Hi,

On  a 440gx platform I wrote  a small 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?  IVPR and IVOR6 are set correctly.

How does it get to the global transfer_to_handler routine??

Thanks

Don Russell

+$#00-$DOK#demsg:#

in svc rtn

MSR=0x9000, srr0=0x7088

ivpr=0x0, ivor6=0x700

pc= 0x403C , ad=0x1FF4E498

msr 0x00029000

lr  0x00004034

cr  0x24022222

trap 0x00000700

addr=0x700,   0x4C00012C  =isync

 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

 addr=0x78C,   0x7E60               =return handler

 +$#00