cstartup_flash.s

ARM入门的好帮手.包含了从简单到相对较复杂的程序.

                subs    r0, r0, #1              ; do not save FIQ
                bhi     LoopAic1

                b       EndInitAic

;- Default Interrupt Handlers
AicData
                DCD     AIC_BASE                ; AIC Base Address

;------------------------------------------------------------------------------
;- Default Interrupt Handler
;------------------------------------------------------
;- These function are defined in the AT91 library. If you want to change this 
;- you can redifine these function in your appication code
;------------------------------------------------------------------------------
                IMPORT  at91_default_fiq_handler
                IMPORT  at91_default_irq_handler
                IMPORT  at91_spurious_handler
PtDefaultHandler
                DCD     at91_default_fiq_handler
                DCD     at91_default_irq_handler
                DCD     at91_spurious_handler
EndInitAic

;------------------------------------------------------------------------------
;- Setup Exception Vectors in Internal RAM before Remap
;------------------------------------------------------
;- That's important to perform this operation before Remap in order to guarantee
;- that the core has valid vectors at any time during the remap operation.
;- Note: There are only 5 offsets as the vectoring is used.
;------------------------------------------------------------------------------
;- Copy the ARM exception vectors

                mov     r8, #RAM_BASE_BOOT          ; @ of the hard vector in internal RAM 0x300000
                add     r9, pc,#-(8+.-VectorTable)  ; @ where to read values (relative)
                ldmia   r9!, {r0-r7}            ; read 8 vectors
                stmia   r8!, {r0-r7}            ; store them
                ldmia   r9!, {r0-r4}            ; read 5 absolute handler addresses 
                stmia   r8!, {r0-r4}            ; store them

;------------------------------------------------------------------------------
;- Initialise the Memory Controller
;----------------------------------
;- That's principaly the Remap Command. Actually, all the External Bus 
;- Interface is configured with some instructions and the User Interface Image 
;- as described above. The jump "mov pc, r12" could be unread as it is after
;- located after the Remap but actually it is thanks to the Arm core pipeline.
;- The IniTableEBI addressing must be relative .
;- The PtInitRemap must be absolute as the processor jumps at this address 
;- immediatly after the Remap is performed.
;- Note also that the EBI base address is loaded in r11 by the "ldmia".
;------------------------------------------------------------------------------
;- Copy the Image of the Memory Controller
                sub     r10, pc,#(8+.-InitTableEBI) ; get the address of the chip select register image
                ldr     r12, PtInitRemap        ; get the real jump address ( after remap )

;- Copy Chip Select Register Image to Memory Controller and command remap
                ldmia   r10!, {r0-r9,r11}       ; load the complete image and the EBI base
                stmia   r11!, {r0-r9}           ; store the complete image with the remap command

;- Jump to ROM at its new address
                mov     pc, r12                 ; jump and break the pipeline

PtInitRemap
                DCD     InitRemap               ; address where to jump after REMAP 

;------------------------------------------------------------------------------
;- The Reset Handler after Remap
;-------------------------------
;- From here, the code is executed from its link address, ie. 0x100 0000.
;------------------------------------------------------------------------------
;InitRemap

;------------------------------------------------------------------------------
;- Stack Sizes Definition
;------------------------
;- Interrupt Stack requires 3 words x 8 priority level x 4 bytes when using
;- the vectoring. This assume that the IRQ_ENTRY/IRQ_EXIT macro are used. 
;- The Interrupt Stack must be adjusted depending on the interrupt handlers.
;- Fast Interrupt is the same than Interrupt without priority level.
;- Other stacks are defined by default to save one word each.
;- The System stack size is not defined and is limited by the free internal 
;- SRAM. 
;- User stack size is not defined and is limited by the free external SRAM.
;------------------------------------------------------------------------------

IRQ_STACK_SIZE      EQU     (3*8*4)     ; 3 words per interrupt priority level
FIQ_STACK_SIZE      EQU     (3*4)       ; 3 words
ABT_STACK_SIZE      EQU     (1*4)       ; 1 word
UND_STACK_SIZE      EQU     (1*4)       ; 1 word

;------------------------------------------------------------------------------
;- Top of Stack Definition
;-------------------------
;- Fast Interrupt, Interrupt, Abort, Undefined and Supervisor Stack are located
;- at the top of internal memory in order to speed the exception handling 
;- context saving and restoring.
;- User (Application, C) Stack is located at the top of the external memory.
;------------------------------------------------------------------------------

TOP_EXCEPTION_STACK     EQU     RAM_LIMIT           ; Defined in part
TOP_APPLICATION_STACK   EQU     EXT_SRAM_LIMIT      ; Defined in Target

;------------------------------------------------------------------------------
;- Setup the stack for each mode
;-------------------------------
                ldr     r0, =TOP_EXCEPTION_STACK

;- Set up Fast Interrupt Mode and set FIQ Mode Stack
                msr     CPSR_c, #ARM_MODE_FIQ:OR:I_BIT:OR:F_BIT
                mov     r13, r0                     ; Init stack FIQ
                sub     r0, r0, #FIQ_STACK_SIZE

;- Set up Interrupt Mode and set IRQ Mode Stack
                msr     CPSR_c, #ARM_MODE_IRQ:OR:I_BIT:OR:F_BIT
                mov     r13, r0                     ; Init stack IRQ
                sub     r0, r0, #IRQ_STACK_SIZE

InitRemap

;- Set up Abort Mode and set Abort Mode Stack
                msr     CPSR_c, #ARM_MODE_ABORT:OR:I_BIT:OR:F_BIT
                mov     r13, r0                     ; Init stack Abort
                sub     r0, r0, #ABT_STACK_SIZE

;- Set up Undefined Instruction Mode and set Undef Mode Stack
                msr     CPSR_c, #ARM_MODE_UNDEF:OR:I_BIT:OR:F_BIT
                mov     r13, r0                     ; Init stack Undef
                sub     r0, r0, #UND_STACK_SIZE

;- Set up Supervisor Mode and set Supervisor Mode Stack
                msr     CPSR_c, #ARM_MODE_SVC:OR:I_BIT:OR:F_BIT
                mov     r13, r0                     ; Init stack Sup

;------------------------------------------------------------------------------
;- Setup Application Operating Mode and Enable the interrupts
;------------------------------------------------------------
;- System Mode is selected first and the stack is setup. This allows to prevent 
;- any interrupt occurence while the User is not initialized. System Mode is
;- used as the interrupt enabling would be avoided from User Mode (CPSR cannot
;- be written while the core is in User Mode).
;------------------------------------------------------------------------------
                msr     CPSR_c, #ARM_MODE_USER      ; set User mode
                ldr     r13, =TOP_APPLICATION_STACK ; Init stack User
                
;------------------------------------------------------------------------------
;- Initialise C variables
;------------------------
;- Following labels are automatically generated by the linker. 
;- RO: Read-only = the code
;- RW: Read Write = the data pre-initialized and zero-initialized.
;- ZI: Zero-Initialized.
;- Pre-initialization values are located after the code area in the image.
;- Zero-initialized datas are mapped after the pre-initialized.
;- Note on the Data position : 
;- If using the ARMSDT, when no -rw-base option is used for the linker, the 
;- data area is mapped after the code. You can map the data either in internal
;- SRAM ( -rw-base=0x40 or 0x34) or in external SRAM ( -rw-base=0x2000000 ).
;- Note also that to improve the code density, the pre_initialized data must 
;- be limited to a minimum.
;------------------------------------------------------------------------------
                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

                ldr         r0, =|Image$$RO$$Limit| ; Get pointer to ROM data
                ldr         r1, =|Image$$RW$$Base|  ; and RAM copy
                ldr         r3, =|Image$$ZI$$Base|  ; Zero init base => top of initialised data
                cmp         r0, r1                  ; Check that they are different
                beq         NoRW
LoopRw          cmp         r1, r3                  ; Copy init data
                ldrcc       r2, [r0], #4
                strcc       r2, [r1], #4
                bcc         LoopRw
NoRW            ldr         r1, =|Image$$ZI$$Limit| ; Top of zero init segment
                mov         r2, #0
LoopZI          cmp         r3, r1                  ; Zero init
                strcc       r2, [r3], #4
                bcc         LoopZI

;------------------------------------------------------------------------------
;- Branch on C code Main function (with interworking)
;----------------------------------------------------
;- Branch must be performed by an interworking call as either an ARM or Thumb 
;- main C function must be supported. This makes the code not position-
;- independant. A Branch with link would generate errors 
;------------------------------------------------------------------------------
                IMPORT      main

                ldr         r0, =main
                mov         lr, pc
                bx          r0

;------------------------------------------------------------------------------
;- Loop for ever
;---------------
;- End of application. Normally, never occur.
;- Could jump on Software Reset ( B 0x0 ).
;------------------------------------------------------------------------------
End
                b           End
                
            END