[U-Boot-Users] unexpected behaviour !!!

[U-Boot-Users] unexpected behaviour !!!

[Maximus]

Hi,
    I have designed my own protocol and am trying to include it in u-boot.


    In the Recieve Handler i am trying to dereference the pkt.

struct mypacket {
    unsigned int seqnum ;
    char data [24] ;
} ;

struct mypacket mypacket ;

void myrecieve_handler (uchar * pkt, unsigned dest, unsigned src, unsigned len)
{
    int seqnum ;
    uchar * q ;

    if (dest != 8888)
        return ;

    printf ("pkt => %u\n", pkt) ;
    printf ("len => %d\n", len) ;


  q = pkt ;
  for (i = 0 ; i < len ; i++) {
      printf ("%d:%u=> %c\n", i, q, *q) ;
      q++ ;
  }

    memcpy (&mypacket, pkt, sizeof (mypacket)) ;
    printf ("seq:%u\n", mypacket.seq) ;
    printf ("data:%s\n", mypacket.data) ;
    printf ("before\n") ;
    seqnum = * (int *) pkt ;                /*
<------------------------   Abort - Board Hangs */
    printf ("after\n") ;

}

I am able to access the contents of pkt
   1) byte by byte
   2) memcpy

But, as soon as i try to deference it either by doing
     1) * (int *) pkt  /***************** board hangs ********/
            or
     2) mp = (struct mypacket *) pkt
           printf ("%u\n", mp -> seqnum) ;  /************* board Hangs
*************/

I get the Error shown below.

As, soon as seqnum = * (int *) pkt - is executed my board prints the message:


Why is that ?.


I dont understand this. i am using an OMAP 5912 OSK BOARD.


Is it not possible to dereference pkt ?.



data abort
pc : [<2000d6b0>]    lr : [<2000d6a8>]
sp : 1ffbfc38  ip : ffffffff  fp : 20015fc8
r10: 2001dc24  r9 : 20015fb8  r8 : 1ffbffdc
r7 : 2001dc08  r6 : 0000001c  r5 : 2001c40a  r4 : 000022b8
r3 : 00000020  r2 : 00000001  r1 : 0000000a  r0 : 00000000
Flags: nZCv  IRQs off  FIQs off  Mode SVC_32
Resetting CPU ...


Regards,
Jo

[U-Boot-Users] unexpected behaviour !!!

[Peter Menzebach]

Maximus wrote:
...
> void myrecieve_handler (uchar * pkt, unsigned dest, unsigned src, unsigned len)
> {
...
> 
> As, soon as seqnum = * (int *) pkt - is executed my board prints the message:
> 

One idea without further investigation....

if the pointer pkt is *not* on an 4 byte aligned address, you will get 
an alignment trap on arm.

Best regards
Peter

[U-Boot-Users] Re: unexpected behaviour !!!

[Maximus]

Hi,
    Thanks a lot - it took me 2 days to find it out!!!.

    The address of a long int, struct should be aligned to address
which a multiple of 4.



Regards,
Jo


On 1/31/06, Peter Menzebach <pm-ub@mw-itcon.de> wrote:
> Maximus wrote:
> ...
> > void myrecieve_handler (uchar * pkt, unsigned dest, unsigned src, unsigned
> len)
> > {
> ...
> >
> > As, soon as seqnum = * (int *) pkt - is executed my board prints the
> message:
> >
>
> One idea without further investigation....
>
> if the pointer pkt is *not* on an 4 byte aligned address, you will get
> an alignment trap on arm.
>
> Best regards
> Peter
>

[U-Boot-Users] Re: unexpected behaviour !!!

[Andreas Schweigstill]

Dear Maximus!

Maximus schrieb:
 > Thanks a lot - it took me 2 days to find it out!!!.

Have you ever read a book or taken a course about ARM
architecture? It doesn't seem like this, but it is
extremely important to understand the processor
architecture when working with it.

With best regards
Andreas Schweigstill


-- 
Dipl.-Phys. Andreas Schweigstill
Schweigstill IT | Embedded Systems
Schauenburgerstra?e 116, D-24118 Kiel, Germany
Phone: (+49) 431 5606-435, Fax: (+49) 431 5606-436
Mobile: (+49) 171 6921973, Web: http://www.schweigstill.de/