Hi Experts,I have just started with ARM assembly, I have written a program in assembly for toggling GPIO. The issue that I am facing is that the code works when I use several "nop" in place of "bl delay". The code goes below:
.equ IODIR0, 0xE0028008 .equ IOCLR0, 0xE002800C .equ IOSET0, 0xE0028004 delay: mov r0, #10 dowaitloop: subs r0,#1 bne dowaitloop bx lr MOV r3, #0xFFFFFFFF LDR r4, =IODIR0 LDR r1, =IOCLR0 LDR r2, =IOSET0 str r3, [r4] loop: str r3, [r1] bl delay str r3, [r2] bl delay b loop
Commands that I execute to compile:arm-none-eabi-as -gcoff -o blinky.o blinky.sarm-none-eabi-ld -e0x00000000 -Ttext=0x00000000 -o blinky.elf blinky.o
arm-none-eabi-objcopy -Oihex blinky.elf blinky.hex
Hi,
the _start symbol would be useless because there is no means to initiate from the _start.
If you use assembler, you had better put the vector table from the address 0x0.
The program will begin with the address 0x0.
For exsample:
.global _start .equ IODIR0, 0xE0028008 .equ IOCLR0, 0xE002800C .equ IOSET0, 0xE0028004 .text b _start b undef_handler b SVC_handler b PAbt_handelr b DAbt_handler b RFU_handler b IRQ_handler b FIQ_handler undef_handler: SVC_handler: PAbt_handelr: DAbt_handler: RFU_handler: IRQ_handler: FIQ_handler: b undef_handler /* do nothing */ delay: mov r0, #10 dowaitloop: subs r0,#1 bne dowaitloop bx lr _start: MOV r3, #0xFFFFFFFF LDR r4, =IODIR0 LDR r1, =IOCLR0 LDR r2, =IOSET0 str r3, [r4] loop: str r3, [r2] bl delay str r3, [r1] bl delay b loop
Best regards,
Yasuhiko Koumoto.