s3c2410start.s.txt

bootloader 的启动汇编代码 start.s的注释

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

	GET option.inc      ;汇编文件的头文件，GET也可以用INCLUDE              
	GET memcfg.inc
	GET 2410addr.inc

BIT_SELFREFRESH EQU	(1<<22)

;Pre-defined constants
USERMODE    EQU 	0x10   ;PSR寄存器中的模式位，决定处理器操作模式，详见um_s3c2410a_manual_r10.pdf中page.75
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 ~  ;各种模式下的堆顶。_STACK_BASEADDRESS在option.inc中定义
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$$RO$$Base|   ; Base of ROM code
	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	

	
	AREA    SelfBoot, CODE, READONLY

	ENTRY
	
	EXPORT	__ENTRY
__ENTRY	
ResetEntry
	;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    ;程序从这里开始执行
    ]
	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
	ldr r0,[r1]
	mov pc,r0

	LTORG   
HandlerFIQ      HANDLER HandleFIQ
HandlerIRQ      HANDLER HandleIRQ
HandlerUndef    HANDLER HandleUndef
;HandlerUndef
;	sub	sp, sp, #4		;decrement sp(to store jump address)
;	stmfd	sp!, {r14}		;PUSH the work register to stack(lr does't push because it return to original address)
;	ldr	r0, =HandleUndef	;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}	
HandlerSWI      HANDLER HandleSWI
HandlerDabort   HANDLER HandleDabort
HandlerPabort   HANDLER HandlePabort

IsrIRQ  
	sub	sp, sp, #4       ;reserved for PC
	stmfd	sp!, {r8-r9}
	
	ldr	r9, =INTOFFSET
	ldr	r9, [r9]
	ldr	r8, =HandleEINT0
	add	r8, r8,r9,lsl #2
	ldr	r8, [r8]
	str	r8, [sp,#8]
	ldmfd	sp!,{r8-r9,pc}

;=======
; ENTRY  
;=======
ResetHandler
	ldr	r0,=WTCON       ;watch dog disable 
	ldr	r1,=0x0         
	str	r1,[r0]

	ldr	r0,=INTMSK
	ldr	r1,=0xffffffff  ;all interrupt disable
	str	r1,[r0]

	ldr	r0,=INTSUBMSK
	ldr	r1,=0x3ff		;all sub interrupt disable
	str	r1,[r0]

	[ {FALSE}
	; rGPFDAT = (rGPFDAT & ~(0xf<<4)) | ((~data & 0xf)<<4);    
	; Led_Display
	ldr	r0,=GPFCON
	ldr	r1,=0x5500		
	str	r1,[r0]
	ldr	r0,=GPFDAT
	ldr	r1,=0x10
	str	r1,[r0]
	]
	
	;To reduce PLL lock time, adjust the LOCKTIME register. 
	ldr	r0,=LOCKTIME
	ldr	r1,=0xffffff
	str	r1,[r0]
        
    [ PLL_ON_START
	;Configure MPLL
	ldr	r0,=MPLLCON
	ldr	r1,=((M_MDIV<<12)+(M_PDIV<<4)+M_SDIV)  ;Fin=12MHz,Fout=50MHz
	str	r1,[r0]
	]

	;Check if the boot is caused by the wake-up from POWER_OFF mode.
;	ldr	r1,=GSTATUS2
;	ldr	r0,[r1]
;	tst	r0,#0x2
	;In case of the wake-up from POWER_OFF mode, go to POWER_OFF_WAKEUP handler. 
;	bne	WAKEUP_POWER_OFF

	EXPORT StartPointAfterPowerOffWakeUp
StartPointAfterPowerOffWakeUp

	;Set memory control registers
	adr	r0, SMRDATA	;can't use ldr r0, =xxxx important!!!
	ldr	r1, =BWSCON	;BWSCON Address
	add	r2, r0, #52	;End address of SMRDATA  ;SMRDATA总共有13×4＝52 Bytes
0       
	ldr	r3, [r0], #4    ;把内存区中预先定义好的数据写往寄存器，从BWSCON～MRSR7
	str	r3, [r1], #4    
	cmp	r2, r0		
	bne	%B0

        ;Initialize stacks
	bl	InitStacks
	
  	; Setup IRQ handler
	ldr	r0,=HandleIRQ       ;This routine is needed
	ldr	r1,=IsrIRQ          ;if there isn't 'subs pc,lr,#4' at 0x18, 0x1c
	str	r1,[r0]

	ldr	r0, =BWSCON                                                 ;上面已经设置好BWSCON，在这里可以使用了
	ldr	r0, [r0]
	ands	r0, r0, #6		;OM[1:0] != 0, NOR FLash boot       ;查看BWSCON[2:1]，这两位就是OM[1:0]
	bne	copy_proc_beg		;don't read nand flash              ;if r0!=0 ，jump to copy_proc_beg。在这里，OM[2:1]肯定为0，即r0=0，所以跳过这句不执行，执行下一句
	adr	r0, ResetEntry		;OM[1:0] == 0, NAND FLash boot      ;(1)此时r0=0。按照我的理解，由于使用的是adr指令，该指令将基于PC相对偏移的地址值读取到寄存器中，编译器会使用一条合适的ADD或SUB指令来实现该指令的功能。对于adr r0, ResetEntry，编译器产生的替代指令为sub r0,pc,0x258，这个0x258就是ResetEntry到该语句的偏移值(注：0x258是通过反汇编看到的，大了两个字，但不影响分析)。此时由于这部分代码还在SRAM(低地址)中运行，pc值为0x250，所以相减得到r0=0;如果该句是在SDRAM(高地址)中运行，则pc值为0x30100250,所以相减得到r0=0x30100000。我们在AXD中用Armulator查看运行过程，其实它已经认为这些代码都已经在SDRAM中了。
	cmp	r0, #0			;if use Multi-ice,                  ;如果使用Multi-ice，则代码都下载到了0x30100000开始的SDRAM中了，所以ResetEntry=0x30100000,r0=0x30100000,跳转到copy_proc_beg。在使用Armulator时也是这种情况。但在上一句分析中得到了r0=0。 
	bne	copy_proc_beg		;don't read nand flash for boot     ; if r0!=0 jump to copy_proc_beg，但此时r0=0，不执行这一句，执行下一句nand_boot_beg
;===========================================================
nand_boot_beg
	mov	r5, #NFCONF
	ldr	r0,	=(1<<15)|(1<<12)|(1<<11)|(7<<8)|(7<<4)|(7)
	str	r0,	[r5]
	
	bl	ReadNandID
	mov	r6, #0             ;r6表示什么意思？
	ldr	r0, =0xec73
	cmp	r5, r0             ;r5为返回值 0xec76
	beq	%F1