[ECOS] vector.s branch 0 problem

Alexandre thekyz@gmail.com
Mon Jul 2 13:34:00 GMT 2007


Hi everyone,

I may have a found why my ecos does not work at all but i'd like so
feedback on it.
I used the command:
arm-elf-objdump -h -S -C vectors.o > vectors.lss
to have a clearer view of what was going on at the init scale.
Everything seemed nice so far but this morning i noticed that on the
rom vectors init:

Disassembly of section .vectors:

00000000 <__exception_handlers>:
   0:	eafffffe 	b	0 <__exception_handlers>
   4:	e59ff018 	ldr	pc, [pc, #24]	; 24 <.undefined_instruction>
   8:	e59ff018 	ldr	pc, [pc, #24]	; 28 <.software_interrupt>
   c:	e59ff018 	ldr	pc, [pc, #24]	; 2c <.abort_prefetch>
  10:	e59ff018 	ldr	pc, [pc, #24]	; 30 <.abort_data>
  14:	b4405f62 	strltb	r5, [r0], -#3938
  18:	e59ff018 	ldr	pc, [pc, #24]	; 38 <.IRQ>
  1c:	e59ff018 	ldr	pc, [pc, #24]	; 3c <.FIQ>

I'm not a real genius when it come to assembly language but seems to
me the thing just loops forever at address 0.

I lurked a bit into vector.s and found the code that generated the
part above was that:

        .global __exception_handlers
__exception_handlers:
#ifdef CYGSEM_HAL_ROM_RESET_USES_JUMP
// Assumption:  ROM code has these vectors at the hardware reset address.
// A simple jump removes any address-space dependencies [i.e. safer]
        b       reset_vector                    // 0x00
#else
        ldr     pc,.reset_vector                // 0x00
#endif
        ldr     pc,.undefined_instruction       // 0x04
        ldr     pc,.software_interrupt          // 0x08 start && software int
        ldr     pc,.abort_prefetch              // 0x0C
        ldr     pc,.abort_data                  // 0x10
#ifdef CYGNUM_HAL_ARM_VECTOR_0x14
        .word   CYGNUM_HAL_ARM_VECTOR_0x14
#else
        .word   0                               // unused
#endif
        ldr     pc,.IRQ                         // 0x18
        ldr     pc,.FIQ                         // 0x1C

Now if we take a closer look at the code at 0, it is supposed to
branch to the start of the reset_vector. I noticed there's isn't a "."
(dot) at the start of the name, don't know if it's important or not
but as those are right from the cvs i thought it would be improper to
change it.

Do you guys have any idea what comes wrong here ?

Thanks in advance.

Alex

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