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

[Russell, Don]

Hello,

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.


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???

IVPR=0 and IVOR6=0x700 appear to be set correctly.


Thanks
Don Russell


in service routine

MSR=0x9000, srr0=0x7088
ivpr=0x0, ivor6=0x700
pc= 0x403C , ad=0x1FF4E498
msr 0x00029000
lr  0x00004034
cr  0x24022222
trap 0x00000700


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