks

UserStack   EQU (_STACK_BASEADDRESS-0x3800) ;0x33ff4800 ~ 

SVCStack    EQU (_STACK_BASEADDRESS-0x2800) ;0x33ff5800 ~

UndefStack  EQU (_STACK_BASEADDRESS-0x2400) ;0x33ff5c00 ~

AbortStack  EQU (_STACK_BASEADDRESS-0x2000) ;0x33ff6000 ~

IRQStack    EQU (_STACK_BASEADDRESS-0x1000) ;0x33ff7000 ~

FIQStack    EQU (_STACK_BASEADDRESS-0x0)    ;0x33ff8000 ~ 

;Check if tasm.exe(armasm -16 ...@ADS 1.0) is used.

    GBLL    THUMBCODE

    [ {CONFIG} = 16 

THUMBCODE SETL  {TRUE}

        CODE32

        |   

THUMBCODE SETL  {FALSE}

        ]

        MACRO

    MOV_PC_LR

        [ THUMBCODE

            bx lr

        |

            mov pc,lr

        ]

    MEND

        MACRO

    MOVEQ_PC_LR

        [ THUMBCODE

            bxeq lr

        |

            moveq pc,lr

        ] 

    MEND

        MACRO

$HandlerLabel HANDLER $HandleLabel

$HandlerLabel

    sub sp,sp,#4        ;decrement sp(to store jump address)

    stmfd   sp!,{r0}        ;PUSH the work register to stack(lr does't push because it return to original address)

    ldr     r0,=$HandleLabel;load the address of HandleXXX to r0

    ldr     r0,[r0]         ;load the contents(service routine start address) of HandleXXX

    str     r0,[sp,#4]      ;store the contents(ISR) of HandleXXX to stack

    ldmfd   sp!,{r0,pc}     ;POP the work register and pc(jump to ISR)

    MEND

    IMPORT  |Image$$RO$$Limit|  ; End of ROM code (=start of ROM data)

    IMPORT  |Image$$RW$$Base|   ; Base of RAM to initialise

    IMPORT  |Image$$ZI$$Base|   ; Base and limit of area

    IMPORT  |Image$$ZI$$Limit|  ; to zero initialise

    IMPORT  Main    ; The main entry of mon program 

    AREA    Init,CODE,READONLY

    ENTRY  

    ;1)The code, which converts to Big-endian, should be in little endian code.

    ;2)The following little endian code will be compiled in Big-Endian mode. 

    ;  The code byte order should be changed as the memory bus width.

    ;3)The pseudo instruction,DCD can't be used here because the linker generates error.

    ASSERT  :DEF:ENDIAN_CHANGE

    [ ENDIAN_CHANGE

        ASSERT  :DEF:ENTRY_BUS_WIDTH

        [ ENTRY_BUS_WIDTH=32

        b   ChangeBigEndian     ;DCD 0xea000007 

        ]

        [ ENTRY_BUS_WIDTH=16

        andeq   r14,r7,r0,lsl #20   ;DCD 0x0007ea00

        ]

        [ ENTRY_BUS_WIDTH=8

        streq   r0,[r0,-r10,ror #1] ;DCD 0x070000ea

            ]

    |

        b   ResetHandler  

        ]

    b   HandlerUndef    ;handler for Undefined mode

    b   HandlerSWI  ;handler for SWI interrupt

    b   HandlerPabort   ;handler for PAbort

    b   HandlerDabort   ;handler for DAbort

    b   .       ;reserved

    b   HandlerIRQ  ;handler for IRQ interrupt 

    b   HandlerFIQ  ;handler for FIQ interrupt

;@0x20

    b   EnterPWDN

ChangeBigEndian

;@0x24

    [ ENTRY_BUS_WIDTH=32

        DCD 0xee110f10  ;0xee110f10 => mrc p15,0,r0,c1,c0,0

        DCD 0xe3800080  ;0xe3800080 => orr r0,r0,#0x80;  //Big-endian

        DCD 0xee010f10  ;0xee010f10 => mcr p15,0,r0,c1,c0,0

    ]

    [ ENTRY_BUS_WIDTH=16

        DCD 0x0f10ee11

        DCD 0x0080e380  

        DCD 0x0f10ee01  

    ]

    [ ENTRY_BUS_WIDTH=8

        DCD 0x100f11ee  

        DCD 0x800080e3  

        DCD 0x100f01ee  

        ]

    DCD 0xffffffff  ;swinv 0xffffff is similar with NOP and run well in both endian mode. 

    DCD 0xffffffff

    DCD 0xffffffff

    DCD 0xffffffff

    DCD 0xffffffff

    b ResetHandler

;Function for entering power down mode

; 1. SDRAM should be in self-refresh mode.

; 2. All interrupt should be maksked for SDRAM/DRAM self-refresh.

; 3. LCD controller should be disabled for SDRAM/DRAM self-refresh.

; 4. The I-cache may have to be turned on. 

; 5. The location of the following code may have not to be changed.

;void EnterPWDN(int CLKCON); 

EnterPWDN           

    mov r2,r0       ;r2=rCLKCON

    tst r0,#0x8     ;POWER_OFF mode?

    bne ENTER_POWER_OFF

ENTER_STOP  

    ldr r0,=REFRESH     

    ldr r3,[r0]     ;r3=rREFRESH    

    mov r1, r3

    orr r1, r1, #BIT_SELFREFRESH

    str r1, [r0]        ;Enable SDRAM self-refresh

    mov r1,#16      ;wait until self-refresh is issued. may not be needed.

0   subs r1,r1,#1

    bne %B0

    ldr r0,=CLKCON      ;enter STOP mode.

    str r2,[r0]    

    mov r1,#32

0   subs r1,r1,#1   ;1) wait until the STOP mode is in effect.

    bne %B0     ;2) Or wait here until the CPU&Peripherals will be turned-off

            ;   Entering POWER_OFF mode, only the reset by wake-up is available.

    ldr r0,=REFRESH ;exit from SDRAM self refresh mode.

    str r3,[r0]

    MOV_PC_LR

ENTER_POWER_OFF 

    ;NOTE.

    ;1) rGSTATUS3 should have the return address after wake-up from POWER_OFF mode.

    ldr r0,=REFRESH     

    ldr r1,[r0]     ;r1=rREFRESH    

    orr r1, r1, #BIT_SELFREFRESH

    str r1, [r0]        ;Enable SDRAM self-refresh

    mov r1,#16      ;Wait until self-refresh is issued,which may not be needed.

0   subs r1,r1,#1

    bne %B0

    ldr     r1,=MISCCR

    ldr r0,[r1]

    orr r0,r0,#(7<<17)  ;Make sure that SCLK0:SCLK->0, SCLK1:SCLK->0, SCKE=L during boot-up 

    str r0,[r1]

    ldr r0,=CLKCON

    str r2,[r0]    

    b .         ;CPU will die here.

WAKEUP_POWER_OFF

    ;Release SCLKn after wake-up from the POWER_OFF mode.

    ldr     r1,=MISCCR

    ldr r0,[r1]

    bic r0,r0,#(7<<17)  ;SCLK0:0->SCLK, SCLK1:0->SCLK, SCKE:L->H

    str r0,[r1]

    ;Set memory control registers

        ldr r0,=SMRDATA

    ldr r1,=BWSCON  ;BWSCON Address

    add r2, r0, #52 ;End address of SMRDATA

0       

    ldr r3, [r0], #4    

    str r3, [r1], #4    

    cmp r2, r0      

    bne %B0

    mov r1,#256

0   subs r1,r1,#1   ;1) wait until the SelfRefresh is released.

    bne %B0 

    ldr r1,=GSTATUS3    ;GSTATUS3 has the start address just after POWER_OFF wake-up