Asm programming

Why not study, experiment and learn to understand what's happening with the startup code. Leave the 'main' in C to begin with and remove it when you understand how to.

Why not study, experiment and learn to understand what's happening with the startup code. Leave the 'main' in C to begin with and remove it when you understand how to.

I compiled above program from command line and it is working. In Keil i can't compile it. It still needs Reset_Handler label even if I changed Start to Reset_Handler.

1 - Find an example program from Keil for your processor.
2 - Change the 'main' function to a do nothing.
3 - Compile the project.
4 - Now examine, understand and learn from the startup.

Simple.

There is no pure assembler project in Keil MDK.

Another problem. I don't know why the board executes only specified number of instructions. Here is the example:

STACK_TOP   EQU   0x10000200         ; constant for SP starting value
                        AREA  |Header Code|, CODE
            DCD    STACK_TOP  ; Stack top
            DCD    Start      ; Reset vector
            ENTRY             ; Indicate program execution start here
Start       ; Start of main program

                        MOV             R1, #10

                        MOVW    R3, #0xC040             ;P2.2, P2.3, P2.4, P2.5, and P2.6 function mode is located at FP2DIR (0×2009_C040).
                        MOVT    R3, #0x2009

                        MOVW    R2, #0x007C             ;P2.2  -> Bit[2] * P2.3  -> Bit[3]* P2.4  -> Bit[4]* P2.5  -> Bit[5]* P2.6  -> Bit[6] -> Output dir : 1
                        STR     R2, [R3]

loop

                        B       loop

END

This program executes correctly. It defines the GPIO ports as output. On board leds are off (after reset state normally all leds are on).
Then I modified the program by adding the same line

STACK_TOP   EQU   0x10000200         ; constant for SP starting value
                        AREA  |Header Code|, CODE
            DCD    STACK_TOP  ; Stack top
            DCD    Start      ; Reset vector
            ENTRY             ; Indicate program execution start here
Start       ; Start of main program

                        MOV             R1, #10
                     MOV             R1, #10

                        MOVW    R3, #0xC040             ;P2.2, P2.3, P2.4, P2.5, and P2.6 function mode is located at FP2DIR (0×2009_C040).
                        MOVT    R3, #0x2009

                        MOVW    R2, #0x007C             ;P2.2  -> Bit[2] * P2.3  -> Bit[3]* P2.4  -> Bit[4]* P2.5  -> Bit[5]* P2.6  -> Bit[6] -> Output dir : 1
                        STR     R2, [R3]

loop

                        B       loop

END

So normally the program does the same but now leds are still on so the instruction STR R2, [R3] is not executing.
Where is the problem?
I'm using keil compilers as follows:

"C:\Program Files\keil\ARM\BIN40\armasm" --device darmp1 -o .\blinky.o .\blinky.s
"C:\Program Files\keil\ARM\BIN40\armlink" --device darmp1 --rw_base 0x10000000 --ro_base 0x0 --map -o .\blinky.elf .\blinky.o
"C:\Program Files\keil\ARM\BIN40\fromelf" --bin --output .\blinky.bin .\blinky.elf
"C:\Program Files\keil\ARM\BIN40\fromelf" --i32 --output .\blinky.hex .\blinky.elf

"There is no pure assembler project in Keil MDK."

Who suggested there was?

The startup code is in assembler - So there would be the starting point.

Time to add a data-abort handler and reading about data alignments - R3 contains an unaligned address so

STR R2,[R3]

must generate an access fault...

must generate an access fault...

this is not true for all ARM processors. in fact, STR is documented to have the ability to handle unaligned accesses on ARM7 and Cortex M3 !

STR R2, [R3, #0] doesn't work also. Fro me the problem is not the instruction but one additional line in the code.
I copied the code from:
embeddedfreak.wordpress.com/.../
It is the same board.

Finally I wrote a program which can be compiled in Keil:

; <h> Stack Configuration
;   <o> Stack Size (in Bytes) <0x0-0xFFFFFFFF:8>
; </h>

Stack_Size      EQU     0x00000200

                AREA    STACK, NOINIT, READWRITE, ALIGN=3
Stack_Mem       SPACE   Stack_Size
__initial_sp


; <h> Heap Configuration
;   <o>  Heap Size (in Bytes) <0x0-0xFFFFFFFF:8>
; </h>

Heap_Size       EQU     0x00000000

                AREA    HEAP, NOINIT, READWRITE, ALIGN=3
__heap_base
Heap_Mem        SPACE   Heap_Size
__heap_limit

                PRESERVE8
                THUMB

; Vector Table Mapped to Address 0 at Reset

                AREA    RESET, DATA, READONLY
                EXPORT  __Vectors

__Vectors       DCD     __initial_sp              ; Top of Stack
                DCD     Reset_Handler             ; Reset Handler



                AREA    Program, CODE, READONLY

                                EXPORT Reset_Handler            ;Defines the program starting point

;Program start

Reset_Handler

                        MOV             R1, #0

                        MOVW    R3, #0xC040             ;P2.2, P2.3, P2.4, P2.5, and P2.6 function mode is located at FP2DIR (0×2009_C040).
                        MOVT    R3, #0x2009

                        MOVW    R2, #0x007C             ;P2.2  -> Bit[2] * P2.3  -> Bit[3]* P2.4  -> Bit[4]* P2.5  -> Bit[5]* P2.6  -> Bit[6] -> Output dir : 1
                        MOVT    R2, #0x0000             ;/* b0000_0000_0000_0000_0000_0000_0111_1100 */
                        STR     R2, [R3, #0]


loop

                        B       loop

                        END

The first part was copied from build-in startup file.
But it didn't fix the problem....

Gp F wrote:
> R3 contains an unaligned address

Really? The value in r3 is 0x2009C040. Looks aligned to me.

MOVW assigns the lower half-word and clears the upper. MOVT assigns
the upper half-word. Easier to use here would be the pseudo
instruction

MOV32 r3, #0x2009C040

Tamir wrote:
> in fact, STR is documented to have the ability to handle unaligned
> accesses on ARM7 and Cortex M3 !

Depends on what is meant by "handle". ARM7 has a rather creative way
of dealing with unaligned accesses -- the results would be unexpected
to most people who are unfamiliar with architecture details.

Cortex-M3 does handle unaligned accesses but not in all
situations. Check out the documentation.

--
Marcus
http://www.doulos.com/arm/

I found the sollution. Probabely the program code was in reserver region. I copied all startup code (all vector table) and now it is working properly. I found it in dissasembled code. In all built in projects the first instruction was in higher address than 0x18 in my code.
Now I use build in startup file but I have to comment one line:

 User Initial Stack & Heap

                IF      :DEF:__MICROLIB

                EXPORT  __initial_sp
                EXPORT  __heap_base
                EXPORT  __heap_limit

                ELSE

; IMPORT  __use_two_region_memory
                EXPORT  __user_initial_stackheap
__user_initial_stackheap

                LDR     R0, =  Heap_Mem
                LDR     R1, =(Stack_Mem + Stack_Size)
                LDR     R2, = (Heap_Mem +  Heap_Size)
                LDR     R3, = Stack_Mem
                BX      LR

                ALIGN

                ENDIF

because i get following messages:
blinky.axf: Warning: L6665W: Neither Lib$$Request$$armlib Lib$$Request$$cpplib defined, not searching ARM libraries.
blinky.axf: Error: L6218E: Undefined symbol __use_two_region_memory (referred from startup_lpc17xx.o).