[U-Boot-Users] u-boot ISR question

[Stefan Roese <sr@denx.de>]

Hi Don,

On Wednesday 15 February 2006 16:28, Russell, Don wrote:
> On  a ppc_440gx platform I wrote a small u-boot stand alone app for
> debugging. I tried to hook the ISR at 0x700 and use a trap instruction.

Hmmm. Do you want to connect an ISR like for external interrupts? That would 
be at 0x500 for 4xx platforms.

> I replaced the isr routine w/my own.   In the process I discovered the
> isr at 0x700 does nothing except store the address of the service
> routine and return handler at addresses 0x788 and 0x78c.
>
> I stubbed the entire routine and it still works as long as the
> above addresses are there.
>
> How does u-boot execute a trap instruction without executing at
> least a branch instruction from the trap location 0x700?
>
> How does it get to the global transfer_to_handler routine???

Could be that the 44x implementation is broken. If so a patch to fix this is 
most welcome. ;-)

<snip>

> addr=0x700,   0x4C00012C  =>isync istruction
> addr=0x704,   0x4C00012C
> addr=0x708,   0x4C00012C
> addr=0x70C,   0x4C00012C
> addr=0x710,   0x4C00012C
> addr=0x714,   0x4C00012C
> addr=0x718,   0x4C00012C
> addr=0x71C,   0x4C00012C
> addr=0x720,   0x4C00012C
> addr=0x724,   0x4C00012C
> addr=0x728,   0x4C00012C
> addr=0x72C,   0x4C00012C
> addr=0x730,   0x4C00012C
> addr=0x734,   0x4C00012C
> addr=0x738,   0x4C00012C
> addr=0x73C,   0x4C00012C
> addr=0x740,   0x4C00012C
> addr=0x744,   0x4C00012C
> addr=0x748,   0x4C00012C
> addr=0x74C,   0x4C00012C
> addr=0x750,   0x4C00012C
> addr=0x754,   0x4C00012C
> addr=0x758,   0x4C00012C
> addr=0x75C,   0x4C00012C
> addr=0x760,   0x4C00012C
> addr=0x764,   0x4C00012C
> addr=0x768,   0x4C00012C
> addr=0x76C,   0x4C00012C
> addr=0x770,   0x4C00012C
> addr=0x774,   0x4C00012C
> addr=0x778,   0x4C00012C
> addr=0x77C,   0x4C00012C
> addr=0x780,   0x4C00012C
> addr=0x784,   0x4C00012C
> addr=0x788,   0x6B1C               => trapservice location
> addr=0x78C,   0x7E60               => return handler location

Here a log from our Ocotea:

=> md 700
00000700: 7e9043a6 7eb143a6 7e800026 3aa1ff00    ~.C.~.C.~..&:...
00000710: 929500a8 92d50068 92f5006c 7e9042a6    .......h...l~.B.
00000720: 92950060 7ed142a6 92d50064 7e8802a6    ...`~.B....d~...
00000730: 929500a0 7ec902a6 92d5009c 7e8102a6    ....~.......~...
00000740: 929500a4 7eda02a6 7efb02a6 90150010    ....~...~.......
00000750: 90350014 90550018 90350000 7ea1ab78    .5...U...5..~..x
00000760: 9075001c 90950020 90b50024 90d50028    .u..... ...$...(
00000770: 38610010 3a801000 52f40420 80ce8014    8a..:...R.. ....
00000780: 7cc803a6 4e800021 0ffc7a10 0ffc719c    |...N..!..z...q.
00000790: 00000000 00000000 00000000 00000000    ................

This does not match your description. What version are you using?

Best regards,
Stefan