cstartup_flash.arm

ARM入门的好帮手.包含了从简单到相对较复杂的程序.

;------------------------------------------------------------------------------
;-         ATMEL Microcontroller Software Support  -  ROUSSET  -
;------------------------------------------------------------------------------
; The software is delivered "AS IS" without warranty or condition of any
; kind, either express, implied or statutory. This includes without
; limitation any warranty or condition with respect to merchantability or
; fitness for any particular purpose, or against the infringements of
; intellectual property rights of others.
;-----------------------------------------------------------------------------
;- File source          : cstartup_flash.arm
;- Object               : Boot for Final Application version to be programmed 
;-                      : in flash or ROMed.
;- Compilation flag     : None
;-
;- 1.0 05/11/00 EL      : Creation Green Hills
;------------------------------------------------------------------------------

;------------------------------------------------------------------------------
;- Area Definition
;-----------------
;- Must be defined as function to put first in the code as it must be mapped
;- at offset 0 of the flash EBI_CSR0, ie. at address 0 before remap.
;------------------------------------------------------------------------------
                AREA        reset, CODE, READONLY, INTERWORK

;------------------------------------------------------------------------------
;- Remove any semihosting support
;--------------------------------
;- The C runtime library is the IO functions provided by the semihosting.
;- They are generally costly in code and unused as the debugger is not 
;- connected to the target. 
;- Must be removed if using the embedded C library is used.
;------------------------------------------------------------------------------
;- Define "__main" to ensure that C runtime system is not linked
                EXPORT      __main
__main

;------------------------------------------------------------------------------
;- Define the entry point
;------------------------
;- Note on the link address and the Remap command.
;- In order to guarantee that the non position-independant code (the ARM linker 
;- armlink doesn't generate position-independant code) can work on the ARM, 
;- it must be linked at address at which it expects to run. 
;- So the -ro-base must be used to define the link address as the base 
;- address of the flash.
;- In this startup example, we use 0x100 0000 as base address. That's flash 
;- address for all AT91 Evaluation Boards.
;------------------------------------------------------------------------------
                ENTRY

;------------------------------------------------------------------------------
;- Exception vectors ( before Remap )
;------------------------------------
;- These vectors are read at address 0 before remap.
;- They absolutely requires to be in relative addresssing mode in order to 
;- guarantee a valid jump. For the moment, all are just looping (what may be 
;- dangerous in a final system). If an exception occurs before remap, this 
;- would result in an infinite loop. 
;- After Remap, these vectors are mapped at address 0x100 0000 and only a 
;- reset (internal or external) can make of them the actual ARM vectors.
;- Note that the infinite loop has advantage that a debugger can to show up 
;- very quickly an hardware issue during the boot sequence.
;------------------------------------------------------------------------------
                B           InitReset       ; reset
undefvec
                B           undefvec        ; Undefined Instruction
swivec
                B           swivec          ; Software Interrupt
pabtvec
                B           pabtvec         ; Prefetch Abort
dabtvec 
                B           dabtvec         ; Data Abort
rsvdvec
                B           rsvdvec         ; reserved
irqvec
                B           irqvec          ; reserved
fiqvec
                B           fiqvec          ; reserved

;------------------------------------------------------------------------------
;- Exception vectors ( after Remap )
;------------------------------------
;- These vectors are read at address 0 after the remap command is performed in
;- the EBI. As they will be relocated at address 0x0 to be effective, a 
;- relative addressing is forbidden. The only possibility to get an absolute 
;- addressing for an ARM vector is to read a PC relative value at a defined
;- offset. It is easy to reserve the locations 0x20 to 0x3C (the 8 next
;- vectors) for storing the absolute exception handler address. 
;- The AIC vectoring access vectors are saved in the interrupt and fast 
;- interrupt ARM vectors. So, only 5 offsets are required ( reserved vector
;- offset is never used).
;- The provisory handler addresses are defined on infinite loop and can be 
;- modified at any time.
;- Note also that the reset is only accessible by a jump from the application 
;- to 0. It is an actual software reset.
;- As the 13 first location are used by the vectors, the read/write link 
;- address must be defined from 0x34 if internal data mapping is required.
;- (use for that the option -rw- base=0x34
;------------------------------------------------------------------------------
VectorTable
                ldr         pc, [pc, #0x18]          ; SoftReset
                ldr         pc, [pc, #0x18]          ; UndefHandler
                ldr         pc, [pc, #0x18]          ; SWIHandler
                ldr         pc, [pc, #0x18]          ; PrefetchAbortHandler
                ldr         pc, [pc, #0x18]          ; DataAbortHandler
                nop                                 ; Reserved
                ldr         pc, [pc,#-0xF20]        ; IRQ : read the AIC
                ldr         pc, [pc,#-0xF20]        ; FIQ : read the AIC

;- There are only 5 offsets as the vectoring is used.
                DCD         SoftReset
                DCD         UndefHandler
                DCD         SWIHandler
                DCD         PrefetchAbortHandler
                DCD         DataAbortHandler
;- Vectoring Execution function run at absolut addresss
SoftReset
                b           SoftReset
UndefHandler    
                b           UndefHandler
SWIHandler
                b           SWIHandler
PrefetchAbortHandler
                b           PrefetchAbortHandler
DataAbortHandler
                b           DataAbortHandler

;------------------------------------------------------------------------------
;- EBI Initialization Data
;-------------------------
;- The EBI values depend to target choice , Clock, and memories access time.
;- Yous must be define these values in include file
;- The EBI User Interface Image which is copied by the boot.
;- The EBI_CSR_x are defined in the target and hardware depend.
;- That's hardware! Details in the Electrical Datasheet of the AT91 device.
;- EBI Base Address is added at the end for commodity in copy code.
;------------------------------------------------------------------------------
InitTableEBI
            DCD         EBI_CSR_0  
            DCD         EBI_CSR_1  
            DCD         EBI_CSR_2  
            DCD         EBI_CSR_3  
            DCD         EBI_CSR_4  
            DCD         EBI_CSR_5  
            DCD         EBI_CSR_6  
            DCD         EBI_CSR_7  
            DCD         0x00000001  ; REMAP command
            DCD         0x00000006  ; 6 memory regions, standard read
PtEBIBase
            DCD         EBI_BASE    ; EBI Base Address

;------------------------------------------------------------------------------
;- The reset handler before Remap
;--------------------------------
;- From here, the code is executed from address 0. Take care, as it is linked 
;- in 0x100 0000.
;------------------------------------------------------------------------------
InitReset

;------------------------------------------------------------------------------
;- Speed up the Boot sequence
;----------------------------
;- After reset, the number os wait states on chip select 0 is 8. All AT91 
;- Evaluation Boards fits fast flash memories, so that the number of wait 
;- states can be optimized to fast up the boot sequence.
;------------------------------------------------------------------------------
;- Load System EBI Base address and CSR0 Init Value
                ldr     r0, PtEBIBase
                ldr     r1, [pc,#-(8+.-InitTableEBI)] ; values (relative)
    
;- Speed up code execution by disabling wait state on Chip Select 0
                str     r1, [r0]

;------------------------------------------------------------------------------
;- low level init
;--------------------------------
; Call __low_level_init to perform initialization before initializing
; AIC and calling main. 
;----------------------------------------------------------------------

                bl      __low_level_init

;------------------------------------------------------------------------------
;- Reset the Interrupt Controller
;--------------------------------
;- Normally, the code is executed only if a reset has been actually performed.
;- So, the AIC initialization resumes at setting up the default vectors.
;------------------------------------------------------------------------------
;- Load the AIC Base Address and the default handler addresses
                add     r0, pc,AicData-8-.  ; @ where to read values (relative)

                ldmia   r0, {r1-r4}

;- Setup the Spurious Vector
                str     r4, [r1, #AIC_SPU]      ; r4 = spurious handler

;- Set up the default interrupt handler vectors
                str     r2, [r1, #AIC_SVR]      ; SVR[0] for FIQ
                add     r1, r1, #AIC_SVR
                mov     r0, #31                 ; counter
LoopAic1
                str     r3, [r1, r0, LSL #2]    ; SVRs for IRQs
                subs    r0, r0, #1              ; do not save FIQ
                bhi     LoopAic1

                b       EndInitAic

;- Default Interrupt Handlers