Linux boot issues

[Jerry Van Baren]

At 01:17 PM 2/8/2002 -0600, Navin Boppuri wrote:

>Hello again,
>
>I have PPCBOOT 1.1.2 running on my hardware with an MPC855T processor
>running at 64MHZ (both core and bus). I have SDRAM interfaced on this
>hardware and I think the burst accesses are working fine since PPCBOOT is
>executing well with burst accesses turned on. I have a 2.4.2 Linux kernel
>programmed in flash and I am trying to boot this kernel on the hardware.
>
>I have a BDI hooked up to this hardware.
>
>The problem is when I start booting the kernel, PPCBOOT calculates the
>checksum and says it is OK. It then uncompresses the kernel and even that
>is successful. The processor then goes into the debug state and halts at
>instruction 0xc000fa0c with a Software Emulation exception. When I do a
>disassemble of the Linux kernel, I see that this instruction is the start
>of the "printk" routine. No matter how many times I do this, I break at
>exactly the same instruction.

This is almost invariably a very strong clue that you are trying to execute
0xFFxxxxxx as an instruction.  It usually happens because you jumped to the
wrong location or you have a memory fetch problem.  In your case, everybody
on the list is betting on option #2.

I don't have a PPC board handy for disassembling a 0xFFFFFFFF opcode, but
from the "PowerPC 603e RISC Microprocessor User's Manual" Appendix A, page
A-15 it looks like 0xFFFFFFFF is a fnmaddx instruction (floating point
multiply and add).

 From the MPC860 User's Manual:

7.1.2.11 Floating-Point Assist Exception
The foating-point assist exception is not generated by the MPC860.
Attempting to execute
a foating-point causes an instruction implementation-speciÞc software emulation
exception.



>I tried defining CONFIG_CLOCKS_IN_MHZ but that did not change anything. I
>also tried running the processor at 64Mhz/32Mhz (core/memory bus) and
>32Mhz/32Mhz but it did not make a difference.
>
>I was hoping that the kernel would come up atleast with burst accesses
>turned off, but I see the same exact behaviour even then.
>
>I am not sure what to look for now.
>
>Thank you for all the help and putting up with my weird queries.
>
>Navin Boppuri.
>
>


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